The chemokine SLC is expressed in T cell areas of lymph nodes and mucosal lymphoid tissues and attracts activated T cells via CCR7.

Secondary lymphoid-tissue chemokine, SLC, also known as exodus-2 and 6Ckine, is a novel CC chemokine with selectivity for T lymphocytes and preferential expression in lymphoid tissues. We have studied its production, receptor usage and biological activities. High levels of SLC mRNA were detected in lymph nodes, the gastrointestinal tract and several gland tissues, but no expression was found by Northern blot analysis in freshly isolated or stimulated blood monocytes and lymphocytes, or neutrophils and eosinophils. In situ hybridization revealed constitutive expression of SLC in the T cell areas and the marginal zone of follicles in lymph nodes and the mucosa-associated lymphoid tissue, but not in B cell areas or sinuses. Comparison with immunocytochemical staining showed similarity between the in situ expression of SLC and the distribution of interdigitating dendritic cells but not with sinus-lining dendritic cells, macrophages or T lymphocytes. SLC induced chemotaxis of T lymphocytes and its activity increased considerably when the cells were conditioned with IL-2 or phytohemagglutinin (PHA). Under optimal conditions SLC had unusually high efficacy and induced the migration of up to 50 % of input T lymphocytes. SLC also induced Ca2+ mobilization in these cells. Similar responses were obtained with EBI1 ligand chemokine (ELC), and sequential stimulation with both chemokines led to cross-desensitization, suggesting that SLC acts via the ELC receptor, CCR7. This was confirmed using murine pre-B cells stably transfected with CCR7 which bound SLC with high affinity and showed chemotaxis and Ca2+ mobilization in response to both SLC and ELC. In T lymphocytes PHA and IL-2, which enhanced chemotactic responsiveness, also markedly enhanced CCR7 expression. In contrast to all known chemokine receptors, up-regulation of CCR7 by IL-2 was transient. A maximum was reached in 2-3 days and expression returned to initial levels within 8-10 days. The present study shows that SLC is constitutively produced within the T cell areas of secondary lymphoid organs and attracts T lymphocytes via CCR7.

B cell-attracting chemokine 1, a human CXC chemokine expressed in lymphoid tissues, selectively attracts B lymphocytes via BLR1/CXCR5.

Although most leukocytes, T lymphocytes in particular, respond to several different chemokines, there is virtually no information on chemokine activities and chemokine receptors in B lymphocytes. A putative chemokine receptor, BLR1, that is expressed in Burkitt's lymphoma cells and B lymphocytes was cloned a few years ago. Deletion of the gene for BLR1 yielded mice with abnormal primary follicles and germinal centers of the spleen and Peyer's patches, reflecting the inability of B lymphocytes to migrate into B cell areas. By screening expressed sequence tag DNA sequences, we have identified a CXC chemokine, termed B cell-attracting chemokine 1 (BCA-1), that is chemotactic for human B lymphocytes. BCA-1 cDNA encodes a protein of 109 amino acids with a leader sequence of 22 residues. The mature protein shares 23-34% identical amino acids with known CXC chemokines and is constitutively expressed in secondary lymphoid organs. BCA-1 was chemically synthesized and tested for activity on murine pre-B cells 300-19 transfected with BLR1 and on human blood B lymphocytes. In transfected cells, BCA-1 induced chemotaxis and Ca2+ mobilization demonstrating that it acts via BLR1. Under the same conditions, no activity was obtained with 10 CXC and 19 CC chemokines, lymphotactin, neurotactin/fractalkine and several other peptide ligands. BCA-1 was also a highly effective attractant for human blood B lymphocytes (which express BLR1), but was inactive on freshly isolated or IL-2-stimulated T lymphocytes, monocytes, and neutrophils. In agreement with the nomenclature rules for chemokine receptors, we propose the term CXCR5 for BLR1. Together with the observed disturbance of B cell colonization in BLR1/ CXCR5-deficient mice, the present results indicate that chemotactic recruitment by locally produced BCA-1 is important for the development of B cell areas of secondary lymphoid tissues.

Identification of CCR8, the receptor for the human CC chemokine I-309.

The nucleotide sequence for a putative chemokine receptor, termed TER1, ChemR1, or CKR-L1, was recently obtained by a polymerase chain reaction-based cloning technique. It encodes a protein of 355 amino acids that shows 32-45% sequence identity with human chemokine receptors. The gene was localized on human chromosome 3p21-24, the site for the genes for the five known CC chemokine receptors, suggesting that the natural ligand may be a CC chemokine. We have stably expressed this receptor in murine pre-B cells 300-19 and have tested their responsiveness to 20 human chemokines and some other potential agonists. The CC chemokine I-309 was the only agonist that selectively induced intracellular Ca2+ mobilization and chemotaxis in receptor-transfected 300-19 cells. Stromal cell-derived factor 1, which binds to murine CXCR4 expressed in parental as well as transfected 300-19 cells, served as positive control in the functional screening. The interaction of I-309 with TER1 was of high affinity as shown by 125I-I-309 binding (Kd of 1.2 nM) and transient [Ca2+]i changes at subnanomolar concentrations of agonist. Migration responses in receptor-transfected 300-19 cells was typically bimodal with maximal activity at 10 nM of I-309. These data demonstrate that TER1 (ChemR1 or CKR-L1) is the receptor for I-309, and we propose to call this receptor CCR8 in agreement with the current nomenclature for chemokine receptors. The expression of CCR8 in blood leukocytes and lymphocytes was analyzed by Northern blot. No transcripts were found in RNA from freshly isolated blood neutrophils, monocytes, cultured macrophages, and phytohemagglutinin-stimulated T lymphocytes, and a faint hybridization signal corresponding to the RNA species of 4 kb was obtained only with RNA from interleukin-2-treated T lymphocytes. CCR8 is unusual for its selectivity for a single chemokine, previously shown only for CXCR1 and CXCR4, which bind interleukin-8 and stromal cell-derived factor 1, respectively. Identification of the receptor for I-309 represents a significant progress in determining the function of I-309 in inflammation and disease.