Monoclonal antibody against human somatomedin-C/insulin-like growth factor-I.

A monoclonal IgG3 antibody produced by mouse hybridoma shows high specificity for human somatomedin-C (SM-C) and insulin-like growth factor-I (IGF-I). The apparent Ka for SM-C is 1.7 x 10(10) M-1. At 1:2000 final dilution, culture medium from antibody-producing cells binds 35-40% of radioiodinated SM and IGF-I tracers, while similar binding is seen with ascites fluid from tumor-bearing mice at 1:200,000 dilution. Rat SM, multiplication stimulating activity, IGF-I C-peptide and human insulin show little or no crossreactivity, while IGF-II has 7%, and IGF-I 70%, of the potency of SM-C. Of a variety of species tested, acid-ethanol extracted guinea pig serum has the greatest immunoreactivity, and extracts of rabbit, rat and mouse serum have the lowest activity. Human plasma extracts give displacement curves parallel to purified SM, and vary in potency depending upon the GH status of the donor. These results suggest that this antibody will be of value for SM-C/IGF-I radioimmunoassay.