ECRG4 mediates host response to cutaneous infection by regulating neutrophil recruitment and adhesion receptor expression.

Rapid neutrophil recruitment is critical for controlling infection, with dysfunctional neutrophil responses in diseases like diabetes associated with greater morbidity and mortality. We have shown that the leukocyte protein ECRG4 enhances early neutrophil recruitment to cutaneous wounds and hypothesized that ECRG4 regulates the early host response to infection. Using a cutaneous infection model, we found that ECRG4 KO mice had decreased early neutrophil recruitment with persistent larger lesions, increased bacterial proliferation and systemic dissemination. Although previous work identified ECRG4 as a negative regulator of CD44 on neutrophils, the mechanism regulating neutrophil recruitment remained unknown. We demonstrated that pro-inflammatory responses were intact in ECRG4 KO mice, but found decreased neutrophil mobilization from bone marrow and decreased migration to chemokines. ECRG4 KO mouse neutrophils demonstrated an increase in adhesion molecules that regulate recruitment, including enhanced induction of integrin CD11b and increased L-selectin and CD44 on bone marrow neutrophils. Analysis of gene expression in leukocytes from diabetic patients found decreased ECRG4 expression with similar increased L-selectin and CD44. We propose a previously unrecognized mechanism governing neutrophil recruitment, whereby ECRG4 mediates neutrophil surface adhesion molecules that determine both recruitment and outside-in signaling that modulates neutrophil response to pro-inflammatory stimuli.