Further evidence implicating murine leukemia-like virus in the disorders of NZB mice was afforded by a study of antigens associated with murine leukemia virus (MuLV). MuLV group antigens were prevalent in extracts of spleen, kidney, and, to a lesser extent, thymus throughout a substantial portion of the life span of NZB mice as well as in extracts of lymphomas and sarcomas indigenous to the strain.

G (Gross) soluble antigen, type-specific antigen, was first detected in plasma of untreated NZB mice at 3 months of age. G soluble antigen production increased thereafter in line with age, with 50% of reactions becoming positive at 5.3 months and 100% at 7 to 9 months.

From months 3 to 9, the time-response curve for positive conversion of direct antiglobulin (Coombs) tests in untreated NZB mice corresponded closely to that for G soluble antigen production.

Beyond the 9th month, G soluble antigen underwent elimination from the plasma of NZB mice, with positive reactions reduced to 50% at 13.3 months and to 0% at 18 months. G natural antibody was first detected in the serum of NZB mice at about 10 months of age and increased thereafter in line with age. The curves for G antibody production and G soluble antigen elimination bore a reciprocal relation to each other with crossover at 50% response occurring at 13.3 months.

Significant proteinuria, a functional manifestation of membranous glomerulonephritis, became increasingly prevalent in female NZB mice as G soluble antigen was eliminated from plasma. Cumulative mortality of female NZB mice, mainly attributable to renal glomerular disease, increased in phase with G antibody production. MuLV group antigens were identified in the glomerular lesions by the immunofluorescence method.

Positive conversion of direct antiglobulin tests was significantly delayed by vaccinating baby NZB mice with formaldehyde-inactivated cell-free filtrates of older NZB mouse spleens. The plasmas of vaccinated NZB mice with negative direct antiglobulin reactions at 4 to 7 months were likewise negative when tested for G soluble antigen. The 50% response time for G antibody production in the vaccinated NZB mice occurred at 7.3 months, that is, 6 months earlier than in untreated NZB mice.

The collective findings implicate murine leukemia-like virus in the etiology of autoimmune hemolytic disease and membranous glomerulonephritis, as well as malignant lymphoma, of NZB mice and suggest that virus-specified cell-surface and soluble antigen is a factor in the immunopathogenesis of the renal disease and possibly also the autoimmune hemolytic disease.

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