The Immune System

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Lymphocytes with receptors specific for the body’s own molecules are destroyed by apoptosis, or rendered nonfunctional.

Slide 36

Amplifying Lymphocytes by Clonal Selection

In the body there are few lymphocytes with antigen receptors for any particular epitope.

The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly.

This proliferation of lymphocytes is called clonal selection.

Two types of clones are produced: short-lived activated effector cells (fight current battle) and long-lived memory cells… for future attacks by same pathogen.

Slide 37

Clonal Selection of B cells

B cells that

differ in

antigen

specificity

Antibody

molecules

Antigen

receptor

Antigen molecules

Clone of memory cells

Clone of plasma cells = effectors

Slide 38

The first exposure to a specific antigen represents the primary immune response.

During this time, effector B cells = plasma cells are generated, and T cells are activated to their effector forms.

In the secondary immune response = memory cells facilitate a faster, more efficient response.

Slide 39

Antibodies

to A

Antibodies

to B

Secondary immune response to

antigen A produces antibodies to A.

Primary immune response to antigen

B produces antibodies to B.

Primary immune response

to antigen A produces

antibodies to A.

Antibody concentration

(arbitrary units)

Exposure

to antigen A

Exposure to

antigens A and B

Time (days)

104

103

102

101

100

0

7

14

21

28

35

42

49

56

Slide 40

Acquired immunity defends against infection of body cells and fluids

Acquired immunity has two branches: the humoral immune response and the cell-mediated immune response.

Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies.

Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells.

Helper T cells aid both responses.

Slide 41

Acquired Immune Response

Humoral (antibody-mediated) immune response

B cell

Plasma cells

Cell-mediated immune response

Key

Stimulates

Gives rise to

+

+

+

+

+

+

+

Memory B cells

Antigen (1st exposure)

Engulfed by

Antigen-