Mechanisms of IFNγ regulation of autoimmune myocarditis

A protective effect of interferon-gamma (IFNγ) has been described in a number of models of autoimmune disease, including experimental autoimmune myocarditis (EAM). Some reports have suggested that regulation of apoptosis in autoreactive lymphocytes mediate these protective functions. We examined the potential of IFNγ to regulate apoptotic mechanisms in detail, both in vitro and in vivo in EAM. We observed multiple apoptotic defects in caspase activity, and the expression of TNF superfamily members on CD4⁺ T cells. In addition, we observed selective defects in CD4⁺ T cell activation in response to antigenic stimulation. These activation and apoptotic defects were CD4⁺ cell autonomous, independent of the genotype of APCs. Inhibition of nitric oxide production in vivo did not reproduce the severe form of EAM of IFNγ-deficient mice, indicating that this pathway does not mediate the protective effect of IFNγ. Crosswise adoptive transfer of wild type, IFNγ^-/- and IFNγR^-/- EAM demonstrated that IFNγ signaling was critical in CD4⁺ cells, but that non-CD4⁺ sources of IFNγ production were also involved in the control of disease. Together, these data indicate multiple mechanisms of autonomous and non-autonomous CD4⁺ T cell regulation mediated by IFNγ in the control of autoimmune heart disease.