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Before an invading microbe can be eliminated form the body by the immune system these steps must take place: 1 .A macro'phage is activated to phagocytize the

• ffending

particle and present antigen to T and B lymphocytes.

• 2. Activated

T -cells synthesize and secrete . cytokine.

• 3. B- cells are activated

bya T -cell cytokine and antigen from a pathogen. .

• 4. Activated

B-cells may become either a plasma cell or a B-memory cell.

• 5. Plasma

cells synthesize and secrete immunoglobin.

• 6. Immunologic

memory is established when specific B-memory cells and T- cells form a specific clone dedicated to protecting the body against a specific antigen.

• 7. Acquired

immunity is very effective but takes days

• r weeks

to establish. The presence

• f a

specific immunity clone reduces the time from pathogenic challenge to protection .

The structure of the receptor for T cells.

• Fig. 15.6 Proposed structure of the T cell receptor for antigen.

The Class I and II MHC for humans are surface receptors consisting of glycoproteins.

• Fig. 15.2 The human major histocompatibility complex.

Characteristics of the different subsets of T cells. Table 15.3 Characteristic of subsets of T cells.

The stages of B-cell activation and antibody synthesis.

• Fig. 15.10 Events in B-cell activation and antibody synthesis.

Run Animation: Antibody diversity

An example of helper and cytotoxic T cell activation and differentiation.

• Fig. 15.16 Overall scheme of T-cell activation and

differentiation into different types of T cells.

An example of a cytotoxic T cell destroying a cancer cell.

• Fig. 15.17 A cytotoxic T cell has mounted a successful

attack on a tumor cell.