Corticosteroid action on lymphocyte subpopulations and humoral immune response of axolotl (urodele amphibian).

The effect of in vivo hydrocortisone (HC) treatment on thymocytes, splenic and blood lymphocytes and on allogeneic and humoral immune responses were investigated in the axolotl (urodele amphibian). HC induces a profound lymphocytopenia in the thymus (83% HC sensitive) and the spleen (50% HC sensitive) but not in the blood. The density gradient analysis of HC-treated axolotls showed that thymic cell populations of light density were more sensitive than populations of high density. The timing of HC administration in relation to the antigenic challenge is crucial for the humoral immune response. If HC injection is given 8 days before or on the same day as injection of horse red blood cells (HRBC), the antibody response is markedly enhanced. If HC injection occurs 8 days after injection of HRBC or on the day of the maximum anti-HRBC response, the antibody response is unchanged. The allograft immune response is not affected by HC treatment. The parallelism of the enhanced anti-HRBC response after HC treatment, with the same enhanced response obtained in adult thymectomized (ATx) animals, as well as in ATx-HC-treated axolotl, may be explained by the presence of a corticosensitive, T-like population of suppressor cells in axolotl.