Tolerance is the process by which white blood cells become educated not to react with your own body. This process first occurs in the bone marrow for B cells and the Thymus for T cells. This "central tolerance". If this does not occur there is also the chance of "peripheral tolerance" in the blood. These stop autoimmunity occurring.. In this study it is claimed that B cell tolerance in the blood fails and leads to the accumulation of potentially damaging B cells.
Is this the reason why MSers show enhanced B cell respponses after Alemtuzumab treatment.