RECOVERY FROM FRIEND DISEASE IN MICE WITH REDUCED MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I EXPRESSION

Mice homozygous for the b allele of the MHC gene, H-2D, have a high in cidence of recovery from Friend virus infections, while mice heterozyg ous for the b allele at H-2D have a very low incidence of recovery. Pr evious experiments indicated that the low recovery rates associated wi th heterozygosity at H-2D might be related to a gene dosage effect req uiring the expression of two H-2D(b) alleles for high recovery. We inv estigated the effects of reduced H-2D(b) expression on recovery from F riend disease by using H-2(b) homozygous mice carrying a single beta(2 )-microglobulin gene disruption. These mice had reductions in cell sur face H-2D(b) expression comparable to those of H-2D(a/b) heterozygotes . Numerous cell types with various levels of H-2D(b) expression were e xamined, and in each case, the expression levels in the beta(2)-microg lobulin mutants closely reflected those observed in the H-2D(a/b) hete rozygotes. We found, however, that reduced expression did not affect r ecovery from Friend disease, indicating that heterozygous levels of H- 2D(b) expression are sufficient for the high-recovery phenotype previo usly associated only with H-2D(b) homozygotes.