Biochemical characterization of murine lymphoid alloantigen Ly-m20.2, a cell surface marker controlled by a gene linked to the Mls locus.

The lymphoid alloantigen Ly-m20.2 is expressed on the majority of B cells and a wide variety of hemopoietic cells including stem cells. However, it is not detectable on T lymphocytes. Genetic studies indicate that expression of Ly-m20.2 is controlled by a gene(s) closely linked to the M1s locus. Our present biochemical analysis shows that Ly-m20.2 is a monomeric glycoprotein of 55,000 to 60,000 daltons, with no detectable intramolecular disulfide bonds. The Ly-m20.2 molecules of tissues and clonal cell lines exhibit size and charge heterogeneity that can be eliminated by the complete removal of N-linked sugars with the enzyme endo-F or by inhibiting glycosylation with tunicamycin. The resulting unglycosylated Ly-m20.2 molecule migrates as a single band of 40,000 daltons in SDS-gels and behaves as a single charge species in IEF. The Ly-m20.2 antigen was compared biochemically with two other alloantigens: LyM-1, an alloantigen whose expression is also controlled by gene(s) tightly linked to the M1s locus, and Ly-17.1, an alloantigen serologically allelic to the Ly-m20.2 antigen. Immunoprecipitates obtained with the respective LyM-1 and Ly-17.1 antisera yielded similar 55,000 to 60,000 dalton molecules from cells of the appropriate mouse strains. In the case of LyM-1, sequential immunoprecipitation provided evidence that Ly-m20.2 and LyM-1 are identical.