RECRUITMENT OF LYMPHOCYTES TO THE LUNG THROUGH VACCINATION ENHANCES THE IMMUNITY OF MICE EXPOSE TO IRRADIATED SCHISTOSOMES

The effector mechanism, which operates against challenge parasites in the lungs of C57BL/6 mice vaccinated once with irradiated cercariae of Schistosoma mansoni, is mediated by CD4(+) T helper lymphocytes. Howe ver, adoptive transfer of immunity from vaccinated donors to naive rec ipients by using sensitized T cells has not proved successful. One exp lanation may be that the recruitment of sensitized T lymphocytes to th e lungs by vaccinating parasites to arm that organ is not reproduced b y transfer protocols. We have used the technique of parabiosis, as a m eans of adoptive transfer, to demonstrate the relevance of pulmonary T cells to protection. Sensitized and naive partners were joined surgic ally for a 28-day period, coincident with priming of the immune system . A vascular union rapidly developed, and sensitized T cells were dete cted in the spleens of the naive partners. When parabionts were challe nged percutaneously 10 days after separation, the level of immunity tr ansferred to the naive partners was approximately two-thirds that of t heir vaccinated counterparts. The naive partners, unlike the vaccinate d animals, did not recruit lymphocytes to the lungs during the priming period. In contrast, after percutaneous challenge, schistosome-specif ic lymphocytes were recruited to the lungs of both separated parabiont s. The importance of lymphocytes recruited to the lungs during the pri mary response was revealed by an intravenous challenge with lung schis tosomula; this eliminates the opportunity for secondary immune respons es prior to parasite arrival in the lungs. In this situation, the vacc inated partners showed 47% immunity while the naive partners were not protected. We conclude that the presence of specific T cells in the lu ngs at the time of challenge confers a significant advantage, permitti ng a more effective recall response that in animals lacking such resid ent cells.