Interleukin-8 (IL-8): The Major Neutrophil Chemotactic Factor in the Lung

A number of novel chemotactic cytokines are becoming increasingly recognized as important participants in the elicitation of specific inflammatory cells from the peripheral blood to sites of inflammation. Recent observations have now demonstrated that certain chemotactic cytokines possess specificity for the selected movement of individual immune/inflammatory cell populations. One of the more studied chemotactic cytokines is a neutrophil chemotactic factor identified as interleukin-8 (IL-8). This polypeptide mediator is produced in abundance by mononuclear phagocytic cells, as well as a number of non-inflammatory cells. This latter list includes both fibroblasts and epithelial cells. Moreover, the synthesis of IL-8 by fibroblasts and epithelial cells involves stimulus specificity, as the production of this mediator by non-inflammatory cells is dependent upon an initial host response. In the context of the lung, the alveolar macrophage appears to play a central role by generating factors, such as interleukin-1 and tumor-necrosis factor, which are potent stimuli for the induction of IL-8 by the lung fibroblasts and type II epithelial cells. The cascade-like interaction may lead to the rapid production of significant quantities of IL-8 by the lung and may selectively recruit neutrophils to the pulmonary interstitium and/or airspace. This sequence of events, which leads to cytokine networking in the lung, may be an important phenomenon for the generation of a major chemotaxin important to a variety of lung diseases.