Investigation with dexamethasone of the processes which moderate immunity against the nematode, Haemonchus contortus,...

Treatment of sheep with the corticosteroid, dexamethasone, was used to investigate some properties of the immunoregulatory process which dampens the expression of protective responses against the abomasal nematode, Haemonchus contortus, and which may occur as an adaptation for evasion of host immunity by this parasite. The protective responses released by giving dexamethasone early in infection operated during a series of superimposed infections. Accordingly, they may also operate during field exposure to the parasite. Dexamethasone-released protective responses acted earlier than 7 days after infection. Accordingly, there is no reason to suggest that they are distinct from the responses which usually produce refractoriness to infection. Results from two consecutive but not superimposed infections show that activity of the immunoregulatory process identified by dexamethasone treatment can persist for a month. This implies that there is memory for immunoregulation in infection by H. contortus.