Effects of cytokine mixtures on the expression of adhesion molecules in human umbilical vein endothelial cells in an in vitro model of inflammation

Summary: As an essential early event in the activation of the immune system increased adherence of circulating neutrophils, lymphocytes and monocytes to the microvascular endothelium is observed. This situation is followed by migration of these cells through vessel walls and their accumulation at sites of tissue injury. This process is mediated by specific cell adhesion molecules being crucial to the generation of immune and inflammatory responses. In this report we demonstrate the effects of cytokine stimulation on endothelial adhesion molecules evoked by incubating HUVECs with two specific cytokine combinations both comprising IL-2, IL-6, IFN-g and TNF-a, which have been selected because they are elevated in the blood during rejection and infection processes. Combination I additionally includes IL-8, which is released by activated monocytes and macrophages and is suggested to be an important angiogenic mediator stimulating the proliferation and migration of endothelial cells. On the other hand, combination II contains the two anti-inflammatory cytokines IL-4 and IL-10, which are predominantely synthesised by Th2 cells. While IL-4 demonstrates multiple stimulatory and regulatory effects, IL-10 plays a pivotal part in the regulation of immune responses. Both cytokines block the synthesis of cytokines, such as IL-1, TNF-a and IL-12, which are of regulatory importance at the beginning of inflammatory processes. These cytokine mixtures are placed in the centre of our studies in order to elucidate their influence on the cell surface expression of a number of adhesion molecules on HUVECs, when combined in multi-component incubation cocktails. The application of these cytokine combinations results in comparable effects significantly increasing the mean fluorescence intensity (MFI) of VCAM-1, slightly up-regulating ICAM-1 surface expression accompanied by the induction of E- and P-selectin expression. These adhesion molecules play pivotal parts in the process of leukocyte transmigration. The experiments reveal a strong up-regulation of these cell surface antigens under conditions mimicing inflammation. This is an essential finding stressing the importance of endothelial cells during the activation of the immune system.