MMP and MMP mRNA expression was increased in cells treated with and ngml IL. Culture supernatant collected from endothelial cells treated with medium containing IL showed higher levels of active MMP and MMP production. After hof incubation, plates were examined for capillary tube formation by microscopy.After hof incubation, plates were examined for capillary tube formation under an inverted microscope.We observed increased capillary tube formation in endothelial cells incubated with medium containing IL and FGF. It has been shown recently that CXCR is the putative receptor involved in mediating ELR CXC chemokinemediated angiogenic activity, which has, however, not been shown conclusively.Although earlier data clearly demonstrate that IL is a chemotactic and growth factor for endothelial cells, there have been dif culties in detecting IL receptors on endothelial cells.In this study, we report that both HUVEC and HMEC constitutively express CXCR and CXCR mRNA and protein.Earlier reports suggest that IL receptors are lost in culture, a concept that only recently has been contradicted by recent reports showed expression of both CXCR and CXCR on HUVEC.These cells responded differently for chemotaxis and induction of calcium mobilization to IL and stromal cellderived factor demonstrated differential expression and responsiveness of CXCR and CXCR by HMEC and HUVEC.This was the rst indication that IL receptors exist on endothelial cells in vitro and that they evoke behaviors that differ from those observed in leukocytes.We extend these studies to show that HUVEC and HMEC express CXCR and CXCR mRNA and protein.IL is widely expressed in tumor, stroma, and endothelial cells. Its autocrine and paracrine function has been shown to play an important role in angiogenesis. However, the direct role of IL in angiogenesis remains unclear.Since angiogenesis is essential for tumor progression and metastasis, these data suggest that IL plays an autocrineparacrine role in tumor growth and metastasis. Endothelial cell survival and programmed cell death are critical for maintenance of vascular structure in angiogenesis. When HUVEC were cultured in medium devoid of growth Tazobactam acid factors, large numbers of endothelial cells were dead after hin culture.However, adding IL to these cultures signi cantly enhanced the survival of cultured HUVEC.The observed differences could be due to differences in the cell lines used in these studies.The mechanism by which IL exerts its antiapoptotic effect is not clear.These data suggest that IL might regulate angiogenesis by modulating the endothelial cell Dextrorphan tartrate antiapoptosis pathway.Tumor angiogenesis is a complex process that is regulated by a balance between angiogenic and antiangiogenic factors. In the present study, the mRNA levels, as well as active MMP and MMP expression in endothelial cells, were enhanced by recombinant human IL, suggesting that IL is involved in the degradation of extracellular matrix, leading to endothelial cell migration, invasion, and capillary tube organization.In conclusion, IL may be a potential endothelial cell growth and survival factor, interacting through its receptors expressed by endothelial cells.The mechanism of IL regulation of angiogenesis may be in part due to enhanced proliferation and survival of endothelial cells by differential expression of antiapoptosis genes and in part by activation of MMP and MMP.