Monoclonal antibody based ELISAs for measurement of activins in biological fluids

Two sensitive monoclonal antibody (MAb)-based enzyme-linked immunosorbent assays (ELISAs), one for activin A (homodimer of β_A subunits) and one for activin B (homodimer of β_B subunits) in plasma have been developed. The activin A ELISA had an effective range of 0.2-50 ng/ml while the activin B ELISA's range was 0.1-25 ng/ml in human serum. Both ELISAs were specific with <0.01% cross-reactivity with related hormones and follistatin (an activin binding protein), however the presence of recombinant human follistatin caused a decrease in measured level of activin A and B spiked human samples. The assay was linear across the standard curve range with intra- and interassay coefficients of variation were less than 15%. The level of activins in female serum range from 0.3 to 10.4 ng/ml. In summary, we have developed a reliable, convenient and rapid MAb-based enzyme immunoassay for determination of activin A and B levels in human serum which are also applicable for buffer, mouse and monkey serum matrices. This assay will be useful for studying the regulation and role of activin A and B in health and disease.