Double-negative (DN) B cells: an under-recognized effector memory B cell subset in autoimmunity.

Human B cells could be divided into four classical subsets based on CD27 and immunoglobulin (Ig)D expression. Distinct from the other three well-studied subsets, CD27- IgD- B cells, also termed as double-negative (DN) B cells, have long been neglected. However, in recent years emerging evidence shows that DN B cells are unique memory B cells with important functions. They are expanded in a variety of diseases, especially in autoimmune diseases, contributing to the disease pathogenesis. Here, we briefly review the studies on DN B cells, including their origins, characteristics, subsets and roles in diseases, to try to bring new insights into this under-recognized B cell subset.