Unit 15 Immune System, Vaccination and Antibiotics
Key Unit Competence
To be able to describe the immune system and apply the knowledge gained in familiar andunfamiliar contexts.
LEARNING OBJECTIVES
At the end of this unit, the learner will be able to:
• State the origin and describe the mode of action of phagocytes.
• Describe the modes of action of B-lymphocytes and T-lymphocytes.
• Recognise phagocytes and lymphocytes under a light microscope.
• Explain the meaning of the term immune response, making reference to the terms antigen,
self and non-self.
• Support and promote national immunisation days.
• Explain the role of memory cells in long-term immunity.
• Explain the role of antibodies in allergies.
• Relate the molecular structure of antibodies to their functions.
• Interpret the differences between cellular responses and humoral responses.
• Distinguish between active and passive, natural and artificial immunity and explain how
vaccination can control disease.
• Distinguish between generalised and localised allergic reactions.
• Discuss causes, symptoms and treatment of asthma and hay fever.
• Support and have sympathy for asthmatic patients.
• Discuss the reasons why vaccination programmes have eradicated smallpox but not measles,
TB, malaria or cholera.
• Define antibiotic as a substance produced by one microorganism that is capable of destroying
or inhibiting the growth of another microorganism.
• Explain how antibiotics work.
• Explain the reasons for antibiotic resistance.
• Carry out research and be able to present findings on the reasons for antibiotic resistance inthe treatments of infections.
INTRODUCTORY ACTIVITY
The year 2020 will remain unforgettable because of the outbreak of the pandemic Covid-19.
WHO declared covid-19 pandemic disease. Wearing mask, using hydro alcoholic sanitizer to
wash hand and social distance were among the best preventive measures.
Aged people and chronicle disease patients were warned to take care.The picture below was taken during a youth meeting during the Covid-19 lockdown.
Youth meeting during Covid-19 lockdow
Who declared covid-19 pandemic disease?
Why Aged people and chronicle disease patients were warned to take care?Why Covid-19 is considered human threat?
Introduction
For a very long time, people held the view that something in the thin air or foul air arising
out of decomposing matter can cause illness. It was the pioneering work of scientists Louis
Pasteur and Robert Koch who laid the foundation of germ theory of disease, showing for
the first time that micro-organisms are responsible for causing various illnesses. Thus, in this
unit, we study how our body fights with these micro-organisms to keep us healthy; how our
immune systems are built; what is the role of vaccinations for building our immunity; and
how in the event of extreme illness one resorts to the use of antibiotics to control infections.
For example the year 2020 will remain unforgettable because of the outbreak of the pandemic
Covid-19.WHO declared covid-19 pandemic disease. Wearing mask, using hydro alcoholic
sanitizer to wash hand and social distance were among the best preventive measures.Aged
people and chronicle disease patients were warned to take care.
Who declared covid-19 pandemic disease?
Why aged people and chronicle disease patients were warned to take more care?Why Covid-19 is considered as human threat?
15.1 IMMUNE SYSTEM
ACTIVITY 1
Observe the prepared slides of blood smear under microscope, first under
10 X and then under
40 X magnification. Draw what all you observe and try to answer the following:
(i) Do you see cells? (ii) Are they all similar? (iii) What are the differences between different
types of cells? (iv) Which cells are most numerous? (v) What are they called? (vi) Which cellsare less numerous? (vii) Are these cells all alike? (viii) What does the stain indicate?
We are exposed to micro-organisms all the time, as they are present in large numbers in the air
we breathe, the food we eat and the water we drink. It is our defence system that keeps us free
of disease and constitutes our immune system. Immune system has two main components:Innate and Acquired.
15.1.1 Innate Immunity
Innate immunity is present at birth and depends
on:
(i) Anatomical and Physiological barriers,
(ii) White blood cells (mainly phagocytes)(iii) Some soluble mediators
Figure 15.1: Shows two neutrophils, one
monocyte and one lymphocyte among alarge number of RBCs
Anatomical and Physiological Barriers
Anatomical barriers consist of skin on the outside and mucous membranes lining gastrointestinal
tract, respiratory tract and genitourinary tract, while acidity in the stomach constitutes
Physiological barriers.
Skin is the largest organ of our body and presents a physical barrier for pathogens to prevent
their entry into the body. Some openings into the body are needed for the purpose of feeding,
breathing and reproduction. They are also the potential sites of entry of pathogens from
the environment. Therefore, the entire digestive tract, respiratory tract and genito-urinary
tract are lined by mucous membrane which does not allow pathogens to gain entry into the
tissues. High acidity within the stomach also helps to kill some pathogens ingested alongwith food.
White Blood Cells
White blood cells are the chief components giving us protection against infection.
When a blood smear is prepared, two types of cells can be identified: small, very numerous,
without nucleus called red blood cells (RBC) because they contain red pigment, haemoglobin
for oxygen transport and large, less numerous, with darkly staining nucleus called white blood
cells (WBC), because they do not contain red pigment. Among the WBCs, different cell types
can be distinguished:
(i) Phagocytes, which include neutrophils (having single, multi-lobed, nucleus) and monocytes
(having kidney-shaped nucleus) with a moderate amount of cytoplasm, and
(ii) Lymphocytes, with a very large, darkly staining nucleus occupying the entire volume of
the cell, with very little cytoplasm.
All blood cells arise within bone-marrow of long bones. RBCs and most WBCs complete their
development within the bone-marrow, while T-lymphocytes migrate to thymus for further
maturation and development. Monocytes circulate in blood for varying periods of time and
then migrate to tissues and differentiate into macrophages. As the most important function of
the immune system is to kill the pathogenic organisms to prevent the occurrence of disease, avery crucial attribute of immune system is to distinguish self from non-self.
In the absence of such a mechanism, the immune system might target one’s own tissues.
Identification of self from non-self is perfect by innate immune system, where-in receptors on
phagocytes recognize molecules present on microbial organisms as non-self. But lymphocytes,
which constitute adaptive immunity, may sometimes, target one’s own tissues, leading to the
generation of auto-immune diseases, e.g., rheumatoid arthritis, multiple sclerosis, systemiclupus erythematosus.
Mode of Action of Phagocytes
Phagocytes, which include both neutrophils and macrophages, play an important role in innate
immunity. They can identify foreign invading pathogens, discriminate them from cells of the
body, and internalize them by throwing pseudopodia around them. Once within the phagocytes,
pathogens are digested by a number of hydrolytic enzymes, thus freeing the body of disease-causinggerms. Phagocytes also help in removing old, dead cells as well as cancerous cells (Figure 15.2).
Figure 15.2: Showing process of phagocytosis by a macrophage
Soluble Mediators
Among soluble mediators of innate immunity are predominantly complement proteins which
can identify foreign microbial organisms and punch holes in their membranes, thus, effectively
killing them.
As soon as there is invasion of the body by any microbial organisms, innate branch of the
immune system immediately comes into operation as it is present from the time of birth.
However, if the infection persists, leading to the appearance of disease symptoms, it recruits
elements of second line of defence, the Specific or Adaptive immune system. Though both branches
of immune system help in eliminating the infectious agents, there are important differences in
the way these two systems work (see Table15.1).
Immune Response: Response produced by the body upon invasion of a foreign substance,
especially infectious microbes and toxins produced by them and is protective in nature.
Antigen: Any substance, that is foreign to the body, upon entering the body, evokes the generation
of immune response is called antigen. Infectious agents such as bacteria and viruses present alarge number of antigens to which the body responds by mounting an immune response.
15.1.2 Adaptive or Acquired Immune System
Adaptive or acquired immune system is not present at the time of birth but acquired during one’s
life-time. However, once acquired, its memory persists in the body in the form of memory cells
for a very long period of time. Generation of memory cells upon first exposure to infectious agent
is seen in primary response. Primary response leads to the generation of activated lymphocytes
of the B- or T- type as well as memory cells. This response is not only weak in intensity butalso takes a long time to initiate.
However, upon second exposure to the same infectious agent, the immune response generated is
faster and greater in intensity due to the already existing memory cells, and is called secondary
response (Table 15.2). It is the genesis of heightened immune response upon second exposure
that laid the foundation of all active vaccination programmes.Table 15.1: Comparing Innate and Adaptive Immunity
Table 15.2: Comparing primary and secondary immune response
Components of the Acquired or Adaptive Immunity
(i) Humoral Immunity: It is mediated by B-lymphocytes.(ii) Cell-mediated Immunity: It is achieved by T-lymphocytes.
Humoral Immunity: B lymphocytes
Humoral immunity was discovered by Emil Behring and Shibasaburo Kitasato in 1890.
This proved to be a landmark experiment and it earned von Behring Nobel Prize in Medicine.
This experiment showed two important things: one, that following infection or immunization,
substances appeared in serum that have the capacity to protect against the infective agent; this
laid the foundation of humoral branch of immunity; second, that immunity could be transferred
from immunized to non-immunized organism; this laid the foundation of strategy of passive
immunization. Generation of humoral response involves:
(a) Activation of B-lymphocytes
(b) Conversion of B-lymphocytes into plasma cells
(c) Secretion of antibodies(d) Functions performed by antibodies
B-lymphocytes, 6 micrometre in size, having a darkly staining, large nucleus, and very little
cytoplasm, bear receptors on their surface which recognize and bind antigens on microbial
organisms. Binding of receptors leads to activation of B-lymphocytes, which undergo a number
of mitotic divisions producing two kinds of cells, effecter cells called plasma cells and memory
cells. Memory cells are long lived, retain the same receptors as the original B-lymphocyte and
can get activated upon second exposure to the same infectious agent to give rise to a heightenedresponse (Figure 15.3).
Figure 15.3: Activation of B-lymphocyte
Effecter cells or plasma cells, about 15 micrometre in size, with a large amount of cytoplasm
having Golgi apparatus and endoplasmic reticulum, represent the end stage B-lymphocytes,
which do not further divide but actively secrete antibody molecules at a high rate.Antibodies are, proteins, called immunoglobulins, designated as Ig.
Fig15.4. Bonding between antibody and antigen
The diagram shows the basic structure of an antibody, which consists of four chains, two light and
two heavy joined by disulphide bonds, light chain and heavy chain at one end, together constitute
antigen binding site whereas constant region of two heavy chains performs the biological functions
as described below. Different classes of antibodies differ in the number of such monomers and the
numbers of disulphide bonds present in one molecule and hence are capable of performing different
functions. Example: IgM is a pentamer composed of five monomers
The five primary classes of immunoglobulins are IgG, IgM, IgA, IgD and IgE. These are
distinguished by the type of heavy chain found in the molecule. IgG molecules have heavy
chains known as gamma-chains; IgMs have mu-chains; IgAs have alpha-chains; IgEs have
epsilon-chains; and IgDs have delta-chains.. These antibodies are capable of recognising over
a million different antigens and confer protection in a number of ways. Functions performedby antibodies are:
1. Antibodies bind to toxins produced by bacteria that cause infection like diphtheria or
tetanus, effectively nullifying them.
2. By attaching to microbial pathogens, antibodies promote their clearance by phagocytes
manifold.
3. Antibodies form a covering on bacteria and viruses, not allowing them to gain entry into
tissues. Bacteria and viruses, thus having been coated, are eliminated by beating of cilia
present on the epithelial cells in the respiratory tract or by peristalsis of the gastrointestinal
tract.
Cell-Mediated Immune Response: T Lymphocyte
Though antibody molecules are highly specific and confer high degree of protection to the
body against toxins and microbes present in blood and extra-cellular fluids, they are not able
to neutralise those pathogens which live within the cells e.g., viruses, malarial parasite, some
bacteria such as Salmonella, Mycobaterium etc. Therefore, in order to protect the body from
intra-cellular infectious organisms as well as to eliminate cancerous cells, body mounts cellmediated
immune response.
Generation of cell-mediated immune response:
1. Recognition and binding of antigens by T-lymphocytes, macrophages, neutrophils, and
natural killer cells (NK). These cells differ in the way they bind antigens. T-lymphocytes
recognize and bind antigens only in association with another set of proteins called major
histocompatibility complex (MHC). Macrophages, neutrophils and NK cells can bind
to antibody-tagged cells.
2. T lymphocytes are of two types, helper T lymphocytes and Tc cells. Helper T lymphocytes
play important role in both humoral and cell mediated immunity by secreting important
cytokines.
3. Activation of the above mentioned cells (appearance of granules in T-lymphocytes and
macrophages which are normally agranulocytes). T-lymphocytes get transformed into
cytotoxic T lymphocytes, or CTL.
4. Secretion of cytotoxic chemicals/cytokines, perforins, granzymes, interferon gamma
and tumour necrosis factor in the vicinity of cells carrying intracellular pathogens.5. Cytotoxic chemicals/cytokines cause target cell destruction.
Table 15.3: Comparing Attributes of Humoral and Cellular Immunity
APPLICATION 15.1
1.Complete with appropriate terms:
(i) ............... is the type of antibody produced by primary immune response.
(ii) Cell mediated immunity is achieved by ......................
(iii) Antibody .................... is highly mobile and capable of reaching skin to neutralize
bacteria.
(iv) ................ immunity leads to auto-immune disease.
2.What is the difference between T helper and T killer cells?
3. What is the role of the memory cells?
4.Explain how herd vaccination could be used to protect us from bird flu
5. Explain the difference between antigens and antibodies
6. a) Explain what is meant by clonal selection during the immune response
b) How are antibodies made specific to the antigen?
c) Apart from specificity, describe how the structure of an antibody molecule is suited to its
function
7. a) What is the difference between passive immunity and active immunity?
b) Explain what is meant by an attenuated pathogenc) Describe how an attenuated pathogen could be used to create artificial active immunity
ACTIVITY 2
Using different colours, learners can make flow diagram of immune response following
infection by a toxin/bacteria in the extracellular fluid and also a flow chart of immune response
following infection by bacteria such as Mycobacteria.
In these flow charts, draw different cell types participating in the immune response, and show
all the steps which ultimately lead to clearence of the pathogen.
Discuss the following questions to clarify major immune mechanisms of the body.
(i) How does humoral branch of immunity recognize the pathogen?
(ii) How does cell mediated branch of immunity recognize the pathogen?
(iii) How are the two branches interconnected?(iv) How are these two branches connected with innate immunity?
15.2 VACCINATION
ACTIVITY 3
Collect data of various diseases affecting a population such as smallpox, measles, malaria and
tuberculosis. You can collect data from health centres, or hospitals. Make a point of collecting
data before and after the vaccination provided in the same population.
Discuss the findings of different groups to assess whether vaccination programme has been
equally successful for all the diseases or not.Discuss why vaccination strategy has not worked against certain diseases.
While looking for answers for the above mentioned questions, you would have realized that
in the past 40 years immunization against a number of diseases has saved millions of lives.
World Polio Day is celebrated every year on 24th October, World Tuberculosis Day falls on
24th March every year, and World Immunization Week is observed by WHO from 24th to
30th April every year to have campaigns for awareness of the importance of vaccination in
eradicating these debilitating diseases as well as to provide vaccinations worldwide.
Success of immunization programmes is evident by the facts such as: Small pox has been
globally eradicated; Africa has not had a case of wild poliovirus since August 2014; India has
been declared free of maternal and neonatal tatanus; during 2000–2014, measles vaccination
prevented nearly 17.1 million deaths (decreaing deaths by 79%); deaths caused by tuberculosis
have come down only marginally.
The pioneering work of Jenner and Pasteur laid the foundations of immunization
programmes. They were able to confer protection to individuals against infectious diseases
by exposing them to infectious agents. This initiated the process of active immunization
in the medical field and saved millions of lives. However, the works of Kitasato showed
that immunity can be transferred between two individuals, and this laid the foundation
of passive immunization programmes. Though both these programmes confer protection
against infectious agents, there are important differences between the two (as shown inTable 15.4).
Table 15.4: Comparing Active and Passive Immunization
ACTIVITY 4
Find out National Immunization Days for tuberculosis, measles, and cholera. Search medical
journals to find out symptoms of these diseases and discuss in the class as to what role you canplay to promote awareness campaigns.
Though smallpox has been successfully eradicated, eradication of others such as measles,
tuberculosis, cholera and malaria has not been so successful. Success of smallpox vaccine
was due mainly to the fact that pox virus did not mutate and the same vaccine could be used
everywhere and the vaccine was highly effective.
On the other hand, though measles vaccination has decreased death rates drastically, its total
eradication has not been achieved so far due to several reasons. The disease is highly infectious,
and spreads very fast. As long as it is present in one area, unvaccinated children in any country
are at risk. For measles, boosters are required, difficult to achieve in poor countries, Parents’
decision not to vaccinate their children due to fear or other misconceived notions has also madethe vaccination programme less effective.
Effective vaccine against cholera has not been available for two major reasons: (a) Immunity
conferred by the vaccine is not long-lasting; (b) Cholera is a toxin-mediated disease while
protective immune mechanism is antibacterial rather than antitoxic. Oral cholera vaccines
have become available recently.
Tuberculosis is a major killer, causing 2 to 3 million deaths annually. According to WHO
reports, nearly one-third of the world’s population is currently infected with TB. Today, the
only approved tuberculosis vaccine is Bacilli Calmette-Guerin (BCG) which was started
in 1921. Though it is quite effective in infants and young children, in adults, its efficacy is
variable. Many boosters are also being developed, MVA85A, being the most advanced boost
available. BCG vaccine has not been modified since 1921 and that may also be one reason
why it is not so effective. That bacteria may have changed through evolution is suggested
by their evolution of resistance to a number of known antibiotics. A lot of effort is being
devoted, but proving difficult as the bacterium lives within the cells and lack of suitable animal
model for developing and testing human tuberculosis vaccine is posing a big challenge. In
Africa, coinfections of human immunodeficiency virus and TB have led to increases in theincidence rate of TB.
Malarial parasite lives intracellularly and mutates very often to change surface antigens andthus proved very difficult organism for effective vaccine development.
15.3 ALLERGIES
ACTIVITY 5
Watch one video of a person with watery eyes, running nose, sneezing; another with an
asthmatic person with breathing problems and using inhaler; another with a person stung by a
bee, showing swelling and redness.
Collect labels on certain food items prepared from shellfish/peanuts/walnuts/showing warning
to individuals.
See labels on penicillin vials, as a warning to be used only after initial testing.
After having seen these, try to answer the following:
(a) Why should some persons show watery eyes, running nose or asthmatic symptoms when
there is nothing alarming in the environment?
(b) Why should common food items be a cause of worry?(c) Why can’t we use penicillin just as we use any other antibiotic?
Allergic reactions are seen when humoral or cell-mediated immune responses to non-parasitic,
non-pathogenic substances lead to extensive damage of tissues in individuals prone to
allergies or hypersensitive reactions. Hypersensitive responses are classified into four types
(Figure 15.5).
1. IgE-mediated (Type I)
2. IgG or IgM-mediated (Type II)
3. Immune complexes (Type III)4. Cell-mediated (Type IV)
Figure 15.5: Showing different types of hypersensitive responses
IgE-mediated (Type I) Hypersensitivity: First exposure to allergen leads to the formation of
IgE type of antibodies which bind to mast cells present in large numbers throughout the body.
Second exposure to the same allergen causes cross-linking of IgE molecules on the already
sensitized mast cells, leading to their degranulation and release of substances stored in their
granules such as histamine, heparin, proteases, etc. Principal effects seen are vasodilation and
smooth muscle contraction (Figure 15.6). Vasodilation decreases blood pressure and contractionof smooth muscles of bronchioles affects respiration.
Figure 15.6: Showing type I hypersensitive reaction
Generalized allergic reaction, called anaphylaxis, starts when an allergen enters directly into
the bloodstream or is absorbed from the gut or skin. It can be caused by venom from bee, wasp,
ant stings; drugs such as penicillin, antitoxins. This should be treated quickly; otherwise it is
shock-like and often fatal.
In localized allergic reaction, the damage is limited to a specific target tissue or organ. Examples
include allergic rhinitis (hay fever), asthma, dermatitis, food allergies.
Hay fever occurs upon inhaling certain allergens in the air leading to watery eyes, running nose,
sneezing and coughing, involving mainly upper respiratory tract.
Asthma involves lower respiratory tract when histamine released from mast cells causes
contraction of bronchioles. Mucus accumulates in the air sacs, causing respiratory problems
and the characteristic wheezing sound. It can prove fatal if left untreated for too long.
Allergens, generally responsible for this reaction, are pollens, dust, fumes, insect products,
or viral antigens.
Epinephrine helps in generalized reaction by relaxing the smooth muscles for respiration to
restore and reducing vascular permeability so that blood pressure can normalize improvingcardiac output. Antihistamines are used to relieve the symptoms of asthma and hay fever.
Table 15.5: Distinction between Generalized and Localized Allergic Reactions
IgG or IgM-mediated (Type II) Hypersensitivity occurs when antigen-antibody complex
activates complement proteins which can cause rupture of cells. This is seen in blood transfusion
reactions.
Immune complexes (Type III) deposited in tissues lead to complement activation and
inflammation. This is seen after insect bites as swelling and reddening locally or in serum
sickness as fever and shivering after receiving anti-tetanus anti-toxin.
Cell-mediated (Type IV) Hypersensitivity is mediated by helper T lymphocytes and macrophagesas in contact dermatitis and graft rejection.
Important Message
Having read this section on hypersensitivity, can you visualize how you would go about helpingone of your classmates showing such symptoms
15.4 ANTIBIOTICS
ACTIVITY 6
Collect data on diseases and their antibiotics. Make a table to present your research. Once you
are done, discuss the following questions:
(i) How bacteria have acquired resistance against the antibiotic over the years.
(ii) Comment on the efficacy of antibiotics in treating a certain disease when the antibiotic for
the disease was first discovered.
Note: Some of the diseases which can be investigated are: Dysentry, Tuberculosis, Pneumonia,Diphtheria, Cholera, Measles, Mumps, Smallpox.
The word ‘antibiotics’ is derived from the Greek word “anti” meaning against and “bios”
life. Antibiotics are a class of chemicals produced by bacteria or fungi in order to inhibit the
growth of other organisms in their vicinity so that competition for limited resources can be
minimized. The first antibiotic, penicillin, was discovered by Alexander Fleming in 1928. Since
then antibiotics have found great use in medicine. Though they are not effective against viruses,
they are used to treat a number of bacterial infections.
A large number of antibiotics have been discovered from a variety of organisms, broadly
belonging to two categories: bactericidal, which kill the bacteria and bacteriostatic, which slow
down their growth and reproduction. Bactericidal antibiotics prevent the formation of cell wall
while bacteriostatic antibiotics interfere with some aspect of bacterial metabolism, affecting
either protein or RNA synthesis or DNA replication. They must work together with the immune
system to remove microorganisms from the body. High concentrations may also be bactericidal.
Table 15.6 shows a few commonly used antibiotics, source organisms producing them and theiractivity. Figure 15.7 shows mode of action of some antibiotics.
Table 15.6: Types of Antibiotics
Figure 15.7: Mode of action of antibiotics
As the use of antibiotics has increased, it has also led to the evolution of resistance in a number
of microbial pathogens with the result that earlier antibiotics are no longer effective in treating
a disease. Resistance may have developed by a number of mechanisms e.g.,
1. Production of enzyme beta lactamase that breaks down beta- lactam ring of antibiotics
such as penicillin and cephalosporin.
2. Mutation in a gene leading to the formation of an altered protein which does not bind
penicillin.
3. Altered cell wall permeability confers resistance to tetracyclines, quinolones, penicillin.
4. Creating a barrier of biofilm, where bacteria are not attacked by the host’s immune system
as seen in Salmonella.
5. A gene can produce a product that can pump out the antibiotic as in Staphylococcus
against erythromycin.
6. Some bacteria show alteration in ribosome structure so that protein synthesis is notaffected.
APPLICATION 15.2
1.Complete with appropriate terms:
(i) ................. leads to production of long lived memory cells.
(ii) Cholera is a ................. mediated disease.
(iii) .................... decreases blood pressure and contraction of muscles of bronchiols.
(iv) ............... occurs upon inhaling certain allergens in the air leading to sneezing and
coughing.
(v) Penicillin is produced by ....................................
2. Two people took part in a study to find out the effectiveness of two types of immunization.
Person A received an injection of antibodies against tetanus and person B receive a tetanus
vaccination. Over the next few weeks, the blood from these two people was analyzed forthe presence of antibodies to tetanus. The results are shown in the figure 1A and figure 1B.
Figure 1A
Figure 1B
a) Name the types of immunity shown by figures 1A and 1B.
b) Explain why the antibody concentration in person A,
i. Decreased during the study period
ii. Did not increase
c) Sketch on a copy of figure 1B what you would expect to happen to the antibody concentration
if person B received a booster vaccination at day 60.
d) Explain why in this investigation, the experimenters had to measure the concentration ofantibodies to tetanus rather than the concentration of all antibodies in the blood of A and B.
ACTIVITY 7
Using internet sources and medical journals, try to find out the following:
(i) Mortality caused by tuberculosis, measles, small pox and cholera.
(ii) How has medical science helped in reducing death rate caused by these diseases?
(iii) Has it been completely successful in this effort?
(iv) What role does nutrition play in fighting these diseases?
(v) Role of water and sanitation services in controlling spread of disease.
15.5 SUMMARY
• Immune system has the capacity to kill cells, it is very important for it to make a distinction
between self and non-self.
• Whenever there is a failure in distinguishing self from non-self, auto-immune diseases
develop such as multiple sclerosis, rheumatoid arthritis.
• Mounting of a successful immune response depends on a number of cells and chemical
mediators, defect in any component can lead to immunodeficiency state such as absence
of mature T lymphocytes in Di George syndrome.
• Immune system has two main parts, innate and adaptive.
• Two branches of the immune system collaborate with each other to make a highly
effective immune response.
• Innate system is present at birth, comes into operation immediately upon infection,
relies on barriers such as skin and mucous membranes, phagocytes and NK cells,
and lacks memory.
• Adaptive system is acquired by 6 months after birth, takes time to mount an immune
response, relies on B and T lymphocytes and has memory.
• Adaptive or acquired immunity is of two types, humoral and cell mediated.
• Humoral immunity generates specific antibodies against pathogens present in blood.
• Cell mediated immunity generates cyto-toxic chemicals to lyse infected cells.
• Antibodies neutralize toxins and help in eliminating microbial organisms.
• Antibodies are of five types IgM, IgG, IgA, IgE and IgD.
• There are two types of T lymphocytes: helper T lymphocytes and Tc lymphocytes.
• T lymphocytes recognize antigen of the pathogen in association with MHC.
• Helper T lymphocytes actively secrete a number of cytokines which affect the activity of
macrophages, B lymphocytes and Tc cells converting the latter into CTL.
• CTLs, macrophages and NK cells secrete cytotoxic chemicals onto cells having intracellular
pathogen causing cell death.
• Vaccinations can be Active or Passive.
• Active vaccination is achieved either by natural infection or by immunization with live
attenuated or killed infectious organisms.
• Passive immunization is achieved by introduction of preformed antibodies.
• Generation of memory cells during first encounter with the infectious agent produces a
secondary response with a high intensity.
• Vaccination programmes for a number of diseases have been very successful, though for
some diseases, effective vaccines are not available yet.
• Although active vaccines have helped eradicate a number of diseases, they pose a serious
threat in immuno deficient individuals.
• Passive immunization is chosen in cases of emergency or immunodeficiency.
• Allergies, also termed hypersensitive responses, which are potentially damaging to
the tissues, are produced by the body to seemingly non-pathogenic substances in the
environment.
• Allergies are broadly classified into four types: class I mediated by IgE; class II mediated
by IgG or IgM; class III by activation of complement by immune complexes; class IV
cell mediated (esp. macrophages ) hypersensitivity.
• Type I allergies are seen in hay fever, asthma, food allergies; type II allergies are seen in
blood transfusion reactions; type III allergies seen after insect bite or serum sickness
after anti-tetanus injection; type IV allergies seen in contact dermatitis, graft rejection.
• When the hypersensitive reactions are limited to specific target tissue or organ, it is called
localized reaction as seen in hay fever, asthma. However, when a large number of organs
become simultaneously affected upon entry of allergen directly into the bloodstream
absorbed from the gut, it results in generalized reaction with fatal consequences.
Symptoms and treatment
• Type I hypersensitive reactions are mediated by heparin released by mast cells and
epinephrine can reverse these effects in generalized reactions while antihistamines are
used for localized reactions.
• In all other cases of allergies involving drug, food item, blood transfusion, anti-toxin
antiserum,
the best strategy is to immediately discontinue the use of such agents.
• Antibiotics are drugs used extensively by doctors to treat bacterial infections. Mortality
rate due to bacterial infections has declined drastically since the use of antibiotics started.
• A number of soil microbes produce a large variety of chemicals to inhibit other organisms
growing in their surroundings and provide a rich source of antibiotics.
• Antibiotics either kill bacteria by inhibiting their cell wall synthesis or slowing their
growth by affecting DNA replication or RNA/ protein synthesis.
• Different antibiotics show different specificities, some antibiotics working against a
number of bacteria, while others being more specific.
• Prolonged and overuse of antibiotics has led to evolution of different mechanisms by
which bacteria have become resistant to commonly used antibiotics such as development
of enzyme beta lactamase to break down beta lactam ring, actively move the drug outof the cell (efflux), change its cell wall permeability etc.
15.6 GLOSSARY
• Acquired immunity: It is the immunity that our body gains over time, similar to how an
individual gains knowledge over time.
• Antibiotics: Substance that destroys or inhibits the growth of other microorganisms.
• Antigen: A substance that your immune system reacts against.
• Cellular immunity: It is an immune response that does not involve antibiotics but rather
in values the activation of phagocytes, antigen specific T-lymphocytes.
• Humoral immunity: Immunity involving the transformation of B-lymphocytes into
plasma cells that produce and antibiotics to a specific antigen.
• Immune response: The reaction of the cells and fluids of the body to the presence of a
substance which is not recognised as a constituent of the body itself.
• Immunity: It is the defence mechanism of our body.
• Innate immunity: Immunity that is naturally present and is not due to prior mustization
to an antigen form.
• Vaccination: Injection of a killed microbe in order to stimulate the immune systemagainst the microbe, thereby preventing disease.
END UNIT ASSESSMENT 15
I. Choose whether the given statements are True (T) or False (F)
1. Innate immunity is present at birth.
2. Breast milk confers protection to newborn by providing IgE type of antibodies.
3. Antibodies can work by promoting phagocytosis of microbial agents.
4. Antibiotics help a patient in mounting an effective immune response.
5. Treating tuberculosis is becoming difficult because Mycobacterium tuberculosis has
become resistant to a number of antibiotics.
6. Hay fever is a generalized allergic reaction caused by release of active mediators from
mast cells.
7. Secondary immune response appears much faster because of the presence of memory
cells persisting from previous infection.
8. Vaccination against snakebite is an example of passive immunization.
9. Allergies are of two types—innate and adaptive.
10. Beta-lactam antibiotics kill bacteria by blocking synthesis of their cell walls.
II. Multiple Choice Questions1. Humoral immunity is carried out by the
(a) B lymphocytes (b) T lymphocytes
(c) Phagocytes (d) T lymphocytes, phagocytes and NK cells
2. Antibodies transferred across placenta to the developing embryo are
(a) IgM (b) IgG
(c) IgA (d) IgE
3. Plasma cells represent
(a) B lymphocytes which are actively secreting antibodies.
(b) T lymphocytes which are actively secreting cytokines
(c) Monocytes which have entered tissues
(d) CTL which are secreting perforins.
4. Mast cell degranulation leads to the release of
(a) IgE, which causes vasodilatation and bronchoconstriction
(b) IgE, which causes vasoconstriction and bronchodilation.
(c) Histamine, which causes vasodilation and bronchoconstriction
(d) Histamine, which causes vasoconstriction and bronchodilation
5. Tetracycline helps in treating respiratory tract infections by
(a) preventing protein synthesis in influenza viruses
(b) preventing protein synthesis in bacteria
(c) preventing DNA repair in viruses
(d) preventing cell wall synthesis in bacteria
6. Children born with Di George syndrome lack mature
(a) B lymphocytes (b) T lymphocytes
(c) Macrophages (d) NK cells
7. Faulty recognition of self-tissues as non-self leads to the development of(a) AIDS (b) Rheumatoid arthritis
(c) Hay fever (d) Polio
8. Live attenuated vaccine types have the disadvantage over the inactivated vaccine types
as
(a) They require booster shots
(b) They do not confer life-long immunity
(c) They may mutate to virulent form
(d) They do not stimulate the immune system strongly.
9. Immune response is
(a) the defence mechanism of our body.
(b) reaction of the cells and fluids of the body.
(c) a substance that destroys or inhibits the growth of other microorganisms
(d) None of the above
10. Nowadays, many antibiotics don’t seem to work because
(a) body starts degrading the antibiotics very rapidly
(b) of increased levels of pollution
(c) bacteria are rapidly evolving resistance to antibiotics already in use
(d) pharmaceutical companies are not making good medicines now.
III. Long Answer Type Questions
1. With an illustrative diagram, state the origin and describe the mode of action of
phagocytes.
2. Analyse and relate the molecular structure of antibodies to their functions. Also,
state the role of antibodies in allergies.
3. Explain the following:
(a) Phagocytes
(b) Lymphocytes
(c) Immune response
4. Compare giving diagrams the modes of action of B-lymphocyte and T-lymphocyte.
5. With examples, explain the role of memory cells in long-term immunity.
6. Differentiate between the following:
(a) Active and passive immunity
(b) Generalised and localised allergic reactions
7. Discuss causes, symptoms and treatment of asthma and hey fever. Also suggest the
ways to encourage such patients.
8. State why vaccination programmes are able to eradicate smallpox but not measles,
TB, malaria or cholera.
9. Define antibiotic. State how it works. Also, explain the reasons for antibiotic
resistance.
10. Interpret the differences between cellular responses and humoral responses.
11. Carry out research and be able to present findings on the reasons for antibiotic
resistance in the treatment of infections.
12. There is a lot of research for curing diseases around the globe. Discuss the plausible
research going on for HIV AIDS. Also state the bodies immune response condition
while tackling HIV.