Aim: To compare the effect of the two types of TNF-alpha, transmembrane TNF-alpha (TM-TNF-alpha) and secreted TNF-alpha (sTNF-alpha) on the biological functions of monocytic cell line U937 so as to explore the role of TM-TNF-alpha in inflammation.
Methods: Effect of the two types of TNF-alpha on the functions of U937 cells, such as phagocytosis, accumulation of cytokines' mRNA, the level of cytoplasmic IkappaB-alpha and expression of ICAM-1, was compared by phagocytosis, RT-PCR, Western blot and FACS.
Results: sTNF-alpha was found to be able to promote markedly phagocytosis by monocytic U937 cells, enhance the mRNA accumulation of cytokines, such as TNF-alpha, IL-1beta and IL-8 mRNA, induce the degradation of IkappaB-alpha and the expression of adhesion molecule ICAM-1; while TM-TNF-alpha was shown to have no effect on the functions above of U937 cells. Furthermore, it seemed TM-TNF-alpha did not have a synergic action with sTNF-alpha when U937 cells was treated with both types of TNF-alpha.
Conclusion: The data above shows that sTNF-alpha can activate U937 cells, while TM-TNF-alpha has no influence. It suggests that the two types of TNF-alpha may play the different role in inflammation.