Integrin Crosstalk Regulation of Human Neutrophils Adhered to Fibronectin and Beta‐glucan

Complement Receptor 3 (CR3), an integrin found on neutrophils, plays an important role in fungal recognition. Co‐ligation of CR3 with fibronectin (Fn) at the I‐domain and β‐glucan (B) at the lectin‐like domain is possible due to spatially distinct locations. Dual ligation of CR3 with Fn+B induces homotypic aggregation of primed neutrophils, a response representative of the immune cells encounter with fungi within tissues, and can be blocked by anti‐CR3 antibody. Previous findings have shown that CR3‐mediated DNA Neutrophillic Extracellular Traps (NETS) coincide with PMN aggregates. To understand the molecular mechanisms of how CR3 coordinates these neutrophil responses, we explored the role of the integrins CR3, VLA3, and VLA5. Using antibody blockade and receptor‐FRET, we unexpectedly discovered a required CR3‐mediated role for VLA3, the canonical laminin receptor, in aggregate formation. The role of VLA3 was specific as blockade of other β1 integrin family members failed to prevent aggregation including VLA5, the canonical Fn receptor. Exploring the role of VLA5 using an activating anti‐VLA5 antibody, we showed active inhibition of VLA5 is necessary for aggregate formation. In assessing NETs formation, we discovered that unlike aggregate formation, VLA5 and CR3 are necessary for NET formation, where VLA3 is not. These results have identified a novel integrin crosstalk pathway in which CR3 serves as a master regulator of VLA3 and VLA5 in response to fungal infections and increased our understanding of the complex regulation of integrins. NIH GM‐066194