Phosphatidylserine-positive extracellular vesicles boost effector CD8+ T cell responses during viral infection.

CD8+ T cells are crucial for the clearance of viral infections. During the acute phase, proinflammatory conditions increase the amount of circulating phosphatidylserine+ (PS) extracellular vesicles (EVs). These EVs interact especially with CD8+ T cells; however, it remains unclear whether they can actively modulate CD8+ T cell responses. In this study, we have developed a method to analyze cell-bound PS+ EVs and their target cells in vivo. We show that EV+ cell abundance increases during viral infection and that EVs preferentially bind to activated, but not naive, CD8+ T cells. Superresolution imaging revealed that PS+ EVs attach to clusters of CD8 molecules on the T cell surface. Furthermore, EV-binding induces antigen (Ag)-specific TCR signaling and increased nuclear translocation of the transcription factor Nuclear factor of activated T-cells (NFATc1) in vivo. EV-decorated but not EV-free CD8+ T cells are enriched for gene signatures associated with T-cell receptor signaling, early effector differentiation, and proliferation. Our data thus demonstrate that PS+ EVs provide Ag-specific adjuvant effects to activated CD8+ T cells in vivo.

Microbial influences on epithelial integrity and immune function as a basis for inflammatory diseases.

Certain autoimmune diseases as well as asthma have increased in recent decades, particularly in developed countries. The hygiene hypothesis has been the prevailing model to account for this increase; however, epidemiology studies also support the contribution of diet and obesity to inflammatory diseases. Diet affects the composition of the gut microbiota, and recent studies have identified various molecules and mechanisms that connect diet, the gut microbiota, and immune responses. Herein, we discuss the effects of microbial metabolites, such as short chain fatty acids, on epithelial integrity as well as immune cell function. We propose that dysbiosis contributes to compromised epithelial integrity and disrupted immune tolerance. In addition, dietary molecules affect the function of immune cells directly, particularly through lipid G-protein coupled receptors such as GPR43.

Regulation of inflammatory responses by gut microbiota and chemoattractant receptor GPR43.

The immune system responds to pathogens by a variety of pattern recognition molecules such as the Toll-like receptors (TLRs), which promote recognition of dangerous foreign pathogens. However, recent evidence indicates that normal intestinal microbiota might also positively influence immune responses, and protect against the development of inflammatory diseases. One of these elements may be short-chain fatty acids (SCFAs), which are produced by fermentation of dietary fibre by intestinal microbiota. A feature of human ulcerative colitis and other colitic diseases is a change in 'healthy' microbiota such as Bifidobacterium and Bacteriodes, and a concurrent reduction in SCFAs. Moreover, increased intake of fermentable dietary fibre, or SCFAs, seems to be clinically beneficial in the treatment of colitis. SCFAs bind the G-protein-coupled receptor 43 (GPR43, also known as FFAR2), and here we show that SCFA-GPR43 interactions profoundly affect inflammatory responses. Stimulation of GPR43 by SCFAs was necessary for the normal resolution of certain inflammatory responses, because GPR43-deficient (Gpr43(-/-)) mice showed exacerbated or unresolving inflammation in models of colitis, arthritis and asthma. This seemed to relate to increased production of inflammatory mediators by Gpr43(-/-) immune cells, and increased immune cell recruitment. Germ-free mice, which are devoid of bacteria and express little or no SCFAs, showed a similar dysregulation of certain inflammatory responses. GPR43 binding of SCFAs potentially provides a molecular link between diet, gastrointestinal bacterial metabolism, and immune and inflammatory responses.

Transcriptional stability of cultured cells upon prion infection.

Prion infections induce severe disruption of the central nervous system with neuronal vacuolation and extensive glial reactions, and invariably lead to death of affected individuals. The molecular underpinnings of these events are not well understood. To better define the molecular consequences of prion infections, we analyzed the transcriptional response to persistent prion infection in a panel of three murine neural cell lines in vitro. Colony spot immunochemistry assays indicated that 65-100% of cells were infected in each line. Only the Nav1 gene was marginally modulated in one cell line, whereas transcripts previously reported to be derailed in prion-infected cells were not confirmed in the present study. We attribute these discrepancies to the experimental stringency of the current study, which was performed under conditions designed to minimize potential genetic drifts. These findings are at striking variance with gene expression studies performed on whole brains upon prion infections in vivo, suggesting that many of the latter changes represent secondary reactions to infection. We conclude that, surprisingly, there are no universal transcriptional changes induced by prion infection of neural cells in vitro.