Oleic acid enhances proliferation and calcium mobilization of CD3/CD28 activated CD4+ T cells through incorporation into membrane lipids.

Unsaturated fatty acids (UFA) are crucial for T-cell effector functions, as they can affect the growth, differentiation, survival, and function of T cells. Nonetheless, the mechanisms by which UFA affects T-cell behavior are ill-defined. Therefore, we analyzed the processing of oleic acid, a prominent UFA abundantly present in blood, adipocytes, and the fat pads surrounding lymph nodes, in CD4+ T cells. We found that exogenous oleic acid increases proliferation and enhances the calcium flux response upon CD3/CD28 activation. By using a variety of techniques, we found that the incorporation of oleic acid into membrane lipids, rather than regulation of cellular metabolism or TCR expression, is essential for its effects on CD4+ T cells. These results provide novel insights into the mechanism through which exogenous oleic acid enhances CD4+ T-cell function.

Hyaluronidase treatment of synovial fluid is required for accurate detection of inflammatory cells and soluble mediators.

BACKGROUND: Synovial fluid (SF) is commonly used for diagnostic and research purposes, as it is believed to reflect the local inflammatory environment. Owing to its complex composition and especially the presence of hyaluronic acid, SF is usually viscous and non-homogeneous. In this study, we investigated the importance of homogenization of the total SF sample before subsequent analysis. METHODS: SF was obtained from the knee of 29 arthritis patients (26 rheumatoid arthritis, 2 osteoarthritis, and 1 juvenile idiopathic arthritis patient) as part of standard clinical care. Synovial fluid was either treated with hyaluronidase as a whole or after aliquoting to determine whether the concentration of soluble mediators is evenly distributed in the viscous synovial fluid. Cytokine and IgG levels were measured by ELISA or Luminex and a total of seven fatty acid and oxylipin levels were determined using LC-MS/MS in all aliquots. For cell analysis, synovial fluid was first centrifuged and the pellet was separated from the fluid. The fluid was subsequently treated with hyaluronidase and centrifuged to isolate remaining cells. Cell numbers and phenotype were determined using flow cytometry. RESULTS: In all patients, there was less variation in IgG, 17-HDHA, leukotriene B4 (LTB4), and prostaglandin E2 (PGE2) levels when homogenization was performed before aliquoting the SF sample. There was no difference in variation for cytokines, 15-HETE, and fatty acids arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Between 0.8 and 70% of immune cells (median 5%) remained in suspension and were missing in subsequent analyses when the cells were isolated from untreated SF. This percentage was higher for T and B cells: 7-85% (median 22%) and 7-88% (median 23 %), respectively. CONCLUSIONS: Homogenization of the entire SF sample leads to less variability in IgG and oxylipin levels and prevents erroneous conclusions based on incomplete isolation of synovial fluid cells.

Defective control of vitamin D receptor-mediated epithelial STAT1 signalling predisposes to severe respiratory syncytial virus bronchiolitis.

Respiratory syncytial virus (RSV) infection causes bronchiolitis in infants with seasonal frequency, for which vitamin D deficiency and a well-described polymorphism in the vitamin D receptor (VDR) FokI are important risk factors. Recent studies suggest that vitamin D regulates immune pathways in airway epithelial cells during RSV infection. It is not understood why the VDR FokI polymorphism predisposes to severe RSV bronchiolitis. We investigated how the VDR FokI polymorphism regulates the epithelial response to RSV infection. To this end, we over-expressed the normal and FokI VDR variants in A549 airway epithelial cells. Vitamin D restrained the expression of both NFκB- and STAT1-induced antiviral genes. However, while NFκB control by vitamin D remained intact, both RSV-induced phosphorylation of STAT1 and expression of its downstream targets, IRF1 and IRF7, escaped vitamin D control in FokI epithelial cells. The poor capacity of vitamin D to regulate IRF1 in FokI VDR-expressing cells was recapitulated using blood samples from normal and FokI VDR-genotyped healthy donors. Hence, we provide mechanistic insight that the FokI VDR polymorphism renders STAT1-mediated antiviral immune reactions to RSV infection non-responsive to vitamin D control, resulting in enhanced immunopathology and exacerbated RSV bronchiolitis.