Involvement of monocyte/macrophage NLRP3-IL-1β signaling in the pathogenesis of myasthenia gravis.

BACKGROUND: Myasthenia gravis is an autoimmune disorder mediated by pathogenic autoantibodies targeting the neuromuscular junction. Although the role of adaptive immunity is well-established, the involvement of innate immune cells, particularly monocytes and macrophages, in myasthenia gravis pathogenesis remains unclear. This study investigated whether the NLRP3 inflammasome-caspase-1-IL-1β pathway in monocytes and macrophages contributes to disease development in myasthenia gravis and its experimental model.

METHODS: Experimental autoimmune myasthenia gravis was induced in Lewis rats by immunization with AChR97-116 peptide. Splenic and lymph node CD11b/c+ macrophages were analyzed by flow cytometry at early (d14), middle (d30), and late (d46) disease stages. Bulk RNA sequencing was performed on sorted splenic CD11b/c+ macrophages from experimental autoimmune myasthenia gravis and control rats at d14. Peripheral blood mononuclear cells were collected from myasthenia gravis patients during clinical exacerbation (n = 36) and healthy controls (n = 35). Monocyte subsets and intracellular caspase-1/IL-1β expression were assessed by flow cytometry. Correlations with clinical severity (QMG score) and lymphocyte counts were analyzed.

RESULTS: In EAMG rats, the proportion of CD11b/c+ macrophages increased significantly in the spleen and lymph nodes during early and middle disease stages. These macrophages showed elevated expression of Nlrp3, Casp1, and Il1b, with enrichment of the NOD-like receptor signaling pathway. The frequencies of CD11b/c+caspase-1+ and CD11b/c+IL-1β+ macrophages were significantly higher in early and middle stages compared to controls and late stage. In myasthenia gravis patients, the proportion of CD14+ monocytes were increased during clinical exacerbation, with expansion of both classical (CD14++CD16-) and intermediate (CD14++CD16+) subsets. Classical monocytes exhibited elevated IL-1β expression, while intermediate monocytes showed increased caspase-1 expression. The frequency of CD14+ monocytes, CD14+caspase-1+ monocytes and IL-1β expression in intermediate monocytes positively correlated with QMG scores. Moreover, IL-1β+ classical and intermediate monocyte frequencies correlated with CD4+ T cell counts.

CONCLUSION: Monocytes and macrophages contribute to myasthenia gravis pathogenesis through activation of the NLRP3-caspase-1-IL-1β pathway, particularly during early disease stages. This innate immune activation promotes T cell expansion and correlates with disease severity, suggesting that targeting this pathway may represent a potential therapeutic strategy for myasthenia gravis.