Correlation Between Levels of Immunoglobulins and Immune Complexes in Plasma of C57BL/6 and C57L/J Mice Infected with MAIDS Retrovirus

Infection with helper-free, defective MAIDS murine leukemia virus (MuLV) caused a rapid polyclonal activation of B cells in 0.75-, 2-, and 6-month-old C57L/J mice (H-2^b, Fv-1^n/n), similar to that in C57BL/6 mice (H-2^b, Fv-1^b/b), which was recognized by elevated plasma immunoglobulin concentrations. However, changes in plasma immunoglobulin levels differed in C57L/J and C57BL/6 mice. In C57L/J mice, infection resulted in a rapid increase in plasma IgM and IgG_2a, and the elevation of IgG_2a persisted undiminished for 21 weeks. Levels of IgG2b also became slightly elevated, but those of IgG, and IgG₃ were not significantly affected. Plasma of 6 to 7-month-old C57BL/6 mice contained already high levels of IgM (30–40 mg/ml), which persisted undiminished in uninfected mice but decreased progressively in infected mice to 10% of the original concentration during 25 weeks of observation. In C57BL/6 mice, plasma IgG₁ and IgG_2b as well as IgG_2a became similarly elevated after infection but also only transiently. Their levels began to decrease progressively about 10 weeks after infection and fell to far below the maximum concentration observed. The drastic loss of plasma IgM and IgGs observed in C57BL/6 mice during the later stages of MAIDS MuLV infection did not seem to be a consequence of the polyclonal activation of B cells per se but seemed to reflect additional immunological abnormalities arising in infected C57BL/6 but not C57L/J mice. In both mouse strains these changes in plasma Ig levels correlated with the formation of Ig-containing immune complexes that bound to high-affinity, protein-binding ELISA plates in the absence of antigen coating, which may represent unusual forms of self-antigen-antibody complexes.