T cell response in murine Leishmanial mexicana amazonensis infection: production of interferon‐γby CD8+ cells

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Abstract
The immune response to Leishmania major has been the subject of many investigations. However, Leishmania includes many species with different clinical manifestations. In this report, we studied the Tcell response to L. mexicana amazonensis, a New World species, in a murine model. We found that, similar to L. major, an Old World species, resistant C57BL/6 mice produced a high level of IFN‐γ and a low level of IL‐4. Conversely, susceptible BALB/c mice produced a much lower level of IFN‐γ and higher level of IL‐4.Although IFN‐γ is one of the important lymphokines that mediate macrophage activation and thus the destruction of the intracellular parasites, which lymphocyte subsets are producing the IFN‐γ is still a controversy. Much evidence including the isolation of protective, IFN‐γ‐producing, CD4+ cell lines have confirmed the participation of CD4+ Thl cells unequivocally. However, both CD4+ and CD8+ cells produced IFN‐γ. Recently, an increasing body of evidence has appeared suggesting that CD8+ cells also play a role in the resolution of murine L. major infection. We found that in the L. m. amazonensis model, when CD8+ lymphocytes from resistant C57BL/6 mice were eliminated by anti‐CD8 antibody and complement‐mediated lysis, the IFN‐γ production was reduced by 77%. This indicated that CD8+ cells produced a significant amount of the IFN‐γ. However, our results also indicate that IFN‐γ production by CD8+ cells was dependent on CD4+ cells.

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