Serum levels of antibodies specific for CII. Comparison of isotype anti-CII IgG responses in thymectomized (Tx) and sham-operated (Sham) mice as measured in sera 35 days after immunization in MMC transgenic mice and the nontransgenic littermates. Open symbols represent IgG2a and filled symbols IgG1. The transgenic mice have significantly lower isotype levels compared with their nontransgenic littermates, but thymectomy had no effect. The same pattern was seen in female (A) and male (B) mice.