Polymeric IgA antibody response to rabbit antithymocyte globulin in renal transplant recipients

Treatment of transplant recipients with heterologous antithymocyte globulin (ATG) can induce the production of antibodies to the ATG itself. Such responses have, however, not been fully defined in terms of the kinetics, class, and quantities of antibodies produced. We have studied these parameters in 32 renal transplant recipients who had received rabbit ATG as treatment for acute rejection episodes. Antibodies to rabbit IgG were detected in the sera of all patients; employing an enzyme- linked immunosorbent assay (ELISA), the majority of patients were shown to produce specific antibodies of the IgG, IgA, and IgM class. Anti-ATG antibodies were first detected 6—48 days after the initial injection of ATG and usually attained peak values within 23 days. The IgM and IgA responses decreased within 1—2 months, whereas the IgG response remained elevated for 2—12 months. Gel filtration studies indicated that the IgA and IgM antibodies directed to the rabbit ATG were polymeric. Furthermore, the polymeric IgA bound secretory component, indicating the presence of J chain. In 6 patients, circulating immune complexes that contained rabbit IgG were detected. The clinical symptoms and laboratory findings did not correlate with the production or quantities of the different classes of antibodies. Possible explanations for the prominent IgA response to intravenous injections of ATG are discussed.