A pituitary factor induces thymic epithelial cell proliferation in vitro.

Human thymic epithelial cells (TEC) were grown in culture and confirmed to be keratin positive (98-100%) and epidermal growth factor (EGF) responsive. Bovine pituitary extracts (BPE) stimulated the proliferation of TEC. The proliferation of TEC was confirmed by cell counts and radioautography. The BPE was active as measured by tritiated thymidine incorporation in the absence of serum and in the absence of EGF. Individual anterior pituitary hormones (growth hormone, prolactin, ACTH, FSH, LH, TSH) and posterior pituitary hormones (vasopressin and oxytocin) were inactive alone to stimulate TEC proliferation. The effect of EGF but not BPE was blocked by an antibody to EGF suggesting that the active component of BPE is not EGF. Purification of the factor is in progress. The observations suggest that this pituitary-derived factor(s) may regulate thymic function in vivo.