Human CD4+ and CD8+ T lymphocytes are both cytotoxic to Toxoplasma gondii-infected cells

Abstract

Studies to determine if Toxoplasma gondii-specific human T cells lyse parasite-infected cells have yielded conflicting results. Furthermore, attempts to obtain human cytotoxic CD8 ؉ T lymphocytes have been difficult because of the lack of a reproducible system for their generation. By using paraformaldehyde-fixed, T. gondii-infected peripheral blood mononuclear cells as antigen-presenting cells, we developed a method whereby T. gondii-specific T-cell lines can be reproducibly generated. Six T. gondii-specific T-cell lines were generated from an individual chronically infected with T. gondii. Cytofluorometric analysis of these lines revealed >99% CD3 ؉ , 85 to 95% CD3 ؉ ␣␤ T-cell-receptor-positive (TCR ؉), 5 to 9% CD3 ؉ ␥␦ TCR ؉ , 50 to 70% CD4 ؉ , and 20 to 40% CD8 ؉ cells when cells were examined during the first 3 weeks of stimulation and >99% CD3 ؉ , >99% CD3 ؉ ␣␤ TCR ؉ , <1% CD3 ؉ ␥␦ TCR ؉ , 20 to 40% CD4 ؉ , and 60 to 80% CD8 ؉ cells when cells were examined between 5 and 11 weeks. Both CD4 ؉ and CD8 ؉ T cells had remarkable cytotoxic activity against T. gondiiinfected target cells (30 to 50% specific Cr release at an effector-to-target ratio of 30:1) but not against uninfected target cells (<10% at an effector-to-target ratio of 30:1). Cytotoxic activity by the whole T-cell lines was not T. gondii strain specific. Whole T-cell lines were cytotoxic for target cells infected with the C56 and ME49 strains and the RH strain (which was used to infect peripheral blood mononuclear cells). T. gondiispecific T-cell lines displayed the predominant expression of V␤7 TCR. The CDR3 regions of the V␤7 TCRs of these T-cell lines showed a striking degree of sequence identity (oligoclonality). T-cell lines obtained by the method reported here can be used to characterize functional activity of T-lymphocyte subsets in humans infected with T. gondii.

CD4-mediated and CD8-mediated cytotoxic and proliferative immune responses to Toxoplasma gondii in seropositive humans

“…allowed for generation of CD8 ϩ T. gondii-specific CTL (29). In furtherance of those investigations, in the present work we showed that T. gondii-infected APC hampered PHA-induced cell proliferation and that fixed infected APC did not cause cell culture death, as did unfixed infected APC, suggesting the elaboration of a suppressive factor or factors.…”

“…LCL as APC were irradiated with 6,000 rad prior to use. Paraformaldehyde-fixed APC were produced exactly as for unfixed APC and then fixed according to the method of Montoya et al (29).…”

“…Paraformaldehyde fixation of infected APC altered some measures of immune responses. It was recently demonstrated that paraformaldehyde-fixed T. gondii-infected APC elicited human CD8 ϩ T. gondii-specific CTL (29). We thus assessed cellular proliferation in response to APC which had been fixed in this manner.…”

Difference in <i>Toxoplasma gondii</i> Seroprevalence Rates Due to Low and High CD4 Counts in Patients with HIV/AIDS

“…In HIV-infected population, the risk of toxoplasmosis increases depending on the immunosuppressive status of the patients. Sensitized CD4 + T lymphocytes are cytotoxic for T. gondii infected cells, and CD4 + T cells are unable to suppress the latent infection due to immuno-deficiency in HIV-infected patients (9). Although cerebral toxoplasmosis occurs most commonly in HIV-infected patients having CD4-counts below 100 cells/mm 3 ; rare cases are reported among patients having CD4-counts up to 200 cells/ mm 3 (6,10).…”

Complete Protection against LethalToxoplasma gondiiInfection in Mice Immunized with a Plasmid Encoding theSAG1Gene

“…To elicit protective immunity against an otherwise lethal dose of T. gondii, the appropriate cellular immune response has to be initiated, which could include both CD8 ϩ and CD4 ϩ T lymphocytes (18,23). This seems to occur after infection with the sublethal strain T. gondii ts-4, which provides protection against challenge with the lethal strain (7), and mice infected with the cyst-forming strain SSI119 are protected against challenge with the lethal RH isolate.…”