EFFECT OF ALTERNATE-DAY HYDROCORTISONE THERAPY ON THE IMMUNOLOGICALLYIMMATURE RAT .2. CHANGES IN T-CELL AND B-CELL AREAS IN SPLEEN

The histologic effect of 400 mg/M(2)/day of hydrocortisone, given alte rnatively from day 7 to day 19 after birth, was studied on the spleen of the immunologically immature rat. Two days after the cessation of t reatment, the periarteriolar lymphatic sheaths were found to be largel y depleted of small lymphocytes. Immunoperoxidase studies confirmed a depletion of T lymphocytes. The effects of hydrocortisone on the thymu s seem to be more important than its direct lymphocytolytic effect in producing this splenic lesion. In contrast, no apparent change in the number of medium-sized B lymphocytes in the marginal zone was detected . Medium-sized B lymphocytes of the spleen, reported to be responsible for IgM synthesis, appeared to be subjected to a different mechanism of hydrocortisone action, other than lysis, resulting in a decrease in antibody production. Primary follicles were not seen in spleens of hy drocortisone-treated rats. Twenty-three days after treatment, spleens had a histologically normal appearance.