Sialylation of CD11b/CD18 regulates Neutrophil Transepithelial Migration and Neutrophil Inflammatory function in the Intestine

Abstract

Neutrophils (PMNs) are the first immune responders to infection/inflammation playing critical roles in clearing invading microbes and promoting tissue repair. However, dysregulated trafficking of PMNs across mucosal surfaces is a pathological hallmark of diseases characterized by persistent or intermittent bursts of inflammation including inflammatory bowel disease (IBD). The critical final step in PMN trafficking into mucosal lined organs (including the gut) involves transepithelial migration (TEpM). The glycoprotein CD11b/CD18 is the predominant β2 integrin mediating PMN TEpM into the intestinal lumen. Furthermore, CD11b/CD18 also regulates key PMN inflammatory effector functions that are implicated in IBD pathogenesis including superoxide release. We have previously demonstrated that specific GlcNAc and Lewis X glycan structures on CD11b/CD18 can be targeted to reduce PMN intestinal trafficking. Recent mass spectrometry analyses revealed the presence of specific sialylated glycan structures on PMN CD11b. However the role of sialylation in regulating PMN CD11b/CD18 function is not well understood. Using lectins recognizing the most common linkages of sialic acid we show that sialidase mediated removal of α2‐3 sialic acid from CD11b/CD18 occurs during PMN migration across intestinal epithelia. Furthermore, specific inhibition of sialidase activity was found to reduce PMN intestinal migration in vitro and in vivo. In addition to limiting PMN intestinal trafficking, sialidase inhibition also reduced key PMN effector functions including degranulation and superoxide release. Finally, we demonstrate that sialidase inhibition impedes PMN CD11b activation and blocks downstream β2 integrin signaling mediated by Spleen tyrosine kinase (Syk). Therefore α2‐3 sialylated glycans on CD11b/CD18 represent novel targets for ameliorating PMN mediated intestinal tissue damage and reducing mucosal inflammation in IBD.