I. B cell ontogeny Development: in mammals, B lymphocytes develop and mature in bone marrow; in birds they have a specialized site of B-cell generation--- the bursa of Fabricius. About 5-15% of the circulating lymphoid pool are b cells There are two stages As g- independent stage---BM Ag-dependent stage---peripheral• Development：in mammals, B lymphocytes develop and mature in bone marrow; in birds, they have a specialized site of B-cell generation--- the bursa of Fabricius. • About 5-15％ of the circulating lymphoid pool are B cells. • There are two stages Ag-independent stage---BM Ag-dependent stage---peripheral I. B cell ontogeny