Some of the convoluted pathways of antigen-induced B-cell differentiation. Naïve B cells (nBCs) express high levels of FOXP1. Antigen activation induces formation of germinal centers, extrafollicular plasma cells, and nonswitched memory cells (IgM mBCs) that express intermediate levels of FOXP1. Entry into germinal centers involves loss of FOXP1 expression,²  although some dark zone B cells do express FOXP1 (hatched). IgG-switched memory B cells (IgG mBCs) express lower levels of FOXP1 than nonswitched memory B cells, making them more likely to enter plasma cell differentiation on B-cell receptor stimulation.