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Defining the minimal thresholds for effective antiviral T cell immunity is important for clinical decisions in immunodeficient patients. TCR signaling is critical for T cell development, activation, and effector functions. In this article, we analyzed which of these TCR-mediated processes is limiting for antiviral immunity in a mouse strain with reduced expression of SLP-76 (twp mice). Despite severe T cell activation defects in vitro, twp mice generated a normal proportion of antiviral effector T cells postinfection with lymphocytic choriomeningitis virus (LCMV). Twp CD8(+) T cells showed impaired polyfunctional cytokine production, whereas cytotoxicity as the crucial antiviral effector function for LCMV control was normal. The main limiting factor in the antiviral response of twp mice was impaired T cell proliferation and survival, leading to a 5- to 10-fold reduction of antiviral T cells at the peak of the immune response. This was still sufficient to control infection with the LCMV Armstrong strain, but the more rapidly replicating LCMV-WE induced T cell exhaustion and viral persistence. Thus, under conditions of impaired TCR signaling, reduced T cell expansion was the limiting factor in antiviral immunity. These findings have implications for understanding antiviral immunity in patients with T cell deficiencies., (Copyright © 2015 by The American Association of Immunologists, Inc.)

Familial hemophagocytic lymphohistiocytosis (FHL) is a hyperinflammatory syndrome affecting patients with genetic cytotoxicity defects. Perforin‐deficient (PKO) mice recapitulate the full clinical picture of FHL after infection with lymphocytic choriomeningitis virus (LCMV). Hyperactivated CD8+ T cells and IFN‐γ have been identified as the key drivers of FHL and represent targets for therapeutic interventions. However, the response of patients is variable. This could be due to trigger‐dependent differences in pathogenesis, which is difficult to address in FHL patients, since the trigger frequently escapes detection. We established an alternative FHL model using intravenous infection of PKO mice with murine CMV (MCMV)Smith. PKO mice developed acute FHL after both infections and fulfilled HLH diagnostic criteria accompanied by excessive IFN‐γ production by disease‐inducing T cells, that enrich in the BM. However, direct comparison of the two infection models disclosed trigger‐dependence of FHL progression and revealed a higher contribution of CD4 T cells and NK cells to IFN‐γ production after MCMV infection. Importantly, therapeutic intervention by IFN‐γ neutralization or CD8+ T‐cell depletion had less benefit in MCMV‐triggered FHL compared to LCMV‐triggered FHL, likely due to MCMV‐induced cytopathology. Thus, the context of the specific triggering viral infection can impact the success of targeted immunotherapeutic HLH control. [ABSTRACT FROM AUTHOR]