No abstract

The interaction between follicular T helper cells (TFH) and B cells in the lymph nodes and spleen has a major impact on the development of antigen-specific B cell responses during infection or vaccination. Recent studies described a functional equivalent of these cells among circulating CD4 T cells, referred to as peripheral TFH cells. Here, we characterize the phenotype and in vitro B cell helper activity of peripheral TFH populations, as well as the effect of HIV infection on these populations. In co-culture experiments we confirmed CXCR5+ cells from HIV-uninfected donors provide help to B cells and more specifically, we identified a CCR7highCXCR5highCCR6highPD-1high CD4 T cell population that secretes IL-21 and enhances isotype-switched immunoglobulin production. This population is significantly decreased in treatment-naïve, HIV-infected individuals and can be recovered after anti-retroviral therapy. We found impaired immunoglobulin production in co-cultures from HIV-infected individuals and found no correlation between the frequency of peripheral TFH cells and memory B cells, or with neutralization activity in untreated HIV infection in our cohort. Furthermore, we found that within the peripheral TFH population, the expression level of TFH-associated genes more closely resembles a memory, non-TFH population, as opposed to a TFH population. Overall, our data identify a heterogeneous population of circulating CD4 T cells that provides in vitro help to B cells, and challenges the origin of these cells as memory TFH cells.

Application of multiplex bead immunoassays has allowed us to identify distinct patterns of cytokines that relate to both clinical disease and the cellular infiltrates present. Bioinformatics analysis allowed identification of cytokines that differentiate idiopathic uveitis from noninflammatory control AqH and are likely to be important for the pathogenesis of uveitis.

A fundamental mechanism of immune privilege in the eye is the induction of T lymphocyte apoptosis. Intraocular inflammation in uveitis implies compromise of immune privilege. This study sought to determine whether apoptosis of T cells is actively inhibited in patients with uveitis and by what pathways this may occur. Apoptotic lymphocytes were found to be absent from aqueous humor (AqH) of virtually all patients with recent-onset uveitis. However, T cells removed from the eye were highly susceptible to both spontaneous and Fas ligand-induced apoptosis in vitro. AqH from patients with uveitis had no modulatory effect on Fas ligand-induced apoptosis, but strongly suppressed survival factor deprivation-induced apoptosis. In contrast, noninflammatory AqH from patients undergoing cataract surgery had no modulatory effects on apoptosis at all. These data suggest that triggering of the Fas pathway is diminished in uveitis, and also that homeostatic resolution through survival factor deprivation-induced apoptosis is inhibited by factors present in AqH. The most widely recognized pathways, common γ-chain cytokines and type I IFNs, did not contribute to AqH-mediated T cell survival. High levels of both IL-6 and soluble IL-6R were found in AqH. IL-6 alone did not induce T cell survival, because IL-6R expression on T cells in AqH was too low to facilitate signaling. However, combinations of IL-6 and soluble IL-6R were highly effective inhibitors of T cell apoptosis, suggesting that the trans-signaling pathway is likely to be a key mediator of T cell apoptosis inhibition mediated by uveitis AqH.

No abstract

Overexpression of the constitutive chemokine receptor CXCR4 has been shown to contribute to the accumulation of leukocytes at sites of chronic inflammation. Glucocorticoids are widely used to treat inflammatory disorders such as uveitis to considerable effect, yet paradoxically have been reported to increase CXCR4 expression in vitro. We show here that ocular lymphocytes isolated from patients with uveitis who had been treated with topical glucocorticoids expressed highly elevated levels of CXCR4. The up-regulation of CXCR4 could be reproduced in vitro by culture of CD4+ T cells with aqueous humor (AqH), indicating a role for the ocular microenvironment rather than preferential recruitment of CXCR4+ cells. Untreated uveitis and noninflammatory AqH up-regulated CXCR4 to a limited extent; this was dependent on TGF-β2. However, the highest levels of CXCR4 both in vivo and in vitro were found in the glucocorticoid-treated patients. Glucocorticoids appeared to be directly responsible for the induction of CXCR4 in treated patients, as the glucocorticoid receptor antagonist RU38486 inhibited the in vitro up-regulation by AqH from these patients. Dexamethasone selectively up-regulated CXCR4 in vitro, but not any of a wide range of other chemokine receptors. CXCL12, the ligand for CXCR4, was present in AqH under noninflammatory conditions, but the levels were low in untreated uveitis and undetectable in treated uveitis AqH. The importance of these results for the treatment of HIV patients with glucocorticoids is discussed as well as a role for glucocorticoid-induced CXCR4 up-regulation and CXCL12 down-regulation in controlling the migration of lymphocyte populations, resulting in resolution of inflammation.

Vitamin A (VitA) and its derivative retinoic acid (RA) are essential for immunological responses. Acquisition of effector responses is impeded in VitA-deficient (VAD) mice, but little is known about maintenance and expression of previously acquired effector function in the VAD environment, or its impact on progression of autoimmune diseases. We examined this using two models of uveitis: experimental autoimmune uveitis (EAU) induced by active immunization and spontaneous uveitis in retina-specific T cell receptor transgenic (R161H) mice, and in the model of experimental autoimmune encephalomyelitis (EAE). VAD was induced by dietary lack of VitA from before birth, or by daily injections of a pan-RA receptor inhibitor BMS493 in adult mice fed with standard diet. VAD mice were essentially resistant to induction of EAU or EAE and displayed impaired effector T cell responses. Defective priming/acquisition of effector function by VAD T cells was also evident in vitro. Interestingly, however, effector T cells primed in a VitA-sufficient environment were able to function in VAD recipients and induced EAU. Furthermore, spontaneously uveitic R161H mice fed with VAD diet, in which priming of pathogenic T cells occurs before onset of full VitA deficiency, appeared to develop unreduced or even exacerbated spontaneous uveitis compared to VitA-sufficient R161H mice. We conclude that although priming of naïve T cells in the VAD environment is defective, effector function acquired under VitA-sufficient conditions is maintained and can be expressed under VAD conditions. Because dietary lack of VitA is rarely profound and may be seasonal, our findings may shed light on immunity and autoimmunity in geographical regions where dietary VitA is limiting.