Immunogenetics of a thymus antigen in lymphoma-prone and lymphoma-resistant colonies of wild mice.

The Thy-1 (theta) antigen was identified in wild mice (Mus musculus), the frequency of its alleles was determined in two natural populations of wild mice, and the possible T-cell origin of spontaneous lymphomas was investigated in one of these populations. Reaction patterns for Thy-1 antigen with the use of direct cytoxicity and indirect absorption assays were identical in wild mice and inbred strains. Between 15 and 55 percent of viable spleen cells from healthy young or old wild mice were Thy-1 positive. Spleen, but not brain, cells from older wild mice were less strongly positive. Wild mice from the lymphoma-prone population were polymorphic for Thy-1alpha and Thy-1beta alleles, whereas wild mice from the lymphoma-resistant populations were homozygous for the Thy-1beta allele. Contrary to expectation, a higher frequency of the Thy-1beta allele was noted in the mice with lymphomas. Alleles at two other loci on chromosome number 9 (Mod-1alpha and Trfbeta) were fixed in both populations. The absence of detectable Thy-1 antigen on spleen cells (despite its detectability in undiminished titer in brain tissue) in 80 percent of mice with lymphomas, along with the absence of thymus involvement in the lymphomatous proliferations, suggested that these tumors are derived from an expansion of non-thymus-derived cells.