8-Mercaptoguanosine-mediated enhancement of in vivo IgG1, IgG2 and IgG3 antibody responses to polysaccharide antigens in normal and xid mice

We have examined the effects of the immune adjuvant 8-mercaptoguanosine (8sGuo) on the in vivo antibody response to the T-cell-independent type 2 antigen, TNP-Ficoll. While 8sGuo enhanced the IgG1, IgG2 and IgG3 antibody responses, it was without effect on the IgM antibody responses. Increasing the dose of injected 8sGuo from 30 to 300 mg or the frequency or its injection led to greater enhancement in the antibody response, which varied from 20 to 100 times that of control responses. The effect of 8sGuo was relatively early acting in that it no longer enhanced anti-TNP antibody responses when given 3 days after antigen injection. Its ability to mediate an adjuvant effect on antibody responses was demonstrable even under conditions where the injected antigen by itself stimulated either no or low-level antibody responses. Thus, it enhanced the antibody response to the very weak antigen, pneumococcal polysaccharide, and restored the antibody response of nonresponder immune defective xid mice to TNP-Ficoll. These results extend the earlier observations of Goodman and coworkers by demonstrating that in vivo IgG response to type 2 polysaccharide antigens can be enhanced in normal mice and restored in xid immune-deficient mice.