In situ pulmonary responses of T cell and macrophage subpopulations to a challenge infection in mice vaccinated with irradiated cercariae of Schistosoma mansoni.

Cellular events related to the resistance induced by radiation-attenuated cercariae of Schistosoma mansoni were determined immunocytochemically in the lung tissues of mice. Thy-1, CD4, CD8, Mac-1 MOMA-1, MOMA-2, and Ia antigens were identified on cryostat sections by the immunogold-silver staining technique with specific monoclonal antibodies. In mice vaccinated with irradiated cercariae and challenged with normal cercariae, the number of Thy-1+ and CD4+ lymphocytes was increased dramatically relative to the normal numbers both in perivascular tissues and in focal cellular aggregates in the parenchyma of the lungs. A high ratio of CD4+/CD8+ T cells was noted in the aggregates, both in perivascular tissues and in the foci. Macrophages showing positive reactions for Mac-1, MOMA-1, MOMA-2, and Ia also infiltrated the foci. In control mice that were unvaccinated and challenged, foci showing positive reactions for the lymphocyte subpopulations barely were detectable in the lungs by day 14. The numbers of Thy-1+, CD4+, and CD8+ cells and the CD4+/CD8+ ratio in controls were considerably less than those in vaccinated/challenged mice over the period of observation. In conclusion, pulmonary cellular aggregates in vaccinated and challenged mice were composed mainly of Thy-1+ and CD4+ cell populations characteristic of delayed-type hypersensitivity (DTH) reactions. Thus, Thy-1+ and CD4+ cells in the lungs of vaccinated mice may be involved in the elimination of challenge parasites through DTH reactions.