Abstract
Hypervascularity is known as an important element of airway remodeling in bronchial asthma. However, it remains obscure how allergic inflammation relates to angiogenesis in the lung. In this study, we examined the in vitro effects of inflammatory cytokines on endothelial cell functions, particularly angiogenesis. Human microvascular endothelial cells from normal lung (HMVEC-Ls) were cultured with TNF-alpha, IFN-gamma, IL-4, a combination of TNF-alpha and IFN-gamma, or a combination of TNF-alpha and IL-4, and the cell proliferation and tube-forming activities were evaluated. IL-4 slightly enhanced the proliferation of HMVEC-Ls in the presence of vascular endothelial growth factor (VEGF), whereas TNF-alpha and IFN-gamma tended to inhibit it. Synergistic inhibition was observed when TNF-alpha and IFN-gamma were simultaneously added to the culture medium. The combination of IL-4 and TNF-alpha markedly promoted tube formation by HMVEC-Ls, even in the absence of VEGF. The IL-4 and TNF-alpha combination induced autocrine production of CXCR2 chemokines, which are known to have angiogenic activity, whereas the production of angiostatic CXCR3 chemokines was dramatically up-regulated when TNF-alpha and IFN-gamma were present. The marked IL-4- and TNF-alpha-induced tube formation was inhibited by a selective CXCR2 antagonist. These results suggest that, in the presence of TNF-alpha, IL-4 and IFN-gamma reciprocally regulate tube formation by HMVEC-Ls through autocrine synthesis of CXCR2 and CXCR3 chemokines, respectively. Of note, the CXCR2 chemokine-induced tube formation was independent of VEGF. Therefore, CXCR2 chemokines may represent potential therapeutic targets for bronchial asthma.