Simultaneous depletion of CD4+ and CD8+ T lymphocytes is required to reactivate chronic infection with Toxoplasma gondii.
C57BL/6 mice chronically infected with an avirulent strain (ME-49) of Toxoplasma gondii were used to study the mechanisms by which T lymphocytes and IFN-gamma prevent reactivation of latent infection. Infected animals were treated with mAb, either anti-CD8, anti-CD4, anti-CD4 plus anti-CD8, anti-IFN-gamma, or anti-CD4 plus anti-IFN-gamma and the mice followed for survival, histopathology, cyst numbers, and spleen cell cytokine responses. In agreement with previously published findings, treatment with anti-IFN-gamma antibodies fully reactivated the asymptomatic infection, inducing massive necrotic areas in the brain with the appearance of free tachyzoites and death of all animals within 2 wk. Mice treated with the combination of anti-CD4 plus anti-CD8 antibodies showed augmented pathology and mortality nearly identical to the anti-IFN-gamma- treated animals. In contrast, treatment with anti-CD4 or anti-CD8 mAb alone failed to result in significantly enhanced brain pathology or mortality. In additional experiments, full reactivation of infection was observed in mice treated with anti-CD4 plus anti-IFN-gamma indicating that CD4+ lymphocytes are not required for the pathology resulting from IFN-gamma neutralization. Cytokine measurements on parasite Ag-stimulated spleen cells from mAb-treated mice indicated that both CD4+ and CD8+ cells produce IFN-gamma whereas only CD4+ cells contribute to parasite Ag-induced IL-2 synthesis. Together, these results suggest that CD4+ and CD8+ lymphocytes act additively or synergistically to prevent reactivation of chronic T. gondii infection probably through the production of IFN-gamma.
Gazzinelli
R
R
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
Xu
Y
Y
Hieny
S
S
Cheever
A
A
Sher
A
A
D000818:Animals; D001921:Brain / Q000473:pathology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D016207:Cytokines / Q000096:biosynthesis; D007371:Interferon-gamma / Q000502:physiology; D008213:Lymphocyte Activation; D008212:Lymphocyte Depletion; D051379:Mice; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D014122:Toxoplasma / Q000472:pathogenicity*; D014124:Toxoplasmosis, Animal / Q000276:immunology* / Q000473:pathology
D016827:CD8 Antigens; D016207:Cytokines; D007371:Interferon-gamma