Type-I interferon (IFN-I) has been increasingly implicated in HIV-1 pathogenesis. Various studies have shown elevated IFN-I and an IFN-I-induced gene and protein expression signature in HIV-1 infection, yet the elevated IFN-I species has not been conclusively identified, its source remains obscure and its role in driving HIV-1 pathogenesis is controversial. We assessed IFN-I species in plasma by ELISAs and bioassay, and we investigated potential sources of IFN-I in blood and lymph node tissue by qRT-PCR. Furthermore, we measured the effect of therapeutic administration of IFNα in HCV-infected subjects to model the effect of IFNα on chronic immune activation. IFN-I bioactivity was significantly increased in plasma of untreated HIV-1-infected subjects relative to uninfected subjects (p = 0.012), and IFNα was the predominant IFN-I subtype correlating with IFN-I bioactivity (r = 0.658, p<0.001). IFNα was not detectable in plasma of subjects receiving anti-retroviral therapy. Elevated expression of IFNα mRNA was limited to lymph node tissue cells, suggesting that peripheral blood leukocytes are not a major source of IFNα in untreated chronic HIV-1 infection. Plasma IFN-I levels correlated inversely with CD4 T cell count (p = 0.003) and positively with levels of plasma HIV-1 RNA and CD38 expression on CD8 T cells (p = 0.009). In hepatitis C virus-infected subjects, treatment with IFN-I and ribavirin increased expression of CD38 on CD8 T cells (p = 0.003). These studies identify IFNα derived from lymph nodes, rather than blood leukocytes, as a possible source of the IFN-I signature that contributes to immune activation in HIV-1 infection.

SummaryInflammatory bowel disease (IBD) is characterized by damage to the gut mucosa and systemic inflammation. We sought to evaluate the role of chronic inflammation on circulating T-cell activation in human subjects with Crohn's disease and ulcerative colitis. We studied 54 patients with IBD and 28 healthy controls. T-cell activation and cycling were assessed in whole blood samples by flow cytometry. Levels of lipopolysaccharide (LPS) were measured in serum by Limulus amoebocyte lysate assay, and plasma levels of inflammatory markers and LPS-binding proteins were measured by ELISA. The proportions of circulating CD4 + and CD8 + T lymphocytes in cycle (Ki67 + ) are increased in patients with IBD compared with these proportions in controls. CD8 + T cells from patients with IBD are also enriched for cells that expressed CD38 and HLA-DR, and proportions of these cells are related to plasma levels of interleukin-6 and C-reactive protein in these patients. Intracellular interleukin-2 and interferon-c levels were elevated in resting and polyclonally activated CD4 + and CD8 + T cells in patients with IBD when compared with levels from healthy controls. Surprisingly, we did not find increased levels of LPS in the serum of patients with IBD. We did, however, find a signature of recent microbial translocation, as levels of LPS-binding protein are increased in the plasma of patients with IBD compared with plasma levels in healthy controls; LPS-binding protein levels are also directly related to proportions of CD38 HLA-DR-expressing CD4 + and CD8 + T cells. Local damage to the gastrointestinal tract in IBD may result in systemic inflammation and T-cell activation.

CTL are endowed with the ability to eliminate pathogens through perforin-mediated cytotoxic activity. The mechanism for perforin-mediated Ag-specific killing has been solely attributed to cytotoxic granule exocytosis from activated CD8+ T cells. In this study, we redefine this mechanism, demonstrating that virus-specific CD8+ T cells rapidly up-regulate perforin in response to stimulation temporally with IFN-γ and CD107a expression. Following Ag-specific activation, newly synthesized perforin rapidly appears at the immunological synapse, both in association with and independent of cytotoxic granules, where it functions to promote cytotoxicity. Our work suggests a novel mechanism of CTL cytotoxicity and identifies a novel correlate of CD8+ T cell-mediated immunity.

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