Session Type: Abstract Submissions (ACR)
Systemic sclerosis (SSc) is a multi-organ fibrotic disease associated with auto-immune abnormalities. Several clinical and experimental observations suggest that B cells are involved in the inflammatory and fibrotic processes responsible for the disease; but their exact role has yet to be precisely explored. In this work, we assessed the B cell homeostasis modifications in a murine model of SSc (HOCl mouse), both at a phenotypic and functional level, during the course of the disease.
Overall, 48 Balb/c mice underwent daily subcutaneous injection of hypochlorous acid (HOCl) or PBS, and were then sacrificed at day 21 (early, inflammatory stage) or day 42 (late, fibrotic stage) from the beginning of the protocol (n=12 in each of the 4 groups). Mouse spleens were retrieved and immediately dissected. The distribution of the splenic leucocyte populations (B cells, T CD4 and CD8 cells, macrophages) and B cell subsets (transitionnal, follicular, marginal zone, B1 and regulatory B cells) was analyzed by flow cytometry. The functional properties of B cells were evaluated by MACS- or FACS-sorting the different subsets, and measuring the secretion levels of 20 cytokines in culture supernatants, after stimulation by LPS and CD40L for 48h.
The phenotypic analysis showed a B cell expansion in the HOCl mice at both stages of the disease. This expansion concerns mainly the transitional and B1a cells at the early stage; and mostly the mature forms (follicular and marginal zone) and B1b cells at the later stage. The regulatory CD5+ CD1dhi B cells were also shown to expand at both times of the disease, but more importantly during the inflammatory stage.
At a functional level, the large screening of B cell secretion capacities identified 2 cytokines that were differently produced within the 4 groups: IL-6 and MIP-1α. Those 2 cytokines, that display pro-inflammatory and pro-fibrotic properties, were produced in more important levels in the supernatant of B cells culture from HOCl mice, at both stages of the disease. Within the B cell compartment, IL-6 was mainly secreted by the marginal zone (MZ) subset. Due to its potential regulatory effects, a special focus was also given on IL-10 secretion. Levels of IL-10 in the supernatant of B cells appeared similar in the 4 groups.
To our knowledge, this study is the first to find evidence of B cell homeostasis alterations in murine model of SSc. It further implies a potential implication of B cells in the pathogenesis of this disease, either by secretion of cytokines (like IL-6 and MIP-1α) or by expansion of pathogenic subsets (such as marginal zone B cells). The exact role of the regulatory B cell subset, that may exert beneficial properties, needs further studying, as the expansion of the CD5+ CD1dhi B cells in HOCl mice seems inconsistent with the similar secretion of IL-10 in the 4 groups. Nevertheless, in light of those results, the B cell appears to be a relevant target for therapy in SSc.
This research work was supported by a grant from Association des Sclérodermiques de France.
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