Analysis of adhesion molecules on mast cells

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Adhesion molecules of the integrin family are implicated not only in leukocyte migration but also in leukocyte activation. Here we characterize the expression and function of fibronectin receptor integrins on rat mast cells. A rat basophilic leukemia cell line (RBL-2H3) and phorbol ester-stimulated rat peritoneal mast cells adhered to fibronectin (FN), vitronectin and fibrinogen. These mast cells expressed fibronectin receptor integrins, including very late antigen (VLA)-4, VLA-5 and virtonectin receptor (VNR), as estimated by immunofluorescent staining and inhibition of FN adherence by newly established mAbs reactive with the rat alpha4 (MRalpha4-1), alpha5 (HMalpha5-1) or beta3 (HMbeta3-1) chains of the integrin molecules. The beta-hexosaminidase release, a marker for mast cell degranulation, triggered by high affinity IgE receptor (FcepsilonRI) -mediated stimulation, was enhanced by adhesion of RBL-2H3 cells to either immunobilized FN,MRalpha4-1, HMalpha5-1, or HMbeta3-1. This FN enhancement of beta-hexosaminidase release was inhibited by soluble MRalpha4-1, H M alpha5-1, and HMbeta3-1 as well as by GRGDSP and DELPQLVTLPHPNHLGPEILDVPST peptides which abrogate VLA-5/VNR and VLA-4 binding to FN respectively. In vivo, passive cutaneous anaphylaxis induced by IgE anti-DNP and DNP-BSA was inhibited by concurrent s.c. injection of MRalpha4-1, HMalpha5-1, and HMbeta3-1. These results demonstrate that FN receptor integrins expressed on rat mast cells play an important role in regulating mast cell activation both in vitro and in in vivo.