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α4β7 Integrin Mediates B Cell Binding to Fibronectin and Vascular Cell Adhesion Molecule-1: Expression and Function of α4 Integrins on Human B Lymphocytes

Abstract:

Cell-cell and cell-extracellular matrix interactions are mediated by a wide array of cell surface molecules known as adhesion receptors, including the integrin family that comprises numerous αβ heterodimers. A new integrin group, the β7 subfamily, has been recently defined. Its two members, α4β7 and α<inf>H</inf>β7, are involved in the lymphocyte migration to the Peyer's patches and the intestinal mucosa, respectively. We have analyzed the expression of α4β7 integrin on B cells from different cellular compartments and at different activation states. Resting peripheral blood B lymphocytes constitutively express large amounts of α4β7. By contrast, α4β7 integrin, which is absent on resident B cells from different lymphoid tissues, is induced upon activation. Functional studies indicates that α4β7 is mediating B cell attachment to fibronectin and vascular cell adhesion molecule-1 through distinct epitopes on this integrin. Furthermore, the α4β7 integrin is also implicated in intercellular interactions as deduced by the ability of anti-α4β7 mAb to trigger homotypic B cell aggregation. Finally, α4β7 and α4β1 integrins redistribute at the cell membrane in a similar clustering pattern when B cells attach to fibronectin- and vascular cell adhesion molecule-1-coated surfaces. Our studies demonstrate the differential regulation on the expression and function of α4β7 integrin among different human B cell populations.