Fibroblast growth factor (FGF) and an FGF-like molecule in pituitary extracts stimulate thymic epithelial cell proliferation.

A bovine pituitary extract (BPE) induces thymidine incorporation into human thymic epithelial cells (TEC) in vitro. Previous data demonstrated that its effects resulted in epithelial cell replication and suggested that the active component of BPE was likely to be a growth factor, different from epidermal growth factor (EGF) and interleukin 1 (IL1). In this report we present evidence to identify the active component of BPE as a fibroblast growth factor (FGF) family member, based upon several criteria: a) Purified bovine and human recombinant FGF also enhanced TEC proliferation in vitro. b) Neutralization studies showed antigenic similarities between BPE and basic FGF. c) Biochemical analytical studies allowed purification of BPE by its affinity for heparin with elution at 3M NaCl, and gel filtration sizing yielded a 73 KD molecule with which basic FGF co-eluted. The isoelectric point was found to be between 6.3 and 6.6 and this is the only finding not consistent with the characterization of basic FGF as the factor responsible for the activity of BPE on TEC proliferation.