The role of the recirculating thymus-dependent lymphocyte in resistance to Trichostrongylus colubriformis in the guinea-pig.

Abstract

The effect of removal of the thymic small lymphocyte on parasite immunity in the guinea-pig was studied. The source of these cells (the thymus) was surgically removed at birth and the reservoir (the recirculating pool) was depleted by long-term lymph drainage immediately before challenge infection when the animals were about 400 g body weight. This combined treatment caused the loss of resistance to the helminth parasite Trichostrongylus colubriformis. Usually the parasite is rejected by the immune mechanisms of the host between 30 and 35 days following infection in the guinea-pig. Removal of the thymic small lymphocytes resulted in survival for up to 100 days. No immuno-suppressive treatment was given during this period of prolonged survival of the parasite. Since the parasite survives for about 100 days in its natural host (the sheep) elimination at this time in the guinea-pig may be due to senescence rather than an immunological mechanism. The implications of these findings are discussed.