A,B, Statistical analysis of serum IgM and IgG levels in unmanipulated mice. Data from 10 WT, 6 b12HL, 10 b12H and 4 b12L mice. C, Env (JRFL)-specific IgM and IgG concentrations from 6 b12HL and 6 b12H mice. b12 IgM or IgG1 was used to standardize the assay. D, Analysis of neutralization activity against JRFL pseudovirus of normal sera from 4 b12HL and 4 b12H mice. Shown are mean values and SEM. Results were derived from at least three independent experiments except for the serum analyses which were obtained in one experiment.