Thymic Control of Secretory Antibody Responses in the Rat

The effect of neonatal thymectomy on salivary and serum antibody responses was studied in rats. Local immunization of thymectomized rats with a T-dependent antigen (DNPBGG) elicited negligible amounts of IgA anti-DNP antibody in saliva. In contrast, both normal and sham-thymectomized animals demonstrated substantial levels of salivary IgA antibody. All thymectomized rats locally injected with a T-independent antigen (DNP-Lys-Ficoll) exhibited salivary IgA antibody production. Salivary IgG antibodies were somewhat decreased in thymectomized rats injected with either antigen; however, the final effect of T cell deprivation on IgG synthesis was not as pronounced as on IgA synthesis. Serum IgA antibody was induced in control rats injected with DNPBGG, whereas this Ig class of antibody was absent in thymectomized rats. The results suggest that thymus-derived cells exert a regulatory influence on both serum and secretory IgA responses to antigens.