The Vitronectin Receptor and its Associated CD47 Molecule Mediates Proinflammatory Cytokine Synthesis in Human Monocytes by Interaction with Soluble CD23

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Abstract
The vitronectin receptor, αvβ3 integrin, plays an important role in tumor cell invasion, angiogenesis, and phagocytosis of apoptotic cells. CD47, a member of the multispan transmembrane receptor family, physically and functionally associates with vitronectin receptor (VnR). Although vitronectin (Vn) is not a ligand of CD47, anti-CD47 and β3 mAbs suppress Vn, but not fibronectin (Fn) binding and function. Here, we show that anti-CD47, anti-β3 mAb and Vn, but not Fn, inhibit sCD23-mediated proinflammatory function (TNF-α, IL-12, and IFN-γ release). Surprisingly, anti-CD47 and β3 mAbs do not block sCD23 binding to αv+β3+ T cell lines, whereas Vn and an αv mAb (clone AMF7) do inhibit sCD23 binding, suggesting the VnR complex may be a functional receptor for sCD23. sCD23 directly binds αv+β3+/CD47− cell lines, but coexpression of CD47 increases binding. Moreover, sCD23 binds purified αv protein and a single human αv chain CHO transfectant. We conclude that the VnR and its associated CD47 molecule may function as a novel receptor for sCD23 to mediate its proinflammatory activity and, as such, may be involved in the inflammatory process of the immune response.