FOXP1 inhibits plasma cell differentiation

Abstract

After antigen contact, B cells rapidly differentiate and cycle through several phenotypical intermediaries before entering 1 of 2 longer-lived stages, the memory B cell or the plasma cell. In this issue of Blood, van Keimpema et al identify a role for the forkhead transcription factor FOXP1 in inhibiting the very last differentiation stage: plasma cell differentiation. They show that FOXP1 directly represses several key regulators of plasma cell differentiation. Although FOXP1 is strongly expressed in naïve B cells, it is lost as B cells enter germinal center differentiation. However, it is re-expressed in memory B cells where it correlates with immunoglobulin class switch recombination status, with immunoglobulin (Ig)G-switched memory B cells expressing lower levels of FOXP1. Interestingly, this correlates with a trait of IgG-switched memory B cells to being more likely to enter plasma cell differentiation3 (see figure).