Effects of housing on the thymic deficiency in dwarf mice and its reversal by growth hormone administration.

Initial studies on T cell development in the Snell Dwarf (dw/dw) strain of mice, which are deficient in the production of anterior pituitary hormones, have been interpreted to indicate a clear dependence of T cell development on endocrine system-derived factors. However, normal thymopoiesis in this strain has also been reported. The aim of the present study was to reconcile these contradictory data in order to define the role of anterior pituitary hormones in the thymus. The results indicated that if female dw/dw mice are housed together with their normal-sized littermates, thymic cellularity and the frequency of CD4(+)CD8(+) thymocytes are markedly reduced. However, administration of growth hormone could reverse these decreases seen in the double-positive T progenitor cells. Taken together, the data indicate that stress is the unifying parameter that can explain the disparate dw/dw mouse literature and suggest that endocrine effects on the T cell development can best be understood by interpreting the literature in this context.