Effect on parasite eradication of Pneumocystis carinii-specific antibodies produced in the presence or absence of CD4(+) alphabeta T lymphocytes.

The contribution of specific antibodies (Ab) to successful clearance of Pneumocystis carinii from host pulmonary tissues has received increasing attention. Sera collected from diseased recombinase-activating gene (RAG)-1(-/-), TCRbetaxdelta(-/-), TCRbeta(-/-) and Abeta(-/-) mutants as well as from aerogenic parasite-exposed (aero) and intranasally (i. n.) infected C57BL/6 mice were transferred to RAG-1(-/-) mutants inoculated with freshly isolated parasites. All sera, except for RAG-1(-/-) serum, contained P. carinii-specific Ab of varying isotype concentrations. Four weeks after serum treatment pulmonary parasite numbers were reduced slightly by Abeta(-/-) and C57BL/6-aero sera, and markedly by TCRbeta(-/-) and C57BL/6-i.n. sera. Our data reveal: (1) T cells are essential, and CD4(+) T cells are important for formation of protective Ab; (2) at least in the absence of alpha beta T cells, gamma delta T cells provide help for protective Ab. In vitro treatment of bronchoalveolar lavage cells with the different sera largely led to comparable results. Opsonizing Ab impeding parasite attachment to host cells, as well as Ab possibly neutralizing parasite-secreted products were implicated. Furthermore, serum components other than Abappear to participate in resistance to fungal manifestation.