How do immune response genes work?

Ir genes could operate either by controlling T-cell receptor repertoires, or by controlling antigen presentation to T cells. The idea thatIr genes are a germline set ofV genes for T-cell receptors for foreign antigens can be excluded. Models involving indirect control of the T-cell receptor repertoire during somatic generation of diversity are still possible, though evidence fromH-2 mutations suggests that the probability of their being correct is low. The idea thatIr genes control cell-surfaceMHC antigens that must associate closely with foreign antigens in the surface of antigen-presenting cells to cause T-cell activation is compatible with most, if not all of the available data.