An enzyme-linked immunosorbent assay (ELISA) for the detection and quantitation of soluble α1β1 integrins (sα1) in human serum samples was developed. Solid phase-bound anti-α1 integrin monoclonal antibody (mAb) TS2/7 was used to capture sα1, 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-α1 integrin mAb 1B3.1, expressed as specific optical density (OD), was obtained when a 5 μg/mL solution of anti-α1 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 sα1. Furthermore, the specific OD of the wells correlated directly with the concentration of PE. A concentration of sα1 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 sα1 are present in healthy and diseased human serum.
Bank, I., Weiss, P., Doolman, R., Book, M., & Sela, B. A. (1999). Detection of soluble integrin in human serum. Journal of Laboratory and Clinical Medicine, 134(6), 599–604. https://doi.org/10.1016/S0022-2143(99)90099-9