The Sarcoptes scabiei Kazal-type inhibitor SsKaSPI exhibits elastase-inhibitory activity and modulates neutrophil extracellular trap formation.

Scabies, caused by the ectoparasitic mite Sarcoptes scabiei, is a contagious zoonotic disease that poses a significant global health burden. The emergence of drug resistance and the lack of effective vaccines underscore the urgent need for novel molecular targets. In this study, we characterized a novel Kazal-type serine protease inhibitor from S. scabiei (SsKaSPI). Immunofluorescence assays localized native SsKaSPI within the mite body and throughout the infested host skin, suggesting that SsKaSPI may be released into host tissues and act at the host-parasite interface. In an in vitro PMA-induced NETosis model using murine bone marrow neutrophils, recombinant SsKaSPI (rSsKaSPI) significantly reduced NET formation without inducing detectable cytotoxicity. Mechanistically, molecular docking predicted a potential interaction between SsKaSPI and elastase, while an in vitro enzymatic assay showed that rSsKaSPI moderately inhibited porcine pancreatic elastase activity. These findings suggest a possible elastase-associated mechanism underlying the suppression of NETosis, although direct inhibition of host neutrophil elastase remains to be further validated. Furthermore, transcriptomic profiling showed that rSsKaSPI altered inflammatory gene expression in neutrophils, with enrichment of IL-17 and TNF signaling pathways. This transcriptional response was accompanied by decreased IL-1β mRNA expression and increased IL-10 mRNA expression. Together, these findings suggest that SsKaSPI may contribute to S. scabiei immune evasion by modulating NET formation and host inflammatory gene expression, although its role under natural infestation conditions remains to be fully investigated. Our results highlight SsKaSPI as a potential molecular target for future anti-scabies studies.