The Role of CD8+T Cells in the Immune Response to Trypanosoma Cruzi in Mice Held at Elevated Environmental Temperature
When maintained at 36°C, T. cruzi infected C3H mice survive an infection that is lethal to mice maintained at room temperature. To study the role of CD8+ T cells in this phenomenon, anti-CD8 monoclonal antibody (MAb) was used to deplete CD8+ T cells in vivo. An IgG2a-producing rat hybridoma (designated 53-6.72) was adapted to serum free medium, and anti-CD8 MAb was purified from culture supernatant by ammonium sulfate precipitation. Mice were injected intraperitoneally with 200(ig of MAb for three consecutive days. On the fifth day, the result of the in vivo depletion of CD8+ T cells was determined by an indirect immunofluorescence assay and was found to be approximately 95%. Mice were then infected with 103 blood-form trypomastigotes. Parasitemia and longevity were monitored. The results indicated that anti-CD8 MAb treated infected mice developed higher parasitemia levels and higher mortality as compared to normal IgG treated mice at both temperatures. Parasites began to appear in the peripheral blood of anti-CD8 MAb treated infected mice on approximately day 13 of infection when mice were maintained at room temperature but not until approximately day 20 of infection when anti-CD8 treated infected mice were held at elevated environmental temperature. The parasitemia levels of anti-CD8 MAb treated infected mice held at room temperature reached a peak at 1.12 X 107 parasites per ml of blood, whereas those held at elevated environmental temperature reached a peak parasitemia of 1.10 X 10 7. Parasitemia levels in normal IgG-treated infected mice at room temperature reached a peak of 1.02 X 107 parasites per ml of blood whereas parasitemia levels in normal IgG treated infected mice held at elevated environmental temperature only reached 3.1 X 105 per ml of blood by day 53 of infection. All anti-CD8 MAb treated infected mice at room temperature died by day 27 of infection, whereas those held at elevated environmental temperature died by day 35. All normal IgG-treated infected mice at room temperature died by day 36 of infection. However, all normal IgG-treated infected mice held at elevated environmental temperature were still alive by day 53 of infection. The results of this study suggest that CD8+ T cells play a significant role in the immune response to T. cruzi in mice maintained at elevated environmental temperature. Depletion of CD8+ T cells from mice by administration of anti-CD8 MAb resulted in an abrogation of the protective effects of elevated environmental temperature on Trypanosoma cruzi infection.
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