Interleukin-36 receptor mediates the crosstalk between plasma cells and synovial fibroblasts.

The IL-1 family member IL-36 alpha has proinflammatory and pathogenic properties in psoriasis. IL-36 alpha binds to the IL-36 receptor leading to nuclear factor kappa B/mitogen activated protein kinase mediated cytokine release. The IL-36R antagonist prevents recruitment of IL-1 receptor accessory protein and therefore IL-36-dependent cell activation. In inflamed human tissue, we previously could show that resident B cells and plasma cells (PC) express IL-36 alpha. Further, fibroblast-like synoviocytes (FLS) produced proinflammatory cytokines upon IL-36 alpha-stimulation. We hypothesize an IL-36-specific crosstalk between B cells/PCs and FLS permitting a proinflammatory B cell niche. Here, we firstly demonstrated that B cell lines and B cells from healthy donors express IL-36 alpha and stimulation increased IL-36 alpha in B cells and primary plasmablasts/PCs. Moreover, FLS respond specifically to IL-36 alpha by proliferation and production of matrix metalloproteinases via p38/HSP27 signaling. Importantly, IL-36R-deficiency abrogated IL-36 alpha-induced production of inflammatory mediators in FLS and changed the intrinsic FLS-phenotype. Using an in vitro co-culture system, we could show that IL-36R-deficient FLS had a limited capacity to support PC survival compared to wild-type FLS. Hence, we demonstrated an IL-36R-dependent crosstalk between B cells/PCs and FLS. Our data support the concept of initiation and maintenance of a proinflammatory niche by B cells in the joints.