In vivo lymphocyte responses in the draining lymph nodes of mice exposed to Schistosoma mansoni: preferential proliferation of T cells is central to the induction of protective immunity.

The in vivo cellular responses associated with the induction of specific immunity by attenuated larvae of Schistosoma mansoni in mice have been investigated. Using in vivo 5-bromo-2'-deoxyuridine incorporation, the changes in cell proliferation in the skin- and lung-draining lymph nodes (LN) of vaccinated animals were measured. A marked increase in the number of dividing cells was detected in both groups of LN, with a preferential increase in the proportion of proliferating T, relative to B, lymphocytes. Several dynamic components of cell migration have been examined to assess their relative contribution to the overall changes in the LN of immunized mice. It was determined that a significant part of the observed accumulation of cells is due to the effect of hyperaemia. There was no alteration in the affinity of the LN for T and B lymphocytes, but we concluded that the majority of recruited B cells failed to exit the nodes. The results have highlighted the importance of T cell proliferation within the draining LN for the successful immunization of mice with attenuated parasites.