Chemokines — Chemotactic Cytokines That Mediate Inflammation

Chemokines are chemotactic cytokines that activate and direct the migration of leukocytes. There are two subfamilies, the CXC and the CC chemokines. We recently found that the CXC-chemokine stromal cell-derived factor-1 (SDF-1) is a highly efficacious lymphocyte chemoattractant. Chemokines act on responsive leukocyte subsets through G-protein-coupled seven-transmembrane receptors, which are also used by distinct strains of HIV-1 as cofactors for viral entry. Laboratory-adapted and some T-cell-line-tropic (T-tropic) primary viruses use the orphan chemokine receptor LESTR/fusin (also known as fusin), whereas macrophage-tropic primary HIV-1 isolates use CCR-5 and CCR-3 (refs 7-11), which are receptors for known CC chemokines. Testing of potential receptors demonstrated that SDF-1 signalled through, and hence 'adopted', the orphan receptor LESTR, which we therefore designate CXC-chemokine receptor-4 (CXCR-4). SDF-1 induced an increase in intracellular free Ca2+ and chemotaxis in CXCR-4-transfected cells. Because SDF-1 is a biological ligand for the HIV-1 entry cofactor LESTR, we tested whether it inhibited HIV-1. SDF-1 inhibited infection by T-tropic HIV-1 of HeLa-CD4 cells, CXCR-4 transfectants, and peripheral blood mononuclear cells (PBMCs), but did not affect CCR-5-mediated infection by macrophage-tropic (M-tropic) and dual-tropic primary HIV-1.

Chemotactic factors are postulated to direct emigration of lymphocytes from the blood stream into sites of inflammation. Members of a family of chemotactic cytokines, termed chemokines, have been shown to attract lymphocytes but efficacy, i.e., the maximal percentage of attracted cells, has been low. We have identified a highly efficacious lymphocyte chemotactic activity in the supernatants of the murine bone marrow stroma cell line MS-5 which attracts 10-fold more lymphocytes in vitro than currently described lymphocyte chemoattractants. Purification of this chemotactic activity revealed identity to stromal cell-derived factor 1 (SDF-1). SDF-1 acts on lymphocytes and monocytes but not neutrophils in vitro and is both a highly efficacious and highly potent mononuclear cell attractant in vivo. In addition, SDF-1 induces intracellular actin polymerization in lymphocytes, a process that is thought to be a prerequisite for cell motility. Since SDF-1 is expressed constitutively in a broad range of tissues it may have a role in immune surveillance and in basal extravasation of lymphocytes and monocytes rather than in inflammation.

The importance of eosinophils in the pathogenesis of bronchial asthma is not established. In an attempt to evaluate the role of eosinophilic inflammation in asthma, we compared 10 normal subjects with 43 patients with chronic asthma, 19 of whom had severe disease as assessed by a clinical scoring method described by Aas and by pulmonary-function tests. Eosinophils were counted in peripheral blood and bronchoalveolar-lavage fluid, and in biopsy specimens obtained from the patients and post mortem from 8 subjects without asthma, but not from the 10 normal controls. Eosinophil cationic protein was titrated by radioimmunoassay in the bronchoalveolar-lavage fluid from all subjects and studied by immunohistochemistry in the biopsy specimens. There was a significant increase in the number of peripheral-blood eosinophils in the patients that was correlated with the clinical severity of asthma (P less than 0.001) and pulmonary function (P less than 0.03). Levels of eosinophils and eosinophil cationic protein were increased in the bronchoalveolar-lavage fluid from the patients and were also correlated with the severity of asthma (P less than 0.001 and P less than 0.002, respectively). Hematoxylin-eosin staining of bronchial-biopsy specimens showed that intraepithelial eosinophils were present only in patients with asthma. Immunohistochemical analysis of eosinophil cationic protein revealed that normal subjects had only a few nondegranulated eosinophils deep in the submucosa, whereas all the patients had degranulated eosinophils beneath the basement membrane and among epithelial cells. In some patients there was a relation between the presence of degranulated eosinophils and epithelial damage. Eosinophilic inflammation of the airways is correlated with the severity of asthma. These cells are likely to play a part in the epithelial damage seen in this disease.