An analysis of monoclonal T cell and antibody recognition sites on Ia molecules.

The advances made in understanding T cell and antibody recognition sites on Ia using monoclonal helper and alloreactive T cells are summarized. For many antibodies it has been possible to determine whether the antibody recognition site was determined by the alpha or beta chain. Such defined antibody reagents have allowed the definition of multiple functional antigen presenting sites on a given Ia molecule. Mutant antigen-presenting cells independently suggest the existence of such multiple functional sites. A detailed analysis of the I-Ab mutant bm 12 directly defines the chemical nature of one such site and suggests that it arose as a result of gene conversion. Such regions of Ia molecules may be important for both T-cell function and antibody-binding.