Antiphospholipid syndrome is a systemic autoimmune disease characterized by vascular thrombosis and/or complications in pregnancy in the constant presence of antiphospholipid antibodies. Antiphospholipid antibodies are involved in the pathogenesis of thrombosis in antiphospholipid syndrome through interactions with platelets, endothelial cells and monocytes. Such interactions result in changes in the target cell phenotype, which turns into prothrombotic. In monocytes and endothelial cells, these changes show as increased expression of inflammatory cytokines and tissue factor. In endothelial cells, the expression of adhesion molecules is also increased, which promotes interactions of endothelial cells with monocytes. Very few studies focused on the question whether these interactions are also promoted trough increased expression of adhesion molecules on the monocytes. The purpose of our study was therefore that in addition to the effect of antiphospholipid antibodies on the expression of inflammatory cytokines and tissue factor, we also investigate the effect of antiphospholipid antibodies on the expression of adhesion molecules on monocytes.
THP1 cells as well as monocytes isolated from blood were stimulated with IgG fractions of patients with antiphospholipid syndrome in the presence of lipopolysaccharide and the addition of prothrombin. First, we determined the appropriate stimulation conditions by which the activation of cells is achieved through measuring the amount of tumor necrotic factor α secreted into the cell environment. Later, using the defined stimulation conditions, the effects of antiphospholipid antibodies were evaluated. We measured secreted proinflammatory cytokines (tumor necrotic factor α, interleukin 6) by THP1 cells and monocytes, changes in the expression of genes for proinflammatory cytokines (tumor necrotic factor α, interleukin 6, 1β, 8) and tissue factor in THP1 cells and changes in the expressions of adhesion molecules (CD49d, CD11b, CD62L) on the surface of monocytes by flow cytometry.
Our results show that antiphospholipid antibodies in the presence of lipopolysaccharide activate monocytic cells, resulting in the increased expression of inflammatory cytokines, tissue factor, and altered expression of adhesion molecules. In THP1 cells, increased gene expression of tumor necrotic factor α and interleukin 6, 1β, 8 was measured. In addition, we measured increased secretion of tumor necrotic factor α and interleukin 6 into the cell environment of THP1 cells and monocytes. In THP1 cells we also measured increased gene expression of tissue factor. An altered profile of adhesion molecules was measured on monocytes, namely increased expression of CD49d and CD62L and decreased expression of CD11b.