Development and testing of radio and enzyme immunoassays for acidic fibroblast growth factor (aFGF)

Abstract Acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor from bovine brain stimulate growth in a variety of tissues in several species. Despite the 55% amino acid sequence homology of the two forms of FGF, a specific immunoassay of aFGF has been developed using a polyclonal antibody raised in a rabbit. Two immunoassays were compared: a radioimmunoassay (RIA) using 125 I aFGF and an enzyme immunoassay (EIA) using aFGF coupled to the tetrameric form of acetylcholinesterase (aFGF-AchE) as tracer. With EIA, the detection limit was 1.5 ng/ml, versus 2.2 ng/ml with RIA, while the dose at 50% was 5.9 ng/ml for EIA and 9.6 ng/ml for RIA. Using a modified EIA procedure where aFGF-AchE was added 2 h after the other reagents, the dose at 50% binding was 1.5 ng/ml. Examples of the performance of both immunoassays are presented for various brain extracts of different species including human. The aFGF content obtained by these methods correlates (CR = 0.987) with the values obtained by biological assay.