Browsing School, Graduate by Subject "T-Lymphocytes, Regulatory"
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Direct Suppression by Healthy and SLE Human Tregs of B cell Immunoglobulin SecretionRegulatory T cells (Tregs) are characterized by their role in maintaining peripheral self-tolerance and immune homeostasis. One such role is regulation of the humoral response, which is most clearly demonstrated by abundant auto-antibody production in Scurfin mice and IPEX patients, both of which lack functional Tregs. Indirect Treg regulation of the humoral response via their influence on helper T cells, in particular in germinal centers, is well established. Prior demonstration of direct Treg inhibition of B cells has also been demonstrated, primarily in mice, but is mostly attributable to Treg killing of B cells. This regulation may be especially relevant in B cell-mediated diseases, such as systemic lupus erythematosus (SLE). SLE is an extremely heterogeneous, autoimmune disease characterized in part by high titers of autoantibodies. We hypothesize SLE Tregs are deficient in their ability to suppress immunoglobulin secretion by B cells relative to Tregs isolated from healthy donors. We addressed this hypothesis by first developing and characterizing a modified suppression assay in which the only variable is the source of Tregs. In this assay, suppression by human Tregs of a homogenous, germinal center like B cell cell line, Ramos, is measured by ELISA for IgM and flow cytometry for cell death. We demonstrate that human Tregs directly suppress IgM by Ramos B cells through a partially contact- and death-independent mechanism. In addition, we demonstrate that pre-stimulation of the Tregs with αCD3/CD28 increases the suppression of IgM secretion but again, is independent of inducing B cell death. After development and characterization of this modified suppression assay, we evaluated the behavior of Tregs isolated from SLE patients in the assay. Interestingly, we found that the average suppression of IgM secretion by SLE Tregs is not statistically different from the average suppression by Tregs isolated from healthy donors. However, we found that SLE Tregs induce death in the Ramos B cells unlike Tregs isolated from healthy donors. Based on our findings, we offer a model by which Treg-induced B cell death might actually promote more SLE disease by further release of auto-antigens. Future experiments will be aimed at elucidating the mechanism and type of cell death.
The role of STAT6 modulation of natural and inducible Tregs during Allergic Lung InflammationIL-4 plays a central role in allergic responses by activating the STAT6 pathway. Several studies indicate that regulatory T-cells (Treg) are modulated by IL-4 in vitro. We previously showed that STAT6-/- mice are highly resistant to allergic lung inflammation even when wild type Th2 effectors were provided and that they have increased numbers of Tregs. However, the role of STAT6 in modulating Tregs in vivo during allergic lung inflammation has not been thoroughly investigated. We hypothesized that IL-4-induced activation of STAT6 suppresses natural and inducible Treg differentiation, leading to enhanced allergic lung inflammation. Using a GFP marker for Tregs, we found that STAT6-/- mice have increased frequencies and total numbers of natural (n) Tregs in vivo and also increased frequencies of in vitro generated iTregs compared to STAT6-sufficient mice. Additionally, utilization of Helios and Nrp1 as markers for nTregs revealed a similar result. Taken together, these results suggest that STAT6-/- mice are highly resistant to Th2-driven inflammation because of their elevated numbers of Tregs. To test this hypothesis, STAT6-/-, STAT6xRAG2-/- and RAG2-/- mice were subjected to OVA-sensitization and challenge following adoptive transfer of OVA-specific, wild type Th2 effectors with or without prior Treg depletion/ inactivation using anti-CD25 (PC61). As expected, STAT6-/- mice were highly resistant to airway inflammation and remodeling. In contrast, allergic lung inflammation was partially restored in STAT6-/- mice treated with PC61 to levels observed in STAT6xRAG2-/- mice. In some cases, STAT6xRAG2-/- mice were also given nTregs along with Th2 effectors. Adoptive transfer of nTregs caused a substantial reduction in BAL eosinophil composition and suppressed airway remodeling and T-cell migration into the lung in STAT6xRAG2-/- mice to levels comparable to those in STAT6-/- mice. We also analyzed the contribution of another IL-4-activated signaling mediator, insulin receptor substrate 2 (IRS2). In contrast to STAT6, IRS2 suppressed iTreg expansion, but not nTreg expansion in vivo. These results illustrate that two signaling pathways activated by IL-4, STAT6 and IRS2, differentially antagonize Tregs in vivo. STAT6 and IRS2 both suppress iTregs, while only STAT6 suppresses nTregs. Furthermore, we demonstrate that STAT6 suppresses Tregs in vivo thereby promoting allergic airway inflammation.