Evidence that strong Mls determinants are nonpolymorphic.

Gene products of the murine Mls locus elicit high primary mixed lymphocyte reactions (MLRs). Although this locus is considered to have four alleles, only two of these alleles, i.e., Mlsa and Mlsd, give strong responses in primary MLRs. This paper presents a series of experiments to show that Mlsa and Mlsd are in fact antigenically indistinguishable. Strong Mls determinants thus appear to be nonpolymorphic.