What are the mechanisms that drive selection of B cell?

Only cells that express Igm heavy chain are selected to survive to become pre-B cells. Igm heavy chain and surrogate light chains are expressed on cell surface and associate with Iga and Igb to form pre-BCR complex. Pre-BCR complex is a first checkpoint for cells that express functional Igm heavy chain. It sends survival signals. If Igm heavy chain is failed to be made – pre-B cells will die by apoptosis= first checkpoint.