The influence of the lpr gene on B cell activation: differential antibody expression in lpr congenic mouse strains.

Spontaneous immunoglobulin production in four strains of lpr/lpr congenic mice was investigated to identify genetic interactions in lpr-induced polyclonal B cell activation. Sera were obtained from male and female lpr/lpr mice of the MRL, B6, C3H, and AKR strains as well as controls of +/+ genotypes. Antibody levels were compared at the time of peak response. Quantitative antibody determinations were performed by isotype-specific ELISA assays using responses to single-stranded DNA (sDNA), mouse IgG, rabbit IgG, and keyhole limpet hemocyanin as models. Among the strains studied there were significant differences in the antibody levels observed, with the strain producing highest levels dependent on the response measured. Thus, MRL-lpr/lpr produced the highest levels of IgG anti-sDNA while B6-lpr/lpr mice produced more anti-IgG than mice of other strains. Within each strain, the lpr gene appeared to affect the IgG more than the IgM response. A consistently high response by females was observed only in B6-lpr/lpr mice. These studies suggest that lpr-induced polyclonal B cell activation is influenced by the background genome with the extent of these genetic effects variable among responses.