(B) Mean motility coefficient of B lineage cells before (blue) and after (reddish) treatment with CXCR4 antagonists

(B) Mean motility coefficient of B lineage cells before (blue) and after (reddish) treatment with CXCR4 antagonists. reduced. Our experiments reveal that when immature B cells are near BM sinusoids their motility is usually reduced, their morphology is usually predominantly rounded, and cells reverse transmigrate across sinusoidal endothelium in a largely nonamoeboid manner. Immature B cell egress from BM was dependent on a twofold CXCR4 down-regulation that was antagonized by antigen-induced BCR signaling. This passive mode of cell egress from BM also contributes significantly to the export of other hematopoietic cells, including granulocytes, monocytes, and NK cells, and is reminiscent of erythrocyte egress. Leukocyte egress from lymphoid organs is usually a multistep process characterized by active cell migration mediated by pertussis toxin (PTX)Csensitive Gi proteinCcoupled receptors (GPCRs) toward exit sites, followed by reverse transmigration across endothelial barriers. Lymphocyte egress from thymus and lymph nodes is usually highly dependent on the chemoattractant lipid sphingosine 1 phosphate (S1P), which is usually abundant in circulatory fluids (blood and lymph) while limited in the lymphoid organ interstitium. The S1P gradient is usually sensed by lymphocytes through intrinsic expression of the PTX-sensitive GPCR S1P receptor 1 (S1PR1). S1PR1 deficiency causes 50C1,000-fold Tegafur reduction in T and B lymphocyte Tegafur figures in blood and lymph concomitant with their significant accumulation in lymphoid organs (Cyster and Schwab, 2012). S1PR1 mRNA expression is usually driven by the transcription factor Krppel-like factor-2 (KLF2) in developing thymocytes and Tegafur in naive T lymphocytes (Carlson et al., 2006; Bai et al., 2007). Of notice, KLF2 transcription is dependent around the FOXO1 transcription factor (Fabre et al., 2008; Gubbels Bupp et al., 2009; Kerdiles et al., 2009), and in T cells FOXO1 is usually sequestered in the cytoplasm and rendered transcriptionally inactive via phosphorylation mediated by the serine/threonine kinase AKT (Fabre et al., 2005). This molecular circuitry seems to ensure that only the negatively selected thymocytes undergoing low TCR signaling accomplish sufficient S1PR1 expression for exiting the thymus. In contrast, S1P and its receptors play a modest role in mediating cell egress from BM, as genetic or pharmacologically induced S1P receptor deficiency only accounts for approximately two- to threefold reduction in immature B lymphocyte, NK cell, and eosinophil export from BM (Walzer et al., 2007; Jenne et al., 2009; Allende et al., 2010; Pereira et al., 2010; Sugita et al., 2010). S1PR1 mRNA expression is largely impartial of KLF2 expressed in developing and mature B lymphocytes (Hart et al., 2011), thus making it unlikely that this S1P/S1PR1 egress pathway is usually under the control of BCR signaling induced in immature B lymphocytes during unfavorable selection in BM. The mechanism or mechanisms used by immature B lymphocytes for exiting BM thus remain essentially unknown. Whereas T cells comprise the vast majority of cells exported from your thymus, all other hematopoietic cells, and several nonhematopoietic cells, are produced in and exported from your BM. Neutrophils and monocytes use the GPCRs CXCR2 and CCR2 for BM egress, respectively; however, deficiency in either receptor reduced BM export by less than sevenfold (Serbina and Pamer, 2006; Eash et al., 2010; Shi et al., 2011). Why are lymphocytes highly sensitive to S1PR1-dependent mechanisms for exiting thymus and lymph nodes, whereas other Tegafur hematopoietic cells, including lymphocytes, are marginally dependent on single GPCR-dependent mechanisms for egress from BM? One possibility is usually that redundancy with multiple GPCRs controls egress of different cell lineages from BM. Alternatively, Gpr81 the fact that millions of reddish blood cells are produced and exported daily from BM (Lichtman and Santillo, 1986), and that these cells lack mechanisms for interstitial amoeboid cell migration, raises the possibility that alternative mechanisms control hematopoietic cell egress from Tegafur BM. CXCR4 is usually a PTX-sensitive GPCR.