The anti-TNF-alpha antibody infliximab indirectly regulates PECAM-1 gene expression in two models of in vitro blood cell activation

Chronic inflammatory bowel diseases can be successfully treated with antibodies against the acute phase mediator TNF-alpha. The process of activation and of extravasation of inflammatory cells from the blood into the 'stressed' tissue site is controlled by cytokines and chemokines, which attract leukocytes and by adhesion molecules, which mediate their attachment and transmigration toward the affected cell(s). The changes in the gene expression of adhesion molecules taking place in those cells before attachment have been less investigated. Changes of PECAM-1, ICAM-1 and vascular cell adhesion molecule-1 (VCAM-1) gene expression were studied in phytohaemagglutinin (PHA)- and lipolysaccharide (LPS)-treated human peripheral blood leukocytes (PBLs), granulocytes and the human monocyte cell line U-937. Cells were treated either with PHA or with LPS in the presence or absence of infliximab and incubated with TNF-alpha, IFN-gamma and/or transforming growth factor beta (TGF-beta) and treated as above. Activation of PBLs by PHA or LPS treatment triggered a sharp upregulation of ICAM-1, VCAM-1 gene expression and a time-dependent downregulation of PECAM-1 gene expression reaching a minimum 4 h from start of the experiment. The anti-TNF-alpha antibody infliximab, by neutralizing TNF-alpha and IFN-gamma production, completely reversed PECAM-1 mRNA downregulation and ICAM-1 and VCAM-1 upregulation. Immunostaining of PBLs cytospins with antibodies against PECAM-1 and ICAM-1 confirmed RT-PCR and western blot results. PBLs IFN-gamma or TNF-alpha treatment downregulated PECAM-1 in parallel with the upregulation of ICAM-1 and VCAM-1 gene expression, whereas TGF-beta upregulated PECAM-1- and downregulated ICAM-1 and VCAM-1 gene expression counteracting the effect of TNF-alpha or IFN-gamma. Similar results were obtained in human U937 cells and in granulocyte cultures by TNF-alpha or IFN-gamma treatment. Taken together, these results suggest that infliximab, blocking TNF-alpha and IFN-gamma production, exerts its anti-inflammatory effect through inhibiting downregulation of PECAM-1 gene expression and upregulation of ICAM-1 and VCAM-1 expression in leukocytes of the peripheral blood. These results also suggest that TGF-beta may thus be of therapeutic importance as an anti-inflammatory agent. Laboratory Investigation (2012) 92, 166-177; doi:10.1038/labinvest.2011.160; published online 31 October 2011