ABSTRACT While NLRP3 has been extensively studied in myeloid cells, its existence and regulation in epithelial cells, including keratinocytes, are unclear. In fact, whether human keratinocytes express a functional NLRP3 inflammasome at all remains a matter of debate in the inflammasome field. Here, we provide additional evidence that NLRP3 is repressed in human keratinocytes cultured under non-inflammatory conditions but can be sharply induced by interferon-γ (IFNγ)—but not lipopolysaccharide (LPS). In this IFNγ-primed state, not all established NLRP3 activators are specific to NLRP3. We report that nigericin-driven keratinocyte pyroptosis occurs via both NLRP1 and NLRP3, whereas Staphylococcus aureus α-hemolysin (Hla) exclusively and nonredundantly activates NLRP3, even though both require K+ efflux. Furthermore, in the presence of T cells, certain virulent S. aureus strains can cause NLRP3-dependent pyroptotic death in keratinocytes in vitro through the cooperative actions of superantigens (SAgs) and Hla. In summary, our findings establish the strict inducibility and functional relevance of the NLRP3 inflammasome in non-myeloid, epithelial cells in vitro. These results resolve conflicting reports and position keratinocytes as a context-specific, non-hematopoietic cellular model for studying NLRP3 activation in host-microbe interactions at barrier tissues. KEY FINDINGS Additional evidence that NLRP3 is absent in resting, nonstimulated human keratinocytes in vitro IFNγ, but not LPS, is a potent ‘priming’ signal for NLRP3 in human keratinocytes in vitro In IFNγ-primed keratinocytes, S. aureus α-hemolysin (Hla) selectively activates NLRP3, whereas nigericin activates both NLRP1 and NLRP3 in vitro SAg and Hla kill keratinocytes via NLRP3-driven pyroptosis in the presence of T cells in vitro GRAPHICAL ABSTRACT
Rozario et al. (Sat,) studied this question.