Download IMMUNE SYSTEM

IMMUNE SYSTEM
OVERVIEW
Lecture – 9
Dr. Zahoor
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OBJECTIVE
You should know
• About innate and adaptive immunity
• Self tolerance
• Immune surveillance
• Auto immune diseases
• Transplant rejection
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IMMUNE SYSTEM
What is the function of Immune System?
• To defend the body against foreign invaders (bacteria, virus) and
cancer cells
• Immune System recognizes the normal body cells and destroys the
material that are not “normal self”
• Immune response can lead to allergic reaction or auto-immune
diseases (anti-bodies against body’s own cell)
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IMMUNE SYSTEM
• Leukocytes are effecter cells of immune system
• We have discussed Neutrophils, Eosinophils, Basophiles, Monocyte
• Most important part played in the Immune System is by Lymphocytes
1. B-Lymphocyte – Antibody mediated immunity
2. T-Lymphocyte – Cell mediated immunity
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IMMUNE SYSTEM
Lymphocyte
• Originally derived from bone marrow, but later they arise from
lymphoid tissue
What is Lymphoid Tissue?
• Lymphoid Tissue include bone marrow, lymph node, spleen, thymus,
tonsils, appendix and lymphoid tissue in the lining of digestive tract
called Peyer’s Patches
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IMMUNE SYSTEM
• Bone marrow process B-Lymphocyte
• Thymus process T-Lymphocyte
• Lymphoid tissue produces, stores, and process lymphocytes in adults
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IMMUNE RESPONSE
 They are of two types of Immune Response:
1. Innate or Inborn – non specific
2. Adaptive or Acquired – specific
1. Innate or Inborn Immunity
 It is natural, inherent defense mechanism
 It is non-selective
 It comes into play on exposure to foreign or abnormal material
e.g. infectious agent, chemical irritants
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Innate or Inborn Immunity
• Innate immunity is done by
- Neutrophil
- Macrophages
- Plasma protein_ Complement system
_ Dendritic cells
_ Natural killer cells
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Innate or Inborn Immunity
- Body defends itself against invading organism by
1- Inflammation – it is response by the body to tissue injury in which
Neutrophil and macrophages play role
2- Interferon – a family of protein that defend the body against viral
infection
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Innate or Inborn Immunity
3- Natural Killer cells – Lymphocyte like cells that cause destruction of
viral infected cells and cancer cells
4- Complement System – it is group of inactive plasma proteins, when
activated bring destruction of foreign cells by attacking their plasma
membrane
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IMMUNE RESPONSE
2. Adaptive or Acquired
• It is specific
• It is response by the body against a particular foreign material
• It is mediated by T-Lymphocyte and
B-Lymphocyte
• Each B and T Lymphocyte can recognize and defend against one type
of foreign material e.g. bacteria
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Adaptive or Acquired Immunity
• There are millions of B and T Lymphocytes
• One type of cells (clone) are called against one agent
• It is selective attack to limit the pathogen
• It is done by antibody mediated immunity and cell mediated
immunity
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Adaptive or Acquired Immunity
• B-cells recognize bacteria and few viruses and they respond by
producing antibodies which are specific for the invader
• T-cell recognize virus infected cells and cancer cells
• Each of us has about 2 trillion lymphocytes, they remain on constant
surveillance
Both Innate and Adaptive Immunity work together
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Innate Vs. Adaptive Immunity
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TISSUE TRANSPLANT
Why tissue transplant is rejected?
• Tissue transplant is rejected because T-cell bind with MHC (Major
Histocompatibility Complex) antigens present on the surface of
transplanted cells and trigger the rejection of transplanted or grafted
tissues
• To minimize the rejection phenomenon, tissue of donor and recipient
are matched according to MHC antigens as closely as possible
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TISSUE TRANSPLANT
How to prevent tissue transplant rejection?
• Drugs are given to suppress the immune response
• Before immunosuppressive therapy included
- Radiotherapy and drugs given to destroy lymphocytes
- That treatment affected both T and B cells, therefore, immune
protection was lost against bacteria and virus
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TISSUE TRANSPLANT
• In recent years, new treatment is aimed at selectively suppressing Tcells mediated immune activity, while leaving B-cell antibody
immunity intact e.g. Cyclosporin
How Cyclosporin acts?
• It blocks IL-2 which is secreted by T-helper Lymphocytes to help
cytotoxic T-cells
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TISSUE TRANSPLANT
Future therapy
• New methods are under investigation which may prevent rejection of
unmatched donor.
How ?
By giving antibodies that block specific process involved in rejection.
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SELF TOLERANCE
Why Immune System is tolerant to self that it
does not attack persons own tissues?
 Because during development of lymphocyte, immune system does
not produce antibodies or activated T-lymphocytes against body’s
own self antigen
 At least 8 different mechanism are involved in tolerance
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DIFFERENT MECHANISM INVOLVED IN
TOLERANCE
1- Clonal Deletion
• B and T Lymphocyte clones which are capable of attacking self
antigens are destroyed in the thymus
2- Clonal anergy (loss of energy)
• T-Lymphocyte which work against self are inactivated by body
antigen
3- Receptor Editing
• B-cells receptors encounter body antigen and never target them
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DIFFERENT MECHANISM INVOLVED IN
TOLERANCE
4- Active suppression by regulator or suppressor T-cell
• Suppressor T-cell help in tolerance
5- Some antigen are hidden from immune system e.g. thyroglobulin
in thyroid gland and they never come in direct contact with immune
cells
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DIFFERENT MECHANISM INVOLVED IN
TOLERANCE
6- Immune Privilege
• Eye cornea transplant escape immune attack even when
transplanted from unrelated person
Why?
 It is discovered that plasma membrane in these tissues have
molecule that triggers the Apoptosis of Lymphocyte that attack these
tissues
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DIFFERENT MECHANISM INVOLVED IN
TOLERANCE
7- Activation induced cell death of B-cells
8- Release of IL-10 by T-helper, cytotoxic T-cell, B-cell
• IL-10 is cytokine that inhibits macrophage and dendritic cells which
are Antigen Presenting Cells (APCs)
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AUTO IMMUNE DISEASES
What is Auto Immune Disease?
• Loss of tolerance to self antigen, therefore, there is auto immune
disease (auto means against self)
Why it occurs?
It is due to combination of genetic and environmental factors e.g.
modification by virus, drugs, bacteria
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AUTO IMMUNE DISEASES
 There are more than 80 auto immune diseases
 Few examples
- Type 1 Diabetes Mellitus
- Rheumatoid Arthritis
- SLE
- Thyroid Disease
 Auto immune disease is three times more common in female
than male
 Auto immune disease affects 1 in 20 people world wide
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EXTERNAL DEFENSES OF THE BODY
1.
2.
3.
4.
Skin – outer protective epidermis and inner connective tissue
dermis
Defenses of the digestive system
Defenses of the respiratory system
Defenses of the urogenital system
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APPLIED
 Cigarette smoking suppresses the normal respiratory defenses. It
affects movements of cilia in respiratory system, it affects function of
alveolar macrophage
 It has toxic effect on lung tissue and there is increased incidence of
chronic respiratory diseases and lung cancer
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Thank you
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