Detection of soluble α1 integrin in human serum

An enzyme-linked immunosorbent assay (ELISA) for the detection and quantitation of soluble alpha 1 beta 1 integrins (s alpha 1) in human serum samples was developed. Solid phase-bound anti-al integrin monoclonal antibody (mAb) TS2/7 was used to capture sal,and mAb 1B3.1 was used to detect the immobilized integrin. An extract of human placenta (PE) containing 340 ng/mL of VLA-1 molecules served as a positive control, and serum samples from normal donors and patients were assayed. Optimal binding of anti-al integrin mAb 1B3.1,expressed as specific optical density (OD), was obtained when a 5 mu g/mL solution of anti-at integrin "capture" mAb TS2/7 was immobilized to the wells and the PE was added. Solutions of albumin or collagen, in contrast, did not result in binding, confirming the specificity of the assay for sat. Furthermore, the specific OD of the wells correlated directly with the concentration of PE. A concentration of sat above that of a 1:100 dilution of PE--that is, >3.4 ng/mL of integrin, in which the intra-assay correlation of variance was <5.7%, was found in 5 of 8, 3 of 8, and 6 of 9 serum samples from normal individuals, patients with connective tissue diseases (CTD), and patients with liver diseases (LD), respectively. These results suggest, for the first time, that sat are present in healthy and diseased human serum.