IL-40: A New B Cell-Associated Cytokine Up-Regulated in Rheumatoid Arthritis Decreases Following the Rituximab Therapy and Correlates With Disease Activity, Autoantibodies, and NETosis

Abstract

BackgroundInterleukin 40 (IL-40) is a newly identified B cell-associated cytokine implicated in humoral immune responses and B cell homeostasis. As B cells play a pivotal role in autoimmunity, we investigated the function of IL-40 in rheumatoid arthritis (RA).MethodsIL-40 expression was determined in the synovial tissue from RA and osteoarthritis (OA) patients. IL-40 was analysed in the serum/synovial fluid of patients with RA (n=50), systemic lupus erythematosus (SLE, n=69), OA (n=44), and healthy controls (HC, n=50). We assessed the changes of IL-40 levels in RA patients following the B cell depletion by rituximab (n=29) or after the TNF inhibition by adalimumab (n=25). We examined the relationship between IL-40, disease activity, autoantibodies, cytokines, and NETosis markers. Effect of IL-40 on synovial fibroblasts was determined.ResultsIL-40 was overexpressed in RA synovial tissue, particularly by synovial lining and infiltrating immune cells. The levels of IL-40 were up-regulated in the synovial fluid of RA versus OA patients (p<0.0001). Similarly, IL-40 was increased in the serum of RA patients compared to HC, OA, or SLE (p<0.0001 for all) and decreased after 16 and 24 weeks (p<0.01 and p<0.01) following rituximab treatment. No significant effect of adalimumab on IL-40 was observed. IL-40 levels in RA patients correlated with rheumatoid factor-IgM and anti-cyclic citrullinated peptides (anti-CCP) in the serum (p<0.0001 and p<0.01), as well as in the synovial fluid (p<0.0001 and p<0.001). Synovial fluid IL-40 was also associated with disease activity score DAS28 (p<0.05), synovial fluid leukocyte count (p<0.01), neutrophil attractants IL-8 (p<0.01), MIP-1α (p<0.01), and markers of neutrophil extracellular traps externalization (NETosis) such as proteinase 3 (p<0.0001) and neutrophil elastase (p<0.0001). Synovial fibroblasts exposed to IL-40 increased the secretion of IL-8 (p<0.01), MCP-1 (p<0.05), and MMP-13 (p<0.01) compared to the unstimulated cells.ConclusionsWe show the up-regulation of IL-40 in RA and its decrease following B cell depleting therapy. The association of IL-40 with autoantibodies, chemokines, and markers of NETosis may imply its potential involvement in RA development. Moreover, IL-40 up-regulates the secretion of chemokines and MMP-13 in synovial fibroblasts, indicating its role in the regulation of inflammation and tissue destruction in RA.

Possible role for IL-40 and IL-40-producing cells in the lymphocytic infiltrated salivary glands of patients with primary Sjögren’s syndrome

“… 23 Recently, IL-40 was found upregulated in RA, suggesting a role for this molecule in B-cell driven rheumatic diseases. 24 As found in RA synovium, IL-40 was strongly upregulated in pSS among lymphocytic infiltrates and ductal epithelial cells and significantly correlated with the FS. Specifically, epithelial cells are thought to play an important pathogenetic role in pSS, as suggested by the demonstration that, in the histopathological lesions of patients with pSS, ductal and acinar salivary gland epithelial cells display high levels of several immunoactive molecules that are known to mediate the lymphoid cell homing, antigen presentation and the amplification of epithelial cell–immune cell interactions.…”

“…The first link to autoimmune disease dates back to 2012 when the presence of C17orf99 gene was described as a marker of autoimmune hepatitis 23. Recently, IL-40 was found upregulated in RA, suggesting a role for this molecule in B-cell driven rheumatic diseases 24. As found in RA synovium, IL-40 was strongly upregulated in pSS among lymphocytic infiltrates and ductal epithelial cells and significantly correlated with the FS.…”

“…In addition to B and T cells, a further important role of IL-40 could be related to the modulation of neutrophil function within the SG of pSS. In fact, IL-40 was already related to NETosis enhancement in RA24 but, up to date, despite an increase in neutrophils frequency was depicted in pSS, a complete assessment of neutrophils functions is not available 26. The presence of both non-lytic and lytic NETosis was previously described in systemic lupus erythematosus, a systemic disease that shares common pathways with pSS 27.…”

New pro-inflammatory cytokine IL-40 is produced by activated neutrophils and plays a role in the early stages of seropositive rheumatoid arthritis

“… 10 Very recently, an upregulation of IL-40 in RA was demonstrated. 11 12 Based on our study on RA, 11 the elevation of IL-40 in RA is associated with disease activity, autoantibodies and the externalisation of neutrophil extracellular traps (NETosis). We also demonstrated that elevated serum levels of IL-40 significantly decreased following B-cell depletion therapy (rituximab) in RA patients.…”

“…According to our in vitro studies, IL-40 acts as an inducer of chemokines, and metalloproteinase release by RA synovial fibroblasts. 11 …”