Growth hormone restores glucocorticoid‐induced T cell suppression

Growth hormone (GH) is a potent anabolic hormone, and its clinical use has been extended to the improvement of metabolic imbalance in many disease,s including autoimmune disorders treated with glucocorticoids (GCs). GH has, however, a potential action on the immune system, and this might be a demerit in GH therapy for those diseases. We report here the anti‐GC effects of GH on T lymphocytes. Human peripheral T lymphocytes (HPTLs) expressed GH receptor mRNA. GH stimulated tyrosine phosphorylation of cellular proteins, including JAK2 and STAT5b in HPTLs. GH and IGF‐I alleviated dexamethasone (Dex)‐induced suppression of [ 3 H]thymidine incorporation into HPTLs. GH alleviated Dex‐induced apoptosis in CD4 + (positive) HPTLs. GH increased Bcl‐2 expression in CD4 + HPTLs but not in CD8 + HPTLs. In vivo, GH raised the CD4/8 ratio of T lymphocytes in rats chronically administered with Dex. These findings indicate that GH may inhibit GC‐induced apoptosis predominantly in CD4 + T lymphocytes and present important implications of GH therapy, especially for autoimmune disorders treated with GCs.