RPSA-OLFM4 axis governs neutrophil migration against bacterial infection and sepsis.

Neutrophil migration to bacterial infection sites is key for host defense. Host ribosomal protein SA (RPSA) has been recently reported to regulate the anti-infection immunity of immune cells; however, its role in neutrophil migration remains unclear. Here, using myeloid-specific Rpsa-deficient mice, we found that RPSA deletion inhibited neutrophil infiltration and markedly exacerbated Streptococcus suis serotype 2 infection. Adoptive cell transfer and neutrophil depletion assays identified RPSA as vital for the anti-infective function of neutrophils. Mechanistically, RPSA deficiency induced the overexpression of olfactomedin 4 (OLFM4), which in turn inhibited the activation of the RhoA/ROCK1/pMLC2 signaling pathway, reduced MYH9 expression, and caused aberrant MYH9 translocation from the uropod to the cytosol in migrating neutrophils. Ultimately, this disrupted cytoskeletal polarization and uropod extension, thereby abrogating migratory function. Clinically, septic patients' neutrophils exhibited reduced RPSA and elevated OLFM4 expression, a phenotype that correlated with a marked impairment of migratory capacity. Therapeutic targeting of the RPSA-OLFM4 axis restored neutrophil migration and improved disease outcomes in both S. suis 2-infected and septic mice. Thus, our findings demonstrate that RPSA promotes neutrophil migration via downregulating OLFM4 to counter bacterial infection, and establish the RPSA-OLFM4 axis as a critical immune migratory checkpoint in host antibacterial immunity.