Differential effects of growth hormone and prolactin on murine T cell development and function

DW/J dwarf mice have a defect in their anterior pituitary and are deficient in growth hormone (GH) and prolactin (PRL). These mice have been demonstrated previously to have a deficiency in CD4/CD8 double-positive thymocytes, which could be corrected by treatment of these mice with recombinant human GH. Since PRL has been implicated in T cell function and human GH can interact with the PRL receptor, DW/J dwarf mice were treated with either ovine GH (ovGH) (20 micrograms/d) or ovine PRL (ovPRL) (20 micrograms/d). The ovine hormones can only bind their own specific receptors in the mouse. After several weeks of treatment, it was found that these two hormones produced markedly contrasting effects on T cells. Phenotypic analysis of the lymphoid organs was performed by flow cytometry and the functional capability of the peripheral T cells was assessed by immunizing the mice and determining the extent of antigen-specific proliferation of T cells obtained from the draining lymph nodes or by determining splenic mitogen responses. The results indicated that ovGH administration to dwarf mice resulted in significant increases in thymic cellularity yet had little effect on peripheral T cell responses. In contrast, the administration of ovPRL resulted in a further decrease in thymic cellularity when compared with untreated dwarf mice. No thymic effects of either ovGH or ovPRL administration were detected on the normal +/? counterparts. However, ovPRL administration resulted in a significant increase in the number and function of antigen-specific peripheral T cells in both immunized dwarf and +/? mice. The adjuvant effects of PRL occurred even though the mice also received complete Freund's adjuvant. These results suggest that neuroendocrine hormones may act in concert in T cell development. GH appears to promote thymocyte proliferation, while PRL appears to decrease thymus size and yet augment the number and function of antigen-specific T cells in the periphery.