Three different strain combinations have produced alloantisera that agglutinate red cells from mouse strains C57BL/6J and C57BL/By, but do not react with cells from strains C57BL/10Sn, C57BL/10J, or C57BL/10Gn-Rn/+ (Rn/+ or +/+). Erythrocytes from 35 H-2 and non-H-2 congenic lines on the C57BL/Sn background are unreactive, whereas red cells from all other inbred strains tested to date, including related strains C57L/J, C57BR/cdJ, C57BL/KsJ, and C58/J are reactive. This pattern of serological reactivity is different from that of any known erythrocyte antigen system of the mouse and suggests residual heterozygosity or a mutation in an early progenitor of the C57BL/10 substrain family.
We have recently developed a congenic line in which a histocompatibility (H) allele from strain C57BL/10Sn was introduced onto a C57BL/6J background by 16 successive generations of backcross followed by sib mating. Cells from mice selected at the first intercross generation for homozygosity at the introduced H allele were serotyped with one of the alloantisera characterized above. They were unreactive or phenotypically like cells from strain C57BL/10Sn. Thus it appears that the erythrocyte antigen described here is determined by a locus closely linked to, or perhaps identical with, a histocompatibility locus that distinguishes between strains C57BL/6J and C57BL/10Sn.