Multiple inhibitory molecules create a profoundly immunuosuppressive environment during chronic viral infections in humans and mice. Therefore, eliciting effective immunity in this context represents a challenge. Here we report that during a murine chronic viral infection, interleukin-6 (IL-6) was produced by irradiation resistant cells in a biphasic manner, with late IL-6 being absolutely essential for viral control. The underlying mechanism involved IL-6 signaling on virus-specific CD4 T cells that caused up-regulation of the transcription factor Bcl6 and enhanced T follicular helper (Tfh) cell responses at late, but not early, stages of chronic viral infection. This resulted in escalation of germinal center reactions and improved antibody responses. Our results uncover an antiviral strategy that helps to safely resolve a persistent infection in vivo.

SUMMARY Emerging in vitro and epidemiological studies indicate an association between virally-induced impaired type I interferon (IFN-I) production and enhanced susceptibility to opportunistic infections, which represent a major health problem. Here, we provide in vivo evidence that lymphocytic choriomeningitis virus (LCMV) infection of its natural host, the mouse, dramatically diminishes the unique capacity of plasmacytoid dendritic cells (pDCs) to secrete high levels of systemic IFN-I. While both acute and persistent LCMV infections suppress pDC IFN-I response, only the persistent virus induces a long-lasting diversion of this innate immune pathway. LCMV infection selectively affects the hallmark function of pDCs to produce prodigious amounts of IFN-I but does not alter their secretion of other cytokines, chemokines and maturation. This results in reduced IFN-I production and relates to impaired NK cell responses in LCMV-infected mice challenged with murine cytomegalovirus (MCMV) as an opportunistic pathogen. This innate immune-defect is associated with a compromised host ability to counteract early MCMV spread. Thus, an explanation for understanding the occurrence of opportunistic infections following in vivo viral insults is uncovered and has important implications for the alleviation and treatment of such medical complications.

The circadian system regulates numerous physiological processes including immune responses. Here, we show that mice deficient of the circadian clock genes and [ double knockout (DKO)] develop an autoimmune phenotype including high serum IgG concentrations, serum antinuclear antibodies, and precipitation of IgG, IgM, and complement 3 in glomeruli and massive infiltration of leukocytes into the lungs and kidneys. Flow cytometry of lymphoid organs revealed decreased pre-B cell numbers and a higher percentage of mature recirculating B cells in the bone marrow, as well as increased numbers of B2 B cells in the peritoneal cavity of DKO mice. The B cell receptor (BCR) proximal signaling pathway plays a critical role in autoimmunity regulation. Activation of DKO splenic B cells elicited markedly enhanced tyrosine phosphorylation of cellular proteins compared with cells from control mice, suggesting that overactivation of the BCR-signaling pathway may contribute to the autoimmunity phenotype in the DKO mice. In addition, the expression of, the deficiency of which contributes to the pathogenesis of systemic lupus erythematosus, was significantly down-regulated in DKO B cells. Our results suggest that B cell development, the BCR-signaling pathway, and expression are regulated by circadian clock CRY proteins and that their dysregulation through loss of CRY contributes to autoimmunity.

Talin, a cytoskeletal protein essential in mediating integrin activation, has been previously shown to be involved in the regulation of T cell proliferation and function. Here we describe a role for talin in maintaining the homeostasis and survival of the regulatory T (Treg) cell pool. T cell-specific deletion of talin in Tln1fl/flCd4Cre mice resulted in spontaneous lymphocyte activation, primarily due to numerical and functional deficiencies of Treg cells in the periphery. Peripheral talin-deficient Treg cells were unable to maintain high expression of IL-2Rα, resulting in impaired IL-2 signaling and ultimately leading to increased apoptosis through downregulation of pro-survival proteins Bcl-2 and Mcl-1. The requirement for talin in maintaining high IL-2Rα expression by Treg cells was due, in part, to integrin LFA-1-mediated interactions between Treg cells and dendritic cells. Collectively, our data suggest a critical role for talin in Treg cell-mediated maintenance of immune homeostasis.

Circadian rhythms are defined as 24 hour oscillations in physiological and behavioral processes. Clinical data suggests circadian involvement in the predisposition and progression of immune-related morbidities such as cancer and autoimmune disease. Recent studies have demonstrated the direct role of core molecular clock components in maintaining the immune system. A subset of CD4+ T cells known as regulatory T cells (Treg) are critical for preserving balance in the immune system and have been shown to be able to prevent a broad range of autoimmune disease. By studying the role of core circadian genes in Treg cells the connection between the circadian clock and autoimmune disease may be further elucidated. We have identified a core circadian clock gene, cryptochrome (Cry), to have a role in Treg cell function both in vitro and in vivo. The deficiency of Cry in Treg cells results in a breakdown in immune tolerance, which results in severe pathological autoimmunity in mice. This is characterized by immune cell infiltration into peripheral tissues as well as increased numbers of cytokine producing CD4 and CD8 T cells. It was also seen that ectopic expression of Cry in Treg cells results in increased suppression of T cell proliferation in vitro. Thus, we have demonstrated a direct role of Cry expression in the function of Treg cells.