Chemokines and leukocyte traffic.

Twenty years after the discovery of chemokines is an appropriate time to review leukocyte traffic and to assess the knowledge and opportunities that have arisen from countless studies of the large and tight-knit family of chemotactic proteins.

Unusual chemokine receptor antagonism involving a mitogen-activated protein kinase pathway.

Antagonism of chemokines on chemokine receptors constitutes a new regulatory principle in inflammation. Eotaxin (CCL11), an agonist for CCR3 and an attractant of eosinophils, basophils, and Th2 lymphocytes, was shown to act as an antagonist for CCR2, which is widely expressed on leukocytes and is essential for inflammatory responses. In this report we provide direct evidence for a novel mechanism how chemokine receptor function can be arrested by endogenous ligands. We show that binding of eotaxin to CCR2 stimulates the mitogen-activated protein kinases extracellular signal-regulated kinase 1/2 (ERK1/2). Activation of the mitogen-activated protein kinase kinase 1/2-ERK pathway is indispensable for eotaxin-mediated attenuation of CCR2 function, as inhibition of ERK phosphorylation abolishes the arresting effect. ERK is also activated by CCR2 agonists, e.g., monocyte chemoattractant protein-1 (CCL2). However, the involved pathways are different, although in either case coupling of CCR2 to pertussis toxin-sensitive heterotrimeric G proteins is necessary. The results are in agreement with the view that CCR2 could assume different activation states depending on the ligand it encounters. With respect to actin polymerization and calcium mobilization, the different activation states lead to agonistic and antagonistic responses. It is conceivable that the intracellular signal transduction pathway that is activated by eotaxin could cause an attenuation of proinflammatory responses mediated by CCR2.

CXC and CC chemokine expression in inflamed and noninflamed pelvic ileal pouch tissue.

BACKGROUND AND AIMS: Pouchitis is the major long-term complication after ileal pouch-anal anastomosis (IPAA) in patients operated on for ulcerative colitis. The cause is unknown, but both the history of ulcerative colitis and increased bacterial concentration are important factors. Chemokines are mediators for the recruitment of inflammatory cells to the site of inflammation. This study examined the tissue expression of a panel of specific chemokines and the corresponding recruitment of inflammatory cells in IPAA tissue with and without inflammation and after antibiotic treatment. PATIENTS AND METHODS: Biopsy specimens postoperatively from ulcerative colitis patients with IPAA were obtained by endoscopy. Biopsies were taken from 8 patients with noninflamed IPAA and from 14 patients with an episode of acute pouchitis, before and after antibiotic treatment. Biopsies were stained for CD68, CD3, elastase, eotaxin, IP-10, MCP-1, MCP-3, and IL-8 and analyzed by NIH Image analyzer. RESULTS: Expression of IL-8, MCP-1, MCP-3, and IP-10 was significantly higher in pouchitis than normal pouch. The expression of MCP-1, MCP-3 and IP-10 were significantly lower after antibiotic treatment. CONCLUSION: These data support the importance of chemokines for the leukocyte recruitment in pouch tissue during acute pouchitis.

Pivotal role of dendritic cell-derived CXCL10 in the retention of T helper cell 1 lymphocytes in secondary lymph nodes.

Various immune diseases are considered to be regulated by the balance of T helper (Th)1 and Th2 subsets. Although Th lymphocytes are believed to be generated in draining lymph nodes (LNs), in vivo Th cell behaviors during Th1/Th2 polarization are largely unexplored. Using a murine granulomatous liver disease model induced by Propionibacterium acnes, we show that retention of Th1 cells in the LNs is controlled by a chemokine, CXCL10/interferon (IFN) inducible protein 10 produced by mature dendritic cells (DCs). Hepatic LN DCs preferentially produced CXCL10 to attract 5'-bromo-2'-deoxyuridine (BrdU)+CD4+ T cells and form clusters with IFN-gamma-producing CD4+ T cells by day 7 after antigen challenge. Blockade of CXCL10 dramatically altered the distribution of cluster-forming BrdU+CD4+ T cells. BrdU+CD4+ T cells in the hepatic LNs were selectively diminished while those in the circulation were significantly increased by treatment with anti-CXCL10 monoclonal antibody. This was accompanied by accelerated infiltration of memory T cells into the periphery of hepatic granuloma sites, most of them were in cell cycle and further produced higher amount of IFN-gamma leading to exacerbation of liver injury. Thus, mature DC-derived CXCL10 is pivotal to retain Th1 lymphocytes within T cell areas of draining LNs and optimize the Th1-mediated immune responses.

Neutrophil Activation and the Role of Interleukin-8 and Related Cytokines.

Neutrophils are usually the first blood cells to enter inflammatory lesions. They accumulate in high numbers, and perform defence functions that often lead to tissue damage as a consequence of release of lytic enzymes and oxygen-derived radicals. Like other leukocytes, the circulating neutrophils are in a resting state and are recruited into inflamed tissues by chemotactic stimuli. Several types of chemotactic agonists are known. Their formation in the tissues depends on the type of inflammatory injury. A single type of agonist may act initially, but the recruitment process usually depends on several agonists, which can act in concert since they bind to distinct receptors. Once the neutrophils have migrated into a diseased tissue, phagocytosis usually concurs in the triggering of product release.