Effect of cell density on the expression of adhesion molecules and modulation by cytokines

Little is known about the regulation of integrin expression. Using flow cytometry, we have characterized the expression of integrin subunits and other adhesion molecules in bladder and colonic cell lines and studied their modulation by the cytokines tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). We show that although TNF-alpha and IFN-gamma may modulate integrin expression, these effects are, in the case of some integrin subunits, secondary to cytokine-induced changes in cell density. Cell density-dependent changes in the expression of alpha 2-, alpha 3-, alpha 6-, beta 1-, and beta 4-integrin subunits were seen. IFN-gamma produced density-independent decreases in expression of alpha 2- and beta 1-integrins and increases in expression of intercellular adhesion molecule-1 (ICAM-1), alpha 3-, alpha 6-, and beta 4-integrins. TNF-alpha produced increases in beta 1-integrin and ICAM-1 expression which were also density-independent. The expression of some integrin subunits is clearly density-dependent and the alterations seen are dependent on the cell line studied. This study illustrates the importance of including appropriate density-related controls in all investigations examining adhesion molecule expression.