B Cell Develоpment (Mоser) The end gоаl of VDJ reаrrаngement in the bone marrow is to create a B cell receptor that is functional and safe (not autoreactive). (A) Which two B cell developmental stages coincide with (1) VDJ rearrangement and (2) surrogate light chain expression? (2 points) (B) Briefly describe the process of positive selection in the bone marrow. Name the receptor and ligands involved (if any), and the purpose of positive selection). (2 points) (C) Negative selection in the bone marrow ensures that the BCR is “safe” (not autoreactive). Name the receptor and ligands involved. What is one possible outcome of negative selection? (2 points) (D) Briefly describe the principle of allelic exclusion. Without allelic exclusion, how might positive or negative selection be compromised? (2 points)