Immunological aspects associated with suppression of hormone levels in rats infected with plerocercoids of Spirometra mansonoides (Cestoda).

The effect of the plerocercoid larvae of Spirometra mansonoides on hormone levels and the immune system of intact and hypophysectomized (Hx) rats was studied. Intact rats exhibited a decrease in serum growth hormone (GH) and thyroxine (T4) concentrations and a suppression of the humoral immune response 2 wk postinfection. At 4 and 9 wk postinfection, hormone concentrations and the humoral immune response returned to normal levels in the rats. When rats were infected with plerocercoids and then received daily injections for 2 wk of either GH or T4, the immune response returned to normal in the T4-injected, but not the GH-injected animals. Plerocercoid infection had no effect on the humoral immune response of Hx rats. The results of the present study suggest that PGF may act via an endocrine pathway to suppress the host's immune response enabling the parasite's survival in this host.