Bioassay detects soluble MAdCAM‐1 in body fluids

Mucosal addressin cell adhesion molecule (MAdCAM‐1) is a key player in mediating the infiltration of leucocytes into chronically inflamed tissues. Five anti‐MAdCAM‐1 monoclonal antibodies (mAb), designated 17F5, 201F7, 314G8, 377D10 and 355G8, were generated by fusion of P3 × 63Ag8.653 myeloma cells with spleen cells from BALB/c mice immunized with recombinant human MAdCAM‐1‐Fc. The latter four mAb recognize the ligand‐binding first Ig domain, and block T ‐cell adhesion to MAdCAM‐1. The non‐blocking mAb 17F5 recognizes the mucin domain. Extensive analysis of a large panel of paraffin‐embedded human tissues revealed that the 314G8 mAb detected MAdCAM‐1 on venules in the spleen and small intestine. MAdCAM‐1 was strongly expressed in the synovium of osteoarthritis patients, predominantly on the endothelial lining of blood vessels, but also within the vessel lumen. An ELISA, based on mAb 377D10 and 355G8, was developed to determine whether soluble MAdCAM‐1 was present in body fluids, and to measure the levels present. The assay detected soluble MAdCAM‐1 in the serum and urine of healthy donors, at levels similar to those of soluble forms of the related CAM, ICAM‐1 and VCAM‐1. The anti‐MAdCAM‐1 antibodies and assay developed here may be useful therapeutically in the treatment of inflammation in humans. Similarly, they may be useful diagnostically to monitor the presence and levels of MAdCAM‐1.