CXCL12 and infection: Systemic inflammation and infection down-regulate CXCL12 transcripts and protein levels in vivo (Ueda et al., 2004, 2005; Saw et al, 2019), whereas reduced CXCR4 function (CXCL12 receptor) in B-cell progenitors impairs B lymphopoiesis (Beck et al, 2014; Cordeiro Gomes et al, 2016; Mandal et al, 2019).