MAG and rheumatoid arthritis: The involvement of memory B cells in a number of autoimmune disorders has been highlighted by the fact that repopulation of the B cell compartment after B cell depletion with memory B cells (as opposed with transitional, naive B cells) correlates with breakthrough disease activity or reemergence of antibodies, as shown in Myasthenia Gravis [15], anti-MAG neuropathy [16], rheumatoid arthritis (RA), and pemphigus [17–21].