Bursa of Fabricius is a very important organ for B-eell development. We sot bursa extracts from 2-3 months old Peking Duck. A partially purified PFC-stimulating active factor has been seperated from the extracts by twice molecular sieve chromatography, Sephadex G-15 and Moselect G-10. The M. W. of the active factor is below 750 dal. The results of HPLC analysis of the factor show that its polarity is relatively strong, and it has more positive charges.The works of purifying and looking for a new assay are still going on.

Bursa of Fabricius is the central organ of B-cell development in birds. There are some active factors in Bursa that are involved in the maturation of B lymphocytes. Bursa extracts from 2-3 month-old peking Duck, with a M. W. of 10,000 dal, can obviously increase the number of plaque-forming cells (PFCs) in normal or cyclophosphamidetreated mouse spleen. Cyclophosphamide (CP) is a kind of B-cell inhibitor. The extracts can also increase the life expectation of mouse treated with deathal dose of CP. These results show that Bursa extracts contain a factor (or some factors) which can promote the development or function of B cells. The factor is named as Bursatin. Because the PFCs-stimulating activity of the factor is susceptible to high temperature and pronase E, Bursatin is infered to be a peptide. The effect of Bursa extracts on elevating the cAMP level of mouse spleen cells suggests that Bursatin may function via cAMP. Besides, it is interesting that we have found that the extracts can also increase the rumber of E-rosett forming cells in pig thymocytes. The result shows that there are several active factors or certain factor poesses different activities in Bursa extracts.