Induction and suppression of lymphocyte proliferation by antigen extracts of Ostertagia ostertagi.

To obtain an insight into the responses of T-cells of cattle to Ostertagia ostertagi, the responses of peripheral blood and lymph node lymphocytes to O. ostertagi antigen extracts were determined in both exposed and naive calves. The lymphocyte responses induced by O. ostertagi antigen extracts of the third (L3) and fourth (L4) larval stages, as well as adult worms, were analysed. Although peripheral blood lymphocyte responses were very low or absent, abomasal lymph node lymphocytes of exposed animals showed a strong response to the L3 antigen extract. No such response was observed in naive calves or in mesenteric lymph node cells of exposed calves. L4 and adult worm antigen extracts suppressed the proliferative responses induced by the L3 antigen extract. Whether or not this suppressive effect plays a role in the slow rate at which protective immunity develops against O. ostertagi is under further investigation.