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. 2010 Mar 1;78(5):1884–1894. doi: 10.1128/IAI.01143-09

FIG. 8.

FIG. 8.

Proposed model of IL-1α secretion in L. monocytogenes-infected macrophages. Upon L. monocytogenes infection, activation of the TLR/MyD88 signaling pathway induces IL-1α mRNA expression and pro-IL-1α synthesis independently of bacterial entry into the cytoplasm. LLO-induced cytoplasmic entry of bacteria is essential for secretion of mature IL-1α without any involvement of inflammasome activation. Entry of L. monocytogenes into the host cytoplasm leads to an elevation in the intracellular calcium level and activation of calpain protease, involved in the processing and secretion of mature IL-1α.