Effects of gonadal steroids and their antagonists on the humoral immune response of immune-selected broiler chicks.

The effects of gonadal hormones, testosterone (Te) and estrogen (E2) as factors in the development of the immune system in two lines, high response (HC) and low response (LC), of broiler chickens divergently selected for early or late immune maturation were studied. For this purpose, plasma Te and E2 levels were tested and correlated with immune response. Also, the effects of exogenous administration of gonadal steroids testosterone propionate (TP), dihydrotestosterone (DHT), and estradiol 3-benzoate (EB), and the nonsteroidal androgen antagonist flutomide (Flu) and anti-estrogen tamoxifen (Tam) on the immune system were studied. Male chicks of the LC line had a higher level of endogenous Te during first 30 d posthatch. The administration of TP or DHT had no noticeable effect on the humoral immune response, whereas DHT suppressed growth of the bursa of Fabricius of both sexes of HC line. No differences in the endogenous E2 level were observed between sexes in either line. Administration of EB inhibited comb and testicle growth and enhanced significantly the humoral immune response to Escherichia coli and sheep erythrocytes (SRBC). The anti-androgen Flu and anti-estrogen Tam strongly inhibited humoral immune response to E. coli and SRBC antigen, whereas no effects on comb and testicle growth were observed. The experimental results suggest that gonadal hormones have similar principal posthatch effects in avian as in mammals; however, the gonadal steroids prehatch effects and the genetic-physiological-environmental effects require further study.