Background/Purpose: Recent studies have revealed that platelets play pivotal roles in inflammation in addition to hemostasis. The thrombus induces subsequent local inflammation and reversely the local inflammation results in the formation of thrombus. Therefore, to suppress activation of platelets is important for preventing tissue damages. In this study, we aim to reveal effects of activated platelets on IL-1b production in human PBMCs and to clarify the mechanism.

Methods: We investigated whether IL-1b production is enhanced by co-culture of PBMCs and platelets compared to PBMCs alone. We analyzed the production of IL-1 b in co-culture of each fraction of PBMCs, T cells, B cells, NK cells and monocytes with platelets. NLRP3, or caspase-1 was knocked down by shRNA in THP-1 monocytes, and IL-1b production induced by co-culture with platelets were compared among shRNA-cell lines and scramble controls. We investigated mediators derived from platelets that induced IL-1 b production from monocytes, using inhibitors and neutralization antibodies. Furthermore, we compared CD16 positive monocytes with CD16 negative monocytes, regarding IL-1b productivities, expression levels of NLRP3 and caspase-1 mRNA, and platelets-monocytes-aggregates (PMA) ratios. Activation of platelets in inflammatory diseases, rheumatoid arthritis (RA) and Behcet’s disease (BD) were analyzed using CD62P and PMA ratio.

Results: IL-1b production was enhanced by co-culture of PBMCs with platelets compared to PBMCs alone. Among PBMCs, monocytes showed the most prominent IL-1b production by co-culture with platelets. NLRP3- and caspase-1-knockdown THP-1 cells showed significantly lower IL-1b production in co-culture with platelets than scramble controls. CCR5 inhibitor and ATP inhibitor significantly attenuated IL-1b production of monocytes co-cultured with platelets. CD16-positive monocytes produced more IL-1b in co-culture with platelets than CD16-negative monocytes. CD16-positive monocytes showed higher NLRP3 mRNA expression and higher PMA ratio than CD16-negative monocytes. Platelets were activated in patients with active RA and BD compared to health controls.

Conclusion: Platelets stimulate monocytes and have the ability to enhance IL-1b production via CCL 5 and ATP. They activate NF-kB pathway and NLRP3 inflammasomes in monocytes and enhance IL-1b production. Among monocytes, CD16-positive monocytes are highly bound to platelets and produce IL-1b. Activated platelet may be involved in disease progression of inflammatory diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/platelets-induce-il-1b-production-in-human-monocytes-through-nlrp3-inflammasome-activation/