Acquired Immunity

Posted by e-Medical PPT
Defensive mechanisms include :
1) Innate immunity (Natural or Non specific)
2) Acquired immunity (Adaptive or Specific)
Cell-mediated immunity
Humoral immunity
Aquired (specific) immunity
* The acquired immune response is more specialized
than innate immune response
* The acquired immune response involves a combination
of two mechanisms :
1) Humoral immune response
2) cell mediated immune response
* They interact with one another to destroy foreign body
(microorganisms, infected cells, tumor cells)

Two mechanisms
1) Humoral immune response:
- Antibodies are produced by B-lymphocytes
- These have the ability to recognize and bind
specifically to antigen that induced their formation

2) The cell mediated immune response (CMI)
- It is mediated by certain types of T-lymphocytes
- T-lymphocytes recognize foreign material by
means of surface receptors
- T-lymphocytes attack and destroy foreign material
directly or through release of soluble mediators
i.e. cytokines

Characters Of Acquired Immune Response
1) Highly specific for the invading organism

2) Discrimination between “self and “non self” molecules
The response only occurs to “non self” molecules

3) Diversity:
- It can respond to millions of different antigens
- Lymphoctes population consists of many different clones (one cell and its progny)
- Each clone express an antigen receptor and responds only to one antigenic epitope

Mechanism Of Acquired Immune Response
Acquired immune response is initiated by:
* Recognition of the antigen by specific lymphocytes
* Activation of these specific lymphocytes
* Proliferation and differentiation into effector cells;
-The effector cells eliminate the antigen
-Return of homeostasis and development of memory cells
* Memory cells evoke a more rapid and long response on re-exposure to same antigen

Mechanism of Humoral immunity
Antibodies induce resistance through:
1) Antitoxin neutralize bacterial toxins (diphtheria,tetanus)
Antitoxin are developed actively as a result of:
a- Previous infection
b- Artificial immunization
c- Transferred passively as antiserum
* Neutralization of toxin with antitoxin prevents a combination with tissue cells

2) Antibodies attach to the surface of bacteria and
a- act as opsonins and enhance phagocytosisd
b- prevent the adherence of microorganisms to
their target cells, e.g. IgA in the gut
c- Activate the complement and lead to bacterial lysis
d- Clump bacteria (agglutination) leading to

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