CXCL12 and infection: Our analyses indicated that the frequencies of PBs in peripheral blood of Enpp1−/− mice were within the normal range following immunization with NP-KLH or infection with C. chabaudi. Homing of PBs to the BM is mediated by the chemokine CXCL12 and the receptor CXCR4 on PC53 as well as adhesion molecules including integrins54.