HUMAN EOTAXIN REPRESENTS A POTENT ACTIVATOR OF THE RESPIRATORY BURST OF HUMAN EOSINOPHILS

Increased numbers of eosinophils are found in parasitic infections, au toimmune diseases and allergic diseases such as allergic asthma. They are activated by distinct cytokines and chemokines leading to the immi gration in the inflamed tissue and mediate tissue damage by releasing reactive oxygen species. Here, the effect of the recently cloned CC ch emokine human eotaxin was investigated for its ability to affect diffe rent eosinophil effector functions and compared to the CC chemokines M CP-3 and RANTES. Human eotaxin induced chemotaxis of human eosinophils in a dose-dependent manner. The range of efficacy of the CC chemokine s compared to the well-known chemotaxin C5a was eotaxin = RANTES > MCP -3 = C5a. In addition, eotaxin induced rapid and transient actin polym erization, a prerequisite for cell migration, in eosinophils in the sa me range of efficacy as observed for chemotaxis. To investigate whethe r eotaxin was able to activate the respiratory burst of eosinophils, r elease of reactive oxygen species was measured by lucigenin-dependent chemiluminescence. Eotaxin induced production of significantly high am ounts of reactive oxygen species at a concentration between 10 ng/ml a nd 500 ng/ml. Surprisingly, the effect of eotaxin was comparable to th e well-known eosinophil activator C5a. The range of efficacy of the CC chemokines compared to C5a in the activation of the respiratory burst was eotaxin = C5a > MCP-3 > RANTES. Production of reactive oxygen spe cies was inhibited by pertussis toxin, staurosporin, genestein and wor tmannin. Furthermore, eotaxin induced transient increases in intracell ular calcium concentration ([Ca2+](i)) in human eosinophils. Therefore , pertussis toxin-sensitive Gi-proteins, protein kinase C, tyrosine ki nase, phosphatidylinositol-3-kinase and transient increases in [Ca2+]( i) are involved in the signal transduction of eosinophils following st imulation with eotaxin. In summary, this study reveals the importance of the CC chemokine eotaxin as a potent activator of the respiratory b urst, actin polymerization and chemotaxis. Eotaxin, therefore, plays a n important role not only by attracting eosinophils to the site of inf lammation but also by damaging tissue by its capacity to induce the re lease of reactive oxygen species.