The humoral immune response to streptococcal cell wall-induced arthritis in the rat.

Abstract

I investigated the humoral immune response to streptococcal cell walls (SCW) in arthritis susceptible Lewis and resistant Fisher rats. All rats were given a single intraperitoneal injection of either SCW or saline (controls). Rats were sacrificed, three rats per time point, over an eleven week period and serum was collected for ELISA. SCW injected Lewis rats produced anti-SCW antibody, whereas control rats did not. Anti-SCW antibody was significantly elevated over controls between days 14-28 (post injection). Both saline and SCW injected Fisher rats produced anti-SCW antibody, but with different kinetics. Anti-SCW antibody increased by day 7 and remained elevated over controls till day 21, after which there was no difference. ELISA were designed to determine the SCW epitope(s) recognized by anti-SCW antibody. Formamide extracts of SCW, peptidoglycan and polysaccharide, were investigated along with the terminal epitope of polysaccharide, N-acetyl-D-glucosamine, and the peptidoglycan precursor peptide. The data revealed that anti-SCW antibody was directed against a combined SCW epitope, given the lack of significant binding to any of the SCW epitopes tested. Isotype analysis of anti-SCW antibody revealed that the Lewis response was composed primarily of IgG2a whereas the Fisher response was composed primarily of IgM. Binding of rat IgG isotypes to whole streptococcus, SCW, peptidoglycan, and polysaccharide was investigated, given the possibility of background binding by the streptococcal Fc-receptor. Streptococcal binding of rat IgG was specific for IgG2c and the polysaccharide portion of SCW was necessary for binding. Passive immunization of naive Lewis rats with antibody from rats with active arthritis was ineffective at transferring the disease. However, subcutaneous injection of affinity purified anti-SCW antibody or IgG into Lewis rats, followed twenty-four hours later by a single intraperitoneal injection of SCW, suppressed the acute phase and inhibited the chronic disease. IgM rheumatoid factor (RF) was present in the serum of both saline and SCW injected Lewis and Fisher rats. However, SCW injection only induced a significant increase in IgM RF (between days 3-7) in Lewis rats. Passive immunization of Fisher rats with affinity purified IgM RF (from Lewis serum), three days post SCW injection, was ineffective at inducing arthritis.