Analysis of the pathogenicity of Acanthamoeba and protective immunity to Acanthamoeba in humans.

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Host immune responses to antigens of two species of free-living amoebae, Acanthamoeba polyphaga (Ap) and A.castellanii (Ac) , were analyzed in humans. Regardless of their past history of acanthamoebiasis, a half of healthy Japanese adults showed significant proliferation of peripheral blood T cells to both Ap and Ac crude antigens in vitro. All the responding T cells tested were CD3^+4^+8^-and TCR-alphabeta^+, and those were functionally of Thl subtype when their cytokine-production profiles were tested. In spite of significant T cell proliferative responses to Ap and Ac, no detectable specific IgG antibodies were observed, suggesting dissociation of cellular and humoral immunity to Acanthamoeba antigens in healthy controls. We tested a probable patient with amoebic meningoencephalitis, however, she showed no detectable T-cell resonses even to the causative amoeba. It was suggested that such a failure of T-cell responses to Acanthamoeba might have been involved in the pathogenesis. We … More analyzed a heterogeneity of human T cell epitopes of Acanthamoeba determined by differencies in genetic background. By using human CD4^+T-cell clones specific for Ap or Ac, we observed the existence of T-cell epitopes shared by both Ap and Ac, or those which were species-specific. Furthermore, it seemed likely that some epitopes were expressed only a part of Acanthamoeba. However, we observed that such a diversity in their epitopes were not directly related to the strength of pathogenicity of Acanthamoeba. Togeter with those results, we would like to conclude that not all, but considerable number of healthy individuals are sensitized with the pathogenic Acanthamoeba resulting induction of Acanthamoeba-specific Thl cell responses. It was likely that those T cells generally recognized a common epitope (s) of the genus Acanthamoeba, however, some T-cell epitopes were heterogenous within a species. Those heterogeneities both in the host immune responses and the amoebic epitopes might have contribution for the immunopathogenicities of acanthamoebiasis in humans. Less