Adhesion to Fibronectin Prolongs Eosinophil Survival

We have investigated the effect of adhesion to fibronectin (Fn) on the survival of eosinophils in culture. Peripheral blood eosinophils from normal human donors were separated by immunomagnetic selection and cultured in RPMI on Fn-(100/~g/ml) coated microtiter plates for up to 96 h. Survival was measure1 by trypan blue exclusion. There was a significant enhancement of eosinophil survival with Fn as compared with both bovine serum albumin-coated and uncoated wells (p <0.05-0.01). Fn-induced eosinophil survival was comparable to that obtained with exogenous interleukin 3 (IL-3) or granulocyte/macrophage colony-stimulating factor (GM-CSF) and was inhibitable by antibodies against Fn, very late antigen 4 (VLA-4), IL-3, and GM-CSF. Supernatants from Fn-, but not BSA-coated wells contained picogram amounts of IL-3 and GM-CSF, and eosinophils cultured on Fn for 24 h expressed mRNA for GM-CSF as determined by in situ hybridization. Therefore, Fn prolongs eosinophil survival in culture by triggering autocrine generation of cytokines by eosinophils. Since neutrophils lack VLA-4, this could provide a partial explanation for the preferential accumulation of eosinophils at sites of allergic inflammation, as well as the predominant tissue localization of eosinophils in healthy individuals. E osinophils are believed to be important effector cells in the host response to infection with helminthic parasites (1) and to have proinflammatory effects in allergic inflammation , including asthma (2, 3). In healthy individuals, eo-sinophils reside mainly in the tissues, but the mechanism of tissue localization is incompletely understood. A number of adhesion pathways have been defined that could potentially mediate the transmigration of eosinophils through the vas-cular endothelium. The very late antigen 4/vascular cell adhesion molecule 1 (VLA-4/VCAM-1) pathway is of particular interest because it is not available to neutrophils (4-7). An alternative mechanism for eosinophil accumulation in tissues is prolonged survival. Like neutrophils, eosinophils are end-stage cells that in culture rapidly undergo cell death. However , eosinophil-active cytokines, such as I1.-3, I1:5, and GM-CSF, prolong eosinophil survival in culture for up to 2 wk (8, 9). They also enhance eosinophil functions such as cyto-toxicity for metazoan targets and mediator release (10). Activated eosinophils can also generate a number of cytokines in vitro (11, 12). mRNA for cytokines such as Ib5, GM-CSF, and TGF-cr has also been detected in vivo in various disease conditions (13, 14). The physiological triggers for eo-sinophil cytokine generation are not dear. ExtraceUular matrix proteins have been shown to modulate eosinophil response to physiological soluble stimuli (15). We have …