Protection of nude rats against Toxoplasma infection by excreted-secreted antigen-specific helper T cells.

In the present work we demonstrate the implication of excreted-secreted antigens in eliciting the protective cell-mediated immunity developed by rats toward Toxoplasma gondii. We first showed that 10(4) specific T cells from T. gondii-infected rats conferred to nude rats the ability to resist an infection by the highly virulent RH strain of T. gondii. In a second series of experiments, the role of excreted-secreted antigens in this protection was demonstrated. After the adoptive transfer to nude rats of various doses (10(3), 10(4), 10(5)) of excreted-secreted antigen-specific helper T cells (propagated in vitro during one month), significant protection toward T. gondii was induced. Moreover, these cells were responsible for a specific antibody response in nude rats, which are normally unable to develop any specific humoral response. The specificity of these antibodies was directed toward different molecules with molecular masses of 104, 97, 57, 39, 30, 21, and 18 kilodaltons; some of these have been previously characterized as major excreted-secreted antigens.