Synthesis of nerve growth factor by L and 3T3 cells in culture.

Mouse submaxillary gland nerve growth factor (NGF) has been covalently joined to bacteriophage and the resulting phage conjugates remain biologically active in stimulating neurite extension from sensory ganglia. A sensitive bacteriophage immunoassay has been developed to measure concentrations of NGF as low as 1 ng/ml. With this method, we find that mouse L and 3T3 cells in culture produce a biologically active nerve growth factor that is immunologically similar if not identical to mouse submaxillary gland NGF. Since L cells are known to be a source of "conditioned medium" for tissue culture, it could be that one or more of the conditioning factor activities secreted by these cells are due to NGF itself.