CR2 and myasthenia gravis: For instance, the majority of autoantibodies causing MG are antiacetylcholine receptors (AChR) and AChR+CD21+ B cells in MG patients positively correlate with anti-AChR antibody production by ASCs in the serum [5], suggesting that hyperactivated antigen-specific B cell differentiation to ASCs represents a precursor of autoreactive ASCs.