Adhesion of human U937 macrophages to phosphorylcholine-coated surfaces

A new type of amphiphilic phosphorylcholine (PC) polymer was used in this work to develop a cell culture surface that allows the attachment of U937 macrophages. The PC polymer was a random copolymer of N-isopropylacrylamide (45%), N-(phosphorylcholine)-N'-(ethylenedioxy-bis(ethyl)) acrylamide (41%), and the hydrophobic monomer N-(n-octadecyl) acrylamide (14%). Polypropylene (PP) films (1 cm2) were coated with the polymer solution by immersion. U937 macrophage suspensions were applied on PC polymer-coated surfaces and incubated for up to 72 h at 37 degrees C. While U937 cells did not adhere to PP, ammonia, nitrogen, or oxygen plasma-treated surfaces, they attached rapidly on PC-coated surfaces (< 1 h), proliferated, and stayed attached to the modified surface for at least 72 h, suggesting that unique features of the PC polymer, and the U937 macrophages, are responsible for the attachment of these cells. We compared the effect of Co2+ and Cr3+ ions on the expression of bone-resorbing cytokines (TNF-alpha, IL-6, IL-1beta) in U937 macrophages cultured on PC-coated surfaces to the response of U937 macrophages in suspension. Cytokine gene expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR). Addition of Co2+ and Cr3+ ions led to a significant increased expression of TNF-alpha in both cultured and suspension cells. On the other hand, Co2+ and Cr3+ ions had a weak stimulatory effect or no effect on IL-1beta and IL-6, respectively, in both cultured and suspension cells. In conclusion, the use of PC polymer-modified surfaces might offer promising new opportunities for the culture of human U937 cells and may also point to the mechanism by which macrophages interact with lipid bilayers of biological membranes.