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.

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A novel experimental model was established in normal rats for studying the localisation and tissue distribution of a murine monoclonal antibody directed against kappa light chain B cell malignancies. The antibody, K-1-21 was raised against human kappa Bence Jones Proteins and reacts with a cell membrane antigen KMA which is restricted to some kappa myeloma and lymphoma cells. In the rat model, kappa or lambda Bence Jones protein-conjugated sepharose was implanted subcutaneously on either flank 24 h before the injection of 131I-labelled K-1-21 or its F(ab')2 fragment. Gamma camera imaging and tissue distribution studies showed specific localisation of the K-1-21 antibody in the kappa sepharose. Injection of F(ab')2 antibody fragments resulted in faster background clearance, earlier delineation of the specific image and significantly higher target to blood ratios than those obtained with the intact antibody. These results suggest that the model may provide an alternative system to tumour xenograft bearing nude mice for studying localisation of antibodies with therapeutic potential.