The MRα4-1 antibody reacts with the integrin α4 chain, which is expressed as a heterodimer with either of two β chains, β1 or β7. The α4β1 integrin (VLA-4, CD49d/CD29) is expressed on peripheral T and B lymphocytes, thymocytes, and monocytes; while the α4β7 integrin (LPAM-1) is expressed on peripheral lymphocytes. These integrins mediate a variety of cell-cell and cell-matrix interactions, recognizing the ligands CD106 (VCAM-1), MAdCAM-1, and fibronectin. It has been reported that soluble mAb MRα4-1 partially inhibits in vitro binding of VCAM-1 and mast cells to fibronectin and inhibits the enhanced degranulation of IgE-sensitized RBL-2H3 basophilic leukemia cell line induced on fibronectin-coated plates. Furthermore, plate-bound MRα4-1 antibody enhances the degranulation of IgE-sensitized RBL-2H3 cells; and subcutaneous injection of MRα4-1 mAb, along with anti-CD49e and anti-CD61 antibodies, inhibits experimentally induced passive cutaneous anaphylaxis.