CHANGES IN LYMPHOID-TISSUE AFTER TREATMENT WITH A GONADOTROPIN-RELEASING-HORMONE ANTAGONIST IN THE NEONATAL MARMOSET (CALLITHRIX-JACCHUS)

PROBLEM: The effect of neonatal treatment with a gonadotropin releasin g hormone (GnRH) antagonist on the morphology and distribution of lymp hocytes in lymphoid tissue of the infant marmoset was examined. METHOD OF STUDY: From a screened panel of antihuman antibodies for specific immune cells, antibodies for the CD20 and CD3 antigens showed excellen t reactivity with marmoset tissue. Five sets of marmoset twins were tr eated with either the GnRH antagonist or a vehicle from birth, and wer e euthanized at 7 to 9 (3 sets) or 16 to 20 weeks (2 sets) of age. The spleen, thymus, and inguinal lymph nodes from each animal were proces sed for immunocytochemistry, and the number of cells expressing the CD 20 and CD3 antigens were quantified. RESULTS: Control twins exhibited high plasma levels of testosterone, characteristic of the neonatal per iod, whereas testosterone concentrations were reduced (P = 0.001) to d etection limits in the GnRH antagonist-treated twins. Microscopic eval uation suggested that treatment reduced the volume and cellularity of the thymic cortex, resulting in a decrease in the cortical-to-medullar y ratio. Treatment reduced (P = 0.046) the number of thymocytes expres sing the B-cell antigen (CD20) and marginally lowered (P = 0.067) the number expressing the T-cell antigen (CD3) in the thymic medulla. In t he spleens of treated animals, periarterial lymphatic sheaths were les s prominent on microscopic examination, and there were marginally fewe r (P = 0.064) CD3+ cells. Numbers of CD20+ lymphocytes in the peripher al white pulp of the spleen and in the germinal centers of the lymph n odes, or CD3+ cells in the paracortex and germinal centers of the lymp h nodes, were not altered by treatment. CONCLUSION: Neonatal treatment with a GnRH antagonist may alter maturational processes for B and T c ells in the thymus and spleen of the marmoset and may deprive the immu ne system of its normal sensitivity to GnRH at a potentially critical time in development.