ALTERATIONS IN THYMIC AND BONE-MARROW LYMPHOCYTE SUBPOPULATIONS IN GNRH AGONIST TREATED PREPUBERTAL FEMALE MICE

Complex endocrine relationships exist among the hypothalamus, pituitar y, ovaries and thymus. There is also considerable evidence showing gon adotropin releasing hormone (GnRH) involvement in modulating immune sy stem functions. The present study investigated the sequential changes in functional lymphocyte subsets in primary lymphoid tissues of prepub ertal female mice in vivo following GnRH agonist treatment in slow rel ease microcapsule formulation. A direct two color immunofluorescence s taining followed by flow cytometry was employed. Single i.m injection of agonist significantly decreased both absolute and relative thymic w eights and absolute thymocyte counts. No differences, however, were ob served in the percentage of thymocytes expressing Thy 1.2, CD4 and CD8 . Absolute levels of thymic T cells, CD8 positive cells, immature cell s expressing both CD4 and CD8, and immature subsets differentiating to ward CD4 were significantly reduced two weeks after agonist treatment. The percentage of bone marrow B cells was also significantly decrease d at the second and third weeks following agonist administration. Func tional studies to determine in vivo cell-mediated immune function also indicated a significant suppression following agonist administration. These data, together with our earlier observatiors on secondary lymph oid tissues, suggest a general suppression of lymphocyte maturation at an early stem cell stage of development in prepubertal female mice in vivo.