Thymic involution and recovery: immune responsiveness and immunoglobulins after neonatal prednisolone in rats.

Doses of 1.5 mg of prednisolone to newborn rats cause massive thymic involution and peripheral blood lymphocyte depletion without excessive mortality. By 3 weeks thymic mass, thymocytes and peripheral blood lymphocyte levels have all recovered fully, but antibody responsiveness to typhoid `H' antigen is still depressed. As late as 10 weeks diminished levels of a serum immunoglobulin provisionally identified as IgA and depressed `H' agglutinin titres are found in male but not in female treated rats.