The ontogeny of bovine thymostimulin production in fetal and postnatal age.

The development of thymostimulin production in the bovine fetal thymus was determined, starting at month 2 of gestation until birth. Production of fetal thymostimulin, identified electrophoretically as a peptide with 4-5000 Da, started at month 4 of gestation and achieved its maximum expression three months after birth, followed by a rapid decrease until month 18. Thymus of fetuses from the early gestational phase (2-3 months) yielded no electrophoretically detectable thymostimulin band. Biological activity of the fractions, determined by increased E-rosetting, fairly correspond to the content of the 4-5000 Da peptide moiety.