The SA85-1.1 protein of the Trypanosoma cruzi trans-sialidase superfamily is a dominant T-cell antigen.

Trypanosoma cruzi currently infects 18 million people, and 30% of those infected develop a chronic inflammatory process that causes significant morbidity or mortality. The major histocompatibility complex class II (MHC-II)-restricted T-cell response is critical to the control of the infection and to the ensuing inflammatory pathology. The specific epitopes or major antigens of this response have not been identified. The parasite simultaneously expresses variant members of the trans-sialidase superfamily. To begin to analyze the MHC-II response to these variant proteins, the response to a single surface protein, SA85-1.1, was initiated. These studies have demonstrated that a biased gamma interferon (IFN-gamma) response to the SA85-1.1 protein develops during T. cruzi infection. In addition, adoptive transfer of a CD4 clone that recognizes an SA85-1.1 epitope, named epitope 1, and immunization with a peptide encoding epitope 1 were protective and suggested that epitope 1 may be immunodominant. In this report IFN-gamma intracellular staining demonstrated that splenocytes from acutely and chronically infected mice, incubated with SA85-1.1 protein or peptides that encode epitope 1, result in IFN-gamma synthesis by 4 to 6% of the splenic CD4 cells. These data indicate that during T. cruzi infection epitope 1 is a major epitope and that 4 to 6% of the CD4 cells are stimulated by a single trans-sialidase superfamily epitope and suggest that a combination of trans-sialidase superfamily proteins combines to stimulate a majority of CD4 cells. These data suggest that during T. cruzi infection the CD4 response to the trans-sialidase superfamily is critical to the protective response and to the ensuing chronic inflammatory pathology.

Trypanosoma cruzi: the effect of nitric oxide synthesis inhibition on the CD4 T cell response to the trans-sialidase superfamily.

During Trypanosoma cruzi infection the trans-sialidase superfamily stimulates the development of a large population of CD4 T lymphocytes that produces IFNgamma. These CD4 T cells fail to proliferate when stimulated in vitro. Why they fail to proliferate remains unclear. Nitric oxide is a critical component of the host immune response against T. cruzi, and to determine if NO inhibits trans-sialidase superfamily-specific proliferative responses, mice were fed either N(G)-nitro-L-arginine methylester (L-NAME), an inhibitor of inducible nitric oxide synthase (iNOS), or N(G)-nitro-D-arginine methyl ester (D-NAME), an inactive analog of L-NAME. The L-NAME-fed mice had increased parasitemia and mortality compared to the D-NAME-fed mice. Following stimulation with a T. cruzi trans-sialidase superfamily protein, splenocytes from both groups of mice failed to proliferate but continued to make similar amounts of IFNgamma, suggesting that the development of the trans-sialidase superfamily-specific CD4 response was not affected by iNOS inhibition. In addition, IL-2 receptor (IL-2R) expression was increased on T cells isolated from L-NAME-fed mice. These data suggest that during T. cruzi infection NO causes downregulation of IL-2R expression, but does not cause inhibition of trans-sialidase superfamily-specific CD4 T cell proliferation. Rather, the trans-sialidase superfamily proliferation may be inhibited by epitope variation.

The surface protein superfamily of Trypanosoma cruzi stimulates a polarized Th1 response that becomes anergic.

Trypanosoma cruzi is an obligate intracellular parasite that chronically infects mammals. Extracellular mammalian stage trypomastigotes simultaneously express and release multiple members of the parasite's surface protein superfamily; these extracellular proteins should stimulate MHC class II-restricted CD4 T cells. The surface protein superfamily, however, encodes variant epitopes that may inhibit this CD4 response. In this report the surface protein-specific CD4 response was investigated. CD4 cells isolated from acutely and chronically infected mice did not proliferate when stimulated with surface proteins. Adoptive transfer of surface protein-specific CD4 clones or immunization with a peptide encoding a surface protein T cell epitope protected mice during T. cruzi infection. These data strongly suggested that surface proteins were expressed and presented to CD4 cells during infection. Limiting dilution analysis identified an expanded population of surface protein-specific CD4 cells during the acute and chronic infection. These surface protein-specific CD4 cells did not produce IL-2 or IL-4, but did produce IFN-gamma. Enzyme-linked immunospot analyses confirmed that many of the surface protein-specific CD4 cells produce IFN-gamma. Together these results suggest that during T. cruzi infection a potentially protective CD4 response becomes anergic. It is possible that this anergy is induced by variant T cell epitopes encoded by the surface protein superfamily.

T-Cell responses during Trypanosoma brucei infections in mice deficient in inducible nitric oxide synthase.

We have investigated the possibility that nitric oxide (NO) synthesis may affect the course of a trypanosome infection via T-cell responses using mice deficient in inducible NO synthase (iNOS). Parasitemia levels increased at the same rate in both iNOS-deficient homozygous and control heterozygous mice, and peak parasitemia values were the same in both groups. However, the heterozygous mice maintained higher parasitemia levels after the peak of an infection than the homozygous mice due to a decrease in the rate of clearance of parasites. In iNOS-deficient mice there was an increase in the numbers of total CD4(+) cells and activated (interleukin-2 receptor-expressing) CD4(+) cells in infected mice compared with the numbers in uninfected mice. Spleen cells from infected iNOS-deficient mice displayed increased proliferative responses and gamma interferon secretion when stimulated in vitro than those of control mice. These data suggest that NO production depresses T-helper 1-like responses generated during Trypanosoma brucei infections, thus promoting the survival of the parasite.