Trichinella spiralis serine proteinase enhances antibody-dependent cell-mediated (ADCC) killing of newborn larvae by driving M1 polarization via the NF-κB pathway.

Previous studies have shown that recombinant Trichinella spiralis serine proteinase (rTsSPc) promoted larval invasion of the gut epithelium, but its regulatory role on macrophage polarization is not clear. Immunofluorescence assay (IFA) confirmed specific rTsSPc's binding to RAW264.7 macrophages. The results of qPCR, Western blot, ELISA, and flow cytometry showed that rTsSPc significantly upregulated M1 macrophage markers (iNOS and CD86) and pro-inflammatory cytokines (TNF-α and IL-6), but not M2 markers (Arg1, CD206) and anti-inflammatory cytokines (IL-10, TGF-β). However, intestinal infective larvae (IIL) excretory-secretory antigens (ESAs) induced M2 polarization. Western blot revealed that rTsSPc activated the classical NF-κB pathway, as evidenced by increased phosphorylation levels of IKKβ, IκB-α, and NF-κB p65. Pretreatment of macrophages with NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) effectively suppressed rTsSPc-induced M1 polarization, decreased pro-inflammatory cytokine secretion, and reduced nitric oxide (NO) production. Functionally, rTsSPc-induced M1 polarization significantly enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) of macrophages killing newborn larvae, but PDTC pretreatment resulted in a 41.62% reduction in cytotoxicity. Our results showed that rTsSPc bound specifically to macrophages and induced M1 polarization by activating the classical NF-κB pathway, thereby enhancing macrophage-mediated ADCC killing of newborn larvae. The findings indicated that TsSPc might strengthen host protective immunity via ADCC killing of larvae, and TsSPc may be considered a potential candidate antigen for developing anti-Trichinella vaccines.