Radioimmunoassay of a human serum growth factor for Balb/c-3T3 cells: derivation from platelets.

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Abstract
A radioimmunoassay was developed for the detection and quantification of a human serum polypeptide that has growth-promoting activity for confluent Balb/c-3T3 [mouse fibroblasts] cells. Antiserum to this growth factor does not recognize antigens in mouse, guinea pig or bovine serum but does detect some crossreacting antigen in the serum of the New World monkey Cebus albifrons and more in the serum of the Old World rhesus monkeys Macaca mulatta and M. fascicularis, demonstrating that the antigenic determinants of the growth factor have a degree of species specificity. Serum derived from whole human blood contains approximately 770 pg of the growth factor per mg of protein; serum derived from platelet-poor blood contains about 112 pg of the growth factor per mg of protein. As much as 1 .mu.g of the growth factor per mg of protein was recovered from human platelets by heating them at 100.degree. C for 2 min. Approximately 1-2 ng of the growth factor, in either whole serum or platelets, stimulates 5 to 10 .times. 103 confluent Balb/c-3T3 cells to replicate. The heat treatment of platelets allows the purification and quantitative recovery of the growth factor from blood.