Surface IgM-Inducing Factor in the Culture Supernatant of Bursal Epithelial Cells Derived from Chick Embryos

Bursal epithelial cells derived from 14-day-old chick embryos were cultured under a serum-free condition and the recovered culture supernatant was analyzed for surface immunoglobulin M (sIgM)-inducing activity on the bursacytes of 12-day-old chick embryos. Surface IgM positive rate of bursacytes incubated with the culture supernatant increased significantly, thus indicating the presence of sIgM-inducing factor(s) in the culture supernatant. The sIgM-inducing factor(s) in the supernatant was analyzed by gel filtration chromatography and HPLC. Results from these analyses indicated that the factor may be a polypeptide with a molecular weight of about 1300. This substance which is different from already known factors, such as Bursin, may be a newly discovered B cell differentiating factor in the bursa of Fabricius that promotes chicken B cell differentiation.