Unexpected Steps in Plasma-Cell Differentiation Ulf Klein, Riccardo Dalla-Favera  Immunity  Volume 26, Issue 5, Pages 543-544 (May 2007) DOI: 10.1016/j.immuni.2007.05.005 Copyright © 2007 Elsevier Inc. Terms and Conditions

Figure 1 Step-wise Differentiation of an Activated B Cell into a Plasma Cell The upper pathway summarizes the current view about plasma-cell differentiation, i.e., that Blimp-1 and IRF-4 act upstream of XBP-1. The lower pathway summarizes the findings of Kallies et al. (2007) in this issue of Immunity: an activated B cell instructed to differentiate into a plasma cell inhibits Pax5 function, which in turn releases the suppression of Xbp1 and the gene encoding the joining (J)-chain, resulting in low Ig secretion. Late in this preplasmablastic, Blimp-1-independent stage, Blimp-1 and IRF-4 are upregulated independently, eventually resulting in the generation of the CD138+ plasmablast that continues to produce surface Ig along with secreted Ig. High expression of XBP-1, Blimp-1, and IRF-4, the exclusive production of secreted Ig, and the distinctive morphology, characterized by large amount of cytoplasm, define the stage of the fully developed plasma cell. Immunity 2007 26, 543-544DOI: (10.1016/j.immuni.2007.05.005) Copyright © 2007 Elsevier Inc. Terms and Conditions