Altered expression of IL-10 family cytokines in CRMO result in enhanced inflammasome activation

Chronic recurrent multifocal osteomyelitis (CRMO) is the most severe presentation of the autoinflammatory bone disorder chronic nonbacterial osteomyelitis (CNO). The pathophysiology of CNO remains to be determined. We recently demonstrated reduced activation of mitogen-activated protein kinases ERK1 and 2 in monocytes from CRMO patients responsible for impaired activation of the transcription factor signaling protein (Sp-)1. This resulted in failure to express the immuno-modulatory cytokine IL-10. The IL10 gene, together with its homologues IL19 and IL20, is organized in the 145 kb spanning IL10 cytokine cluster on chromosome 1q32. In most cells, including monocytes, IL-10 cytokine family members are co-regulated in response to certain stimuli. IL-10 and IL-19 mainly have immune-modulating functions, while IL-20 acts as a pro-inflammatory cytokine contributing to inflammatory bone-loss. The NLRP3 inflammasome is a multi-protein complex forming in response to innate stimuli, subsequently mediating the cleavage and release of IL-1β. Enhanced inflammasome activation in IL-10 deficient mice was linked with bone-loss. Convincing evidence of this mechanism playing a role in CNO, however, is lacking.