New insights into human B cell biology
B cells are highly important white blood cells known as lymphocytes and are part of the adaptive immune system. B cells have a specialised receptor on their cell surface (B cell receptor, BCR) which recognises specific proteins. Upon activation, B cells produce antibodies which bind antigens like e.g. molecules from pathogens or vaccines. The drawback of a vast range of different B cell receptors is the potential that some of the receptors recognise self-antigens which can then result in auto-immune disorders. The bone marrow continuously releases immature B cells into the blood stream. A high proportion of these so-called transitional B cells are able to recognise self-antigens via their BCR. It has been unknown where in the body these auto-reactive cells are checked and removed from the circulation. A recent publication by Anna Vossenkämper and Jo Spencer (King’s College) tracked the fate of human transitional B cells and identified that these cells localise to the gut-associated lymphoid tissue, a special immune compartment in the intestine. The authors found that transitional B cells become activated in the gut which may form an important step in the removal of auto-reactive B cells from the circulation. The authors further observed that transitional B cells from patients with the auto-immune disorder lupus erythematosus are poorly equipped to access the gut. In lupus, auto-reactive B cells are not efficiently removed from the circulation and attack self-antigens which results in inflammation in e.g. kidneys, blood vessels and joints. Thus, activation of immature B cells in GALT may function as a crucial checkpoint that protects against autoimmunity. This finding is of high importance and will help to gain a better understanding of human B cell biology and the pathogenesis of auto-immune conditions.