Regulation of BCR expression on CLL cells by IL-4. CLL cells in peripheral blood have downmodulated BCRs, presumably to prevent inappropriate activation by antigen in the absence of co-stimulatory signals. In response to CXCL12 and other chemokines, these cells migrate to the lymph nodes, where locally secreted IL-4 induces CD79b and increases translocation of the BCR complex to the leukemic cell surface. This mechanism increases the likelihood that CLL cells encounter and interact with antigen in the appropriate context. IL-4R, IL-4 receptor. Professional illustration by Patrick Lane, ScEYEnce Studios.