EFFECT OF HYPOPHYSECTOMY AND GROWTH-HORMONE ON IMMUNE DEVELOPMENT IN THE DOMESTIC-FOWL

The effect of hypophysectomy and recombinant growth hormone (rcGH) tre atment on the growth and development of the immune system was investig ated in young chickens. Flow cytometric analysis of cell surface marke rs revealed no changes in the proportion of thymocytes expressing CT-1 a, CD4, and/or CD8 among any of the treatment groups. In contrast, the proportion of both single positive CD4 and CD8 peripheral blood lymph ocytes (PBL) was altered in hypox birds treated with rcGH compared to the vehicle-treated group. Specific-ally, rcGH treatment produced a de crease in the proportion of CD8+ cells and an increase in the percenta ge of CD4+ PBL. There was little change in the labeling intensity of P BL or thymocytes associated with any treatment; however, double positi ve (CD4+CD8+) thymocytes from hypophysectomized chicks that were not g iven rcGH had increased fluorescence relative to rcGH supplemented hyp ox chicks. As expected, hypophysectomy reduced body, skeletal, and thy mic growth. Treatment of hypox chicks with rcGH enhanced body weight w hile thymic weights were somewhat increased. Skeletal growth was not s ignificantly altered by rcGH. Bursal growth appeared refractory to eit her treatment. These studies support the conclusion that growth hormon e influences thymic growth and the maturation of thymus-derived lympho cytes. These results also demonstrate a biological activity for chicke n growth hormone derived through recombinant technology.