Protective immunity to Nippostrongylus brasiliensis in the rat. Central role of the lymphocyte in worm expulsion.

Evidence is presented to show that the expulsion of adult Nippostrongylus brasiliensis worms from the intestine of the rat requires the presence of functional lymphocytes. It has been established by previous workers that expulsion involves two steps, the first involving antibody action on the worms, and the present work shows that the second step requires the participation of lymphocytes. This conclusion comes from experiments in which the expulsion of worms already affected by step 1 (damaged worms) was examined in rats which were depleted of or restored with lymphocytes, as follows: Expulsion of worms was inhibited in young rats and in irradiated adult rats (confirming previous work) and inhibited in adult, neonatally thymectomized rats treated with antithymocyte antiserum. The expulsion mechanism was restored in irradiated adult rats and in young rats by giving them syngeneic mesenteric lymph node cells from uninfected adult donors. Macrophage enriched peritoneal exudate cells did not restore the expulsion mechanism either in young or in irradiated adult recipients. Mesenteric lymph node cells subjected to 5000 r prior to injection of the recipients also failed to restore the expulsion mechanism in adult rats.