IMMUNOLOGY - Roitt I. - Mir 2000

Chapter 9. Antigen Recognition

T-CELL ANTIGEN RECOGNITION

T Cells recognize Antigens that are Cell-bound and presented On the surface of other cells in association (complex) with MHC Class I or II molecules, which function as 'homing devices' for T cells. This requirement for association with MHC molecules is known as MHC restriction. THE PRINCIPLE OF such restriction is most clearly demonstrated in the T-cell Immune Response to experimental viral infection in the mouse (Fig. 9.17). Cytotoxic T lymphocytes (Tc) from an infected animal can lyse virus-infected target Cells of the same H-2 haplotype, but not those of a different haplotype.

Fig. 9.17. Haplotype-restricted killing of virus-infected target cells by cytotoxic T lymphocytes (Tc). Mice of the H-2b haplotype were primed with virus, after which Tc were isolated from the Spleen and tested for their ability to lyse virus-infected target cells of H-2b and H-2k haplotypes. The Tc lyse H-2b target cells, but not H-2k ones, i. e. T cells recognize a specific Structure resulting from the association of an H-2K (or H-2D) class I product with a viral antigen (e. g., a virus/H-2K complex). In a control experiment, target cells of both haplotypes were treated with Antibodies directed against the budding virus, an effect that is not haplotype-restricted. As a result, antiviral antibodies and Complement lyse infected target cells regardless of haplotype.

The advantage of such a dual recognition system for foreign antigens is that free virus (not associated with MHC molecules) cannot completely block all specific Tc receptors. More importantly, MHC restriction enables T cells to distinguish between endogenous and exogenous antigens.

Helper T cells (Th) operate on similar principles of MHC-restricted recognition. They recognize antigens, for instance on macrophages and B cells, in association with MHC class II molecules, which serve to transmit recognition signals between antigen-presenting cells (specifically macrophages) and Th cells.



Last update: 13/08/2026

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