Monoclonal antibody identifies a new Ia-like (p29,34) polymorphic system linked to the HLA-D/DR region.

The Ia antigens of the mouse are the basis for the genetic control of the immune response. The HLA-D/DR locus is considered to be the human counterpart of the Ia subregion of the murine major histocompatibility complex. The HLA-D/DR antigens are polymorphic, and eight well defined alleles have been identified using alloantisera. More recently, 'supertypic' antigens (MB and MT) have been defined which identify clusters of HLA-D/DR specificities. Little is known about the molecular basis for the cellular and serological polymorphism of the HLA-D/DR antigens, as alloantisera are usually of very low titre and heteroantisera frequently lack monospecificity. We present here the preparation and characterization of a monoclonal antibody which defines a new polymorphic system of the HLA-D/DR region. This and similar antisera should now begin to provide the reagents with which to correlate molecular structure with the functional repertoire of the human Ia-like antigens.