Mlsa determinants: relationship to Fc gamma receptor and tissue distribution.
We have analysed the genetic relationship between Mlsa and Fc gamma R in mice. Using the Fc gamma R-specific DNA probes, we were unable to detect a restriction fragment length polymorphism (RFLP) which is consistent in DNA derived from Mlsa strains and which differed from that of Mlsb strains, while we could see a polymorphism that distinguishes Ly17.1 from Ly17.2, alleles of the Fc gamma R. These results strongly suggest that Mlsa is neither a product of the alpha Fc gamma R nor of the beta Fc gamma R gene. Furthermore, we have re-examined the tissue distribution of Mlsa determinants using a major histocompatibility complex (MHC) class II antigen-positive T-cell tumour as well as a pure population of bone marrow derived macrophages of Mlsa genotype. Both these cell types were recognized to varying degrees by alloreactive cells; however, none of them expressed functionally detectable Mlsa determinants. We conclude from our studies that Mlsa is a highly stimulatory self peptide that is exclusively expressed in B cells.