the immunological response

8/2/2019 The Immunological Response

http://slidepdf.com/reader/full/the-immunological-response 1/3

THE IMMUNOLOGICAL RESPONSE

It results from the introduction of an Ag into the body . The immune

response may be :

1. Non-specific : as inflammation and phagocytosis.

2. Specific or adaptive : and this may be humoral or cellular.

The specific immune Response :

Cells involved in the specific immune response :

1.Macrophages

They are phagocytic cells which are mainly concerned with

processing and presentation of the Ags to the lymphocytes and so they

are called the antigen presenting cells . They can also secrete cytokines

e.g. interleukin-1 (IL-1).

2.Lymphocytes

They originate from a stem cell in the bone marrow and they

include:

- T-lymphocytes or T-cells which mature in the microenviroment of

the thymus, They are responsible for the cell-mediated immunity.T-cells

can be subdivided into :

- Helper/inducer subsets (CD4 + Cells)

- Suppressor/cytotoxic subsets (CD4 + Cells)

- B-lymphocytes or B-cells which mature in the bone marrow anddo not pass by the thymus . They are responsible for the humoral

immunity



The major events taking place in the specific immune response are:

1.Antigen processing and presentation

The antigen presenting cell (e.g. macrophage) takes up the foreign

antigen, internalizes it, and breaks it into small fragments, thenpresents it in a simple form on its surface complexed with MHC class II

molecule to be recognized by the receptor on the surface of the specific

T-helper cell .The macrophage also secretes IL-T which activates the T-

helper cell.

Other cells can also act as antigen presenting cells such as Langerhans

cells of the skin, dendritic cells , and B lymphocytes.

2.Activation of the T-helper cell

The T-helper cell is activated when it recognizes its specific

antigen presented to it by the antigen presenting cell and also by the

cytokines produced by the macrophage , It undergoes proliferation and

produces a number of cytokines (e.g. IL-2,IL-4 and IL-6 ) which act on

other cells of the immune system as T-cytotoxic cells , B-cells and

macrophages causing their proliferation and activation.

3.Activation of T-cytotoxic cells

T-cytotoxic cells become activated when they recognize their

antigen on the surface of a target cell , complexed with MHC class I

moleculeand also by the effect of cyto kines produced by the activated

T-helper cell . The activated T-cytotoxic cell then releases cytotoxins

which kill the target cell e.g. virus-infected , tumour cell. This represents

the cellular or cell-mediated immune response.

4.Activation of B-cells

When B-cells recognize their specific antigen by surface

membrane Ig receptors , and are acted upon by the cytokines released

by the activated T-helper cells, thei will become activated and will



undergo proliferation and differentiation into antibody producing

plasma cells . these cells will secrete antibodies specific to the antigen

which induced the reponse . These antibodies can lyse bacteria or

prepare them for phagocytosis by osponisation , they can neutralizetoxins and can neutralize viruses rendering them non-effective . This

represents the humoral or antibody-mediated immune response.

5.Some activated B and T-cells become MEMORY CELLS which can

respond to subsequent encounters with the same antigen .

6. The usual outcome of the immune response is the ELIMINATION OF

THE OFFENDING ANTIGEN . After that the response is down-regulated

by suppressor T-cells to prevent unnecessary activation of lymphocytes

and unregulated production of antibodies .

the immunological response

Documents