Surface receptor 1)B cell antigen receotor(BCR) BCR/mlgM 了 Membrane Ig(mlg) Mature B cell: mlgM mlgD BCR-Iga/gβ complexMembrane Ig (mIg) Mature B cell： mIgM ＋ mIgD BCR-Igα/Igβ complex BCR/mIgM Surface receptor 1) B cell antigen receotor (BCR)