protein membrane-spanning 4-domains subfamily A member 1 A protein that is a translation product of the human MS4A1 gene or a 1:1 ortholog thereof. B-cell differentiation antigen Ly-44 B-cell surface antigen CD20 B-lymphocyte antigen CD20 B-lymphocyte surface antigen B1 Bp35 CD20 Ly-44 MS4A1 Ms4a2 leukocyte surface antigen Leu-16 lymphocyte antigen 44