Tumor necrosis factor α is necessary for granulocyte-macrophage-colony-stimulating-factor-induced eosinophil transendothelial migration

Background: We have previously shown that granulocyte macrophage-colony stimulating factor (GM-CSF) was capable of inducing eosinophil migration across naked filters but not endothelial monolayers. Tumor necrosis factor alpha (TNF-alpha) has been shown to be a key factor in granulocyte adhesion and transendothelial migration. Methods: We, therefore, pretreated human umbilical vein endothelial cell (HUVEC) monolayers with TNF-alpha and studied whether TNF-alpha could support GM-CSF-induced eosinophil transendothelial migration. Results: We found that TNF-alpha supported GM-CSF-induced eosinophil transendothelial migration and that this process was: (1) dependent upon GM-CSF and TNF-alpha dose; (2) time-dependent; (3) not due to TNF-alpha having a chemotactic effect itself; (4) not due to TNF-alpha-induced soluble factor production by endothelium, and (5) inhibitable by actinomycin D. We next studied the specificity of this response. Neutrophils did not migrate across TNF-alpha-pretreated endothelium in response to GM-CSF. TNF-alpha pretreatment of A549 human type-II-like epithelial lung cells (A549) did not support GM-CSF-induced transepithelial migration. Neither interleukin (IL)-1 nor GM-CSF pretreatment of the HUVEC supported GM-CSF-induced transendothelial migration. However, IL-5 induced eosinophil migration through naked filters as well as TNF-alpha-pretreated HUVEC in a manner analogous to GM-CSF. Antibodies to ICAM-1, but not VCAM-1 significantly inhibited this response. Although IL-1 did not support GM-CSF-induced eosinophil transendothelial migration, IL-1 and TNF-alpha induced equivalent expression of ICAM-1 on HUVEC. Conclusion: Thus, TNF-alpha-supported eosinophil transendothelial migration in response to GM-CSF (and IL-5) is dependent upon ICAM-1, and is both specific and complex.