Direct Suppression by Healthy and SLE Human Tregs of B cell Immunoglobulin Secretion
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AbstractRegulatory 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.
DescriptionUniversity of Maryland, Baltimore. Molecular Microbiology and Immunology. Ph.D. 2017
regulatory T cells
Lupus Erythematosus, Systemic