The follicle-associated epithelium (FAE) secretes chemokines important in the recruitment of various cell types including CCL20 (MIP-3α). CCL20 is chemotactic to the CD11b+ dendritic cells (DCs) distributed in the subepithelial dome regions of the Peyer’s patches, and mice deficient in the receptor for CCL20, CCR6, have been reported to be devoid of the CD11b+ DCs in the dome regions. Here, we describe another chemokine specifically secreted from the FAE of mouse Peyer’s patches, CCL9 (MIP-1γ, CCF18, MRP-2). By in situ hybridization, we demonstrated that CCL9 mRNA was expressed by the FAE but not by the villus epithelium. At the protein level, CCL9 was detected on the FAE and on extracellular matrix structures within the dome regions of the Peyer’s patches. By RT-PCR, we demonstrated that one of the putative receptors for CCL9, CCR1, was expressed by the Peyer’s patch CD11b+ DCs and in a chemotaxis assay, CD11b+ DCs migrated toward CCL9. To compare the abilities of the chemokines CCL20 and CCL9 to recruit CD11b+ DCs to the dome regions, we examined the in vivo distribution of these cells in CCR6-deficient, CCL9-blocked wild type, or CCL9-blocked CCR6-deficient mice. To our surprise, using a sensitive immunofluorescence analysis, we observed that CD11b+ DCs were present in the dome regions of the CCR6-deficient mice. In contrast, Ab neutralization of CCL9 in vivo resulted in significant reduction of the CD11b+ DC number in the subepithelial dome regions of Peyer’s patches of both wild type and CCR6 −/− mice. Taken together, these results demonstrate an important role of CCL9 in CD11b+ DC recruitment to the dome regions of mouse Peyer’s patches.

In the B cell lineage, CCR10 is known to be selectively expressed by plasma cells, especially those secreting IgA. In this study, we examined the regulation of CCR10 expression in terminally differentiating human B cells. As reported previously, IL-21 efficiently induced the differentiation of activated human CD19+ B cells into IgD−CD38+ plasma cells in vitro. A minor proportion of the resulting CD19+IgD−CD38+ cells expressed CCR10 at low levels. 1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3), the active metabolite of vitamine D3, dramatically increased the proportion of CD19+IgD−CD38+ cells expressing high levels of CCR10. The 1,25-(OH)2D3 also increased the number of CCR10+ cells expressing surface IgA, although the majority of CCR10+ cells remained negative for surface IgA. Thus, 1,25-(OH)2D3 alone may not be sufficient for the induction of IgA expression in terminally differentiating human B cells. To further determine whether 1,25-(OH)2D3 directly induces CCR10 expression in terminally differentiating B cells, we next performed the analysis on the human CCR10 promoter. We identified a proximal Ets-1 site and an upstream potential vitamin D response element to be critical for the inducible expression of CCR10 by 1,25-(OH)2D3. We confirmed the specific binding of Ets-1 and 1,25-(OH)2D3-activated vitamin D receptor to the respective sites. In conclusion, 1,25-(OH)2D3 efficiently induces CCR10 expression in terminally differentiating human B cells in vitro. Furthermore, the human CCR10 promoter is cooperatively activated by Ets-1 and vitamin D receptor in the presence of 1,25-(OH)2D3.

CCR6 is the only known receptor for the chemokine macrophage-inflammatory protein (MIP)-3α/CC chemokine ligand (CCL)20. We have shown previously that CCR6 is expressed on peripheral blood B cells, but CCR6 activity on these cells is low in in vitro assays. We report that MIP-3α/CCL20-induced calcium flux and chemotaxis can be enhanced significantly on peripheral blood and tonsillar B cells after activation by cross-linking surface Ag receptors. Of particular interest is the fact that the enhanced activity on B cells was not associated with an increase in CCR6 expression as assessed by levels of receptor mRNA, surface staining, or MIP-3α/CCL20 binding sites, or by a change in the affinity of the receptor for ligand. These data convincingly demonstrate that responses to a chemokine can be regulated solely by changes in the downstream pathways for signal transduction resulting from Ag receptor activation, and establish CCR6 as an efficacious receptor on human B cells.

Adult T cell leukemia is a mature CD4+ T cell malignancy which predominantly expresses CCR4 and is etiologically associated with human T cell leukemia virus type 1 (HTLV-1). Because HTLV-1 transmission depends on close cell-cell contacts, HTLV-1-infected T cells may preferentially interact with CCR4+CD4+ T cells for efficient viral transmission. In terms of gene expression and protein secretion, we found a strong correlation between HTLV-1 Tax oncoprotein and CCL22, a CCR4 ligand, in HTLV-1-infected T cells. Transient Tax expression in an HTLV-1-negative T cell line activated the CCL22 promoter and induced CCL22. Additionally, tax gene knockdown by small interference RNA reduced CCL22 expression in the infected T cells. These findings indicate that CCL22 is a cellular target gene of Tax. In chemotaxis assays, the culture supernatants of HTLV-1-infected T cells selectively attracted CCR4+CD4+ T cells in PBMCs. This was blocked by pretreating the supernatants with anti-CCL22 Ab or PBMCs with a synthetic CCR4 antagonist. In coculture experiments, primary CCR4+CD4+ T cells significantly adhered to Tax-expressing cells. This adhesion was blocked by the CCR4 antagonist or pertussis toxin. Interestingly, CCR4 was redistributed to the contact region, and in some cases, this was accompanied by a polarized microtubule-organizing center, which is an indicator of virological synapse formation, in the infected T cells. Finally, anti-CCL22 Ab treatment also blocked HTLV-1 transmission to primary CD4+ T cells in coculture experiments with HTLV-1 producer cells. Thus, HTLV-1-infected T cells produce CCL22 through Tax and selectively interact with CCR4+CD4+ T cells, resulting in preferential transmission of HTLV-1 to CCR4+CD4+ T cells.