We observed here that the expression of B lymphocyte chemokine (BLC/CXCL13) was markedly enhanced in the thymus and kidney in aged (NZB × NZW)F1 (BWF1) mice developing lupus nephritis, but not in similarly aged NZB and NZW mice. BLC-positive cells were present in the cellular infiltrates in the target organs with a reticular pattern of staining. CD11b+CD11c+ dendritic cells were increased in the thymus and spleen in aged BWF1 mice and identified as the major cell source for BLC. CD4+ T cells as well as B cells were dramatically increased in the thymus in aged BWF1 mice, whereas no increase was observed in aged NZB and NZW mice. B1/B2 ratio in the thymus was significantly higher than those in the spleen and peripheral blood in aged BWF1 mice. Interestingly, BLC showed preferential chemotactic activity for B1 cells derived from several mouse strains, including nonautoimmune mice. Cell surface CXCR5 expression on B1 cells was significantly higher than that on B2 cells. Thus, aberrant high expression of BLC by myeloid dendritic cells in the target organs in aged BWF1 mice may play a pivotal role in breaking immune tolerance in the thymus and in recruiting autoantibody-producing B cells in the development of murine lupus.

Cryptopatches (CP) are murine gut anatomical sites for generating thymus-independent intraepithelial T lymphocytes (IEL). However, it remains elusive how lympho-hematopoietic progenitor cells migrate from bone marrow (BM) into CP and differentiate into IEL. Here we show that mice reconstituted with BM-derived c-kit(+) cells express CCL25 (TECK)-intrakine gene, which reduces specifically the chemotactic response to CCL25 but not CXCL12 in the thymocytes. These mice exhibited a dramatic reduction of CP and IEL in the small intestine, and harbored conspicuously decreased numbers of c-kit(+) cells in the emaciated CP. In contrast, T cells in the thymic, splenic and lymph node compartments developed normally in these mice. Importantly, it was demonstrated that CD11c(+) dendritic stromal cells in CP expressed CCL25 and c-kit(+) Lin(-) BM cells displayed vigorous chemotactic response to CCL25. Furthermore, RT-PCR analysis detects mRNA expression of CCR9 in the c-kit(+) Lin(-) BM cells. Thus, these results demonstrate that the CCL25-CCR9 pathway is essential for CP formation and the consequent appearance of IEL.

We have recently established the culture system to generate dendritic cells (DCs) from murine Lin−c-kit+ bone marrow hematopoietic progenitor cells (HPCs) in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) + stem cell factor (SCF) + tumor necrosis factor-α (TNF-α). We present here the identification of two DC precursor subsets originated from HPCs with the phenotype of CD11b−/dullCD11c+ and CD11b+hiCD11c+ that develop independently at early time points (days 4 to 6) in the same culture conditions. Both of CD11b−/dullCD11c+ and CD11b+hiCD11c+ precursors could differentiate at day 10 to 14 into CD11b−/dullCD11c+ mature DCs with typical morphology, phenotype, and the ability to stimulate allogenic mixed leukocyte reaction (MLR). However, the endocytic capacity of fluorescein isothiocyanate-dextran was markedly reduced during the differentiation. CD11b−/dullCD11c+precursors expressed high levels of Ia, CD86, CD40, and E-cadherin molecules, but not c-fms transcript, and mature DCs derived from this precursor subset continue to express abundant E-cadherin antigen, a discernible marker for Langerhans cells. In contrast, CD11b+hiCD11c+ precursors expressed c-fms mRNA, but low levels of Ia, CD86, and E-cadherin, whereas CD40 was undetectable. CD11b−/dullCD11c+mature DCs differentiated from these precursors displayed abundant c-fms mRNA and nonspecific esterase activity. Interestingly, CD11b+hiCD11c+precursors, but not CD11b−/dullCD11c+precursors, may be bipotent cells that can be induced by M-CSF to differentiate into macrophages. All of these results suggest that CD11b−/dullCD11c+ and CD11b+hiCD11c+ cells are distinct DC precursors derived from Lin−c-kit+ HPCs, which differentiate into mature DCs through bifurcated and independent DC differentiation pathways.

Dendritic cells (DCs) are highly specialized antigen-presenting cells that distribute widely in all organs. DCs initiate the primary immune response and activate naive T cells and B cells responsible for the acquired immunity. In this study, CCR7 mRNA was proved to be expressed in DCs and their precursors derived from murine bone marrow-derived hematopoietic progenitor cells (HPCs), whereas CCR1 mRNA was expressed in both CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors. CCR6 mRNA was not detected in any murine DC populations. In agreement with the chemokine receptor mRNA expression by each population in the DC differentiation pathway, SLC (also termed as MIP-3β), one of the ligands for CCR7, strongly and selectively chemoattracted both CD11b−/dullCD11c+ and CD11b+hiCD11c+ DC precursors (days 6 to 7) and more mature DCs (days 13 to 14). We have recently found that transforming growth factor-β1 (TGF-β1), a cytokine that is essential for the appearance of Langerhans cells in the skin, polarizes murine HPCs to generate Langerhans-like cells through monocyte/macrophage differentiation pathway. We observed here that TGF-β1 not only inhibited the expression of CCR7 in DCs and DC precursors derived from HPCs, but also inhibited the migration of these cells in response to SLC. This is the first report describing the chemokine and chemokine receptors responsible for murine DC migration and downregulation of DC migration by TGF-β1.