Caspase-8 (casp8) is required for extrinsic apoptosis, and mice deficient in casp8 fail to develop and die in utero while ultimately failing to maintain the proliferation of T cells, B cells, and a host of other cell types. Paradoxically, these failures are not caused by a defect in apoptosis, but by a presumed proliferative function of this protease. Indeed, following mitogenic stimulation, T cells lacking casp8 or its adaptor protein FADD (Fas-associated death domain protein) develop a hyperautophagic morphology, and die a programmed necrosis-like death process termed necroptosis. Recent studies have demonstrated that receptor-interacting protein kinases (RIPKs) RIPK1 and RIPK3 together facilitate TNFinduced necroptosis, but the precise role of RIPKs in the demise of T cells lacking FADD or casp8 activity is unknown. Here we demonstrate that RIPK3 and FADD have opposing and complementary roles in promoting T-cell clonal expansion and homeostasis. We show that the defective proliferation of T cells bearing an interfering form of FADD (FADDdd) is rescued by crossing with RIPK3 −/− mice, although such rescue ultimately leads to lymphadenopathy. Enhanced recovery of these double-mutant T cells following stimulation demonstrates that FADD, casp8, and RIPK3 are all essential for clonal expansion, contraction, and antiviral responses. Finally, we demonstrate that caspase-mediated cleavage of RIPK1-containing necrosis inducing complexes (necrosomes) is sufficient to prevent necroptosis in the face of death receptor signaling. These studies highlight the "two-faced" nature of casp8 activity, promoting clonal expansion in some situations and apoptotic demise in others.

The functional role of the ELR+ chemokine CXCL1 in host defense and disease following infection of the CNS with the neurotropic JHM strain of mouse hepatitis virus (JHMV) was examined. Mice in which expression of CXCL1 is under the control of a tetracycline-inducible promoter active within GFAP-positive cells were generated and this allowed for selectively increasing CNS expression of CXCL1 in response to JHMV infection and evaluating the effects on neuroinflammation, control of viral replication, and demyelination. Inducible expression of CNS-derived CXCL1 resulted in increased levels of CXCL1 protein within the serum, brain and spinal cord that correlated with increased frequency of Ly6G+CD11b+ neutrophils present within the CNS. Elevated levels of CXCL1 did not influence the generation of virus-specific T cells and there was no difference in control of JHMV replication compared to control mice indicating T cell infiltration into the CNS is CXCL1-independent. Sustained CXCL1 expression within the CNS resulted in increased mortality that correlated with elevated neutrophil infiltration, diminished numbers of mature oligodendrocytes, and an increase in the severity of demyelination. Neutrophil ablation in CXCL1-transgenic mice reduced the severity of demyelination in mice arguing a role for these cells in white matter damage. Collectively, these findings illustrate that sustained CXCL1 expression amplifies the severity of white matter damage and neutrophils can contribute to this process in a model of viral-induced neurologic disease.

Blockade of IFN-α but not IFN-β signaling using either an antibody or a selective S1PR1 agonist, CYM-5442, prevented type 1 diabetes (T1D) in the mouse Rip-LCMV T1D model. First, treatment with antibody or CYM-5442 limited the migration of autoimmune "antiself" T cells to the external boundaries around the islets and prevented their entry into the islets so they could not be positioned to engage, kill, and thus remove insulin-producing β cells. Second, CYM-5442 induced an exhaustion signature in antiself T cells by up-regulating the negative immune regulator receptor genes Pdcd1, Lag3, Ctla4, Tigit, and Btla, thereby limiting their killing ability. By such means, insulin production was preserved and glucose regulation maintained, and a mechanism for S1PR1 immunomodulation described.type I interferon | IFN-alpha | S1PR1 | type 1 diabetes T ype 1 diabetes (T1D) is an autoimmune disorder defined by infiltration of autoreactive lymphoid cells into the islets of Langerhans that destroy insulin-producing β cells (1). By the time of clinical diagnosis, T cells have destroyed 60-80% or more of total β cells, resulting in high blood glucose levels as a result of low insulin production. Prevention of ketoacidosis and death require lifelong delivery of exogenous insulin. However, daily insulin therapy is associated with increased prevalence of debilitating pathologies of cardiovascular, central and peripheral nervous, ophthalmic, and peripheral vascular systems among others.A role for type I IFN in autoimmune disease was first reported by Notkins' laboratory (2) and pancreata removed at necropsy from humans with T1D displayed significant increases in type I IFN (3, 4). Treatment of humans having hairy cell leukemia (5) or hepatitis C virus (6) with IFN-α was associated with induction or acceleration of the diabetogenic process, and recent longitudinal studies demonstrated that a IFN-I gene signature of individuals at risk for developing T1D preceded clinical onset (7,8). Direct evidence for an association of IFN-I with T1D was shown by Stewart et al. (9) in transgenic (tg) mice and strengthened in studies with NOD mice (10, 11). Unanue and coworkers (10) found IFN-I transcriptional signatures within the islets preceded T-cell activation. McDevitt and coworkers (11) reported treatment of 2-to 3-wk-old NOD mice with antibody to IFNAR1 delayed the onset and decreased the incidence of T1D. Using the virusinduced Rip-LCMV T1D model, Zinkernagel and coworkers (12) demonstrated that genetic ablation of Ifnar could delay onset of T1D. However, the mechanism of action by type I IFN was unknown. Here, we report studies that define the species of type I IFN and mechanism involved causing T1D and therapeutic approaches to prevent diabetes by preserving β-cell function. Results and DiscussionTo uncover the pathological role(s) of IFN-I, a viral mouse model of T1D (13) was used in which several parameters mimic immunological and histopathological components of human T1D and the "self" antigen recognized by specific autoimmune T cells ca...

Increasing evidence points to an important role for neutrophils in participating in the pathogenesis of the human demyelinating disease MS and the animal model EAE. Therefore, a better understanding of the signals controlling migration of neutrophils as well as evaluating the role of these cells in demyelination is important to define cellular components that contribute to disease in MS patients. In this study, we examined the functional role of the chemokine CXCL1 in contributing to neuroinflammation and demyelination in EAE. Using transgenic mice in which expression of CXCL1 is under the control of a tetracycline‐inducible promoter active within glial fibrillary acidic protein‐positive cells, we have shown that sustained CXCL1 expression within the CNS increased the severity of clinical and histologic disease that was independent of an increase in the frequency of encephalitogenic Th1 and Th17 cells. Rather, disease was associated with enhanced recruitment of CD11b+Ly6G+ neutrophils into the spinal cord. Targeting neutrophils resulted in a reduction in demyelination arguing for a role for these cells in myelin damage. Collectively, these findings emphasize that CXCL1‐mediated attraction of neutrophils into the CNS augments demyelination suggesting that this signaling pathway may offer new targets for therapeutic intervention.

Chemokines (chemotactic cytokines) are involved in a wide variety of biological processes. Following microbial infection, there is often robust chemokine signaling elicited from infected cells, which contributes to both innate and adaptive immune responses that control growth of the invading pathogen. Infection of the central nervous system (CNS) by the neuroadapted John Howard Mueller (JHM) strain of mouse hepatitis virus (JHMV) provides an excellent example of how chemokines aid in host defense as well as contribute to disease. Intracranial inoculation of the CNS of susceptible mice with JHMV results in an acute encephalomyelitis characterized by widespread dissemination of virus throughout the parenchyma. Virus-specific T cells are recruited to the CNS, and control viral replication through release of antiviral cytokines and cytolytic activity. Sterile immunity is not acquired, and virus will persist primarily in white matter tracts leading to chronic neuroinflammation and demyelination. Chemokines are expressed and contribute to defense as well as chronic disease by attracting targeted populations of leukocytes to the CNS. The T cell chemoattractant chemokine CXCL10 (interferon-inducible protein 10 kDa, IP-10) is prominently expressed in both stages of disease, and serves to attract activated T and B lymphocytes expressing CXC chemokine receptor 3 (CXCR3), the receptor for CXCL10. Functional studies that have blocked expression of either CXCL10 or CXCR3 illuminate the important role of this signaling pathway in host defense and neurodegeneration in a model of viral-induced neurologic disease.