Role of T Cells in Immune Responses

Published on 18/02/2015 by admin

Filed under Allergy and Immunology

Last modified 18/02/2015

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Chapter 2

Role of T Cells in Immune Responses

T Cell Surface Molecules

T cell receptor (TCR) complex

• Comprises an antigen-recognizing heterodimer associated with a multimeric activation unit (CD3) (Box 2-1; Fig. 2-1)

Accessory molecules

II Development and Activation of T Cells

Antigen-independent maturation

Antigen-dependent activation

1. Leads to proliferation and differentiation of naive T cells (clonal expansion) into effector cells and memory T cells (Fig. 2-2)

2. Effective stimulation requires primary and coactivating signals (fail-safe mechanism) that trigger intracellular signal transduction cascades, ultimately resulting in new gene expression (Fig. 2-3).

3. Signal 3 (determines nature of response): direction—cytokine from dendritic cell (DC) or APC

4. Adhesion molecules: selectin (E-, L-, P-), ICAM (-1, -2, -3, LFA-3 CD2), and integrin (VLA, LFA-1, CR3)

Antigen processing and presentation by class I and II MHC molecules (Fig. 2-4)

• Different pathways are used for degradation of intracellular and internalized extracellular protein trash. Peptides resulting from digestion of nonhost (foreign) protein trash are recognized by the T cell surveillance squad, which mounts an appropriate defense (Box 2-2).