Differentiation and functional maturation of human CD14⁺ adherent peripheral blood monocytes by xenogeneic endothelial cells: Up-regulation of costimulation, cytokine generation, and toll-like receptors

Background. Dendritic cells (DCs) can be generated from peripheral blood mononuclear cells (PBMC) after stimulation with exogenous granulocyte-macrophage colony stimulating factor and interleuldn (IL)-4. Further, extravasation of monocytes through human endothelial cells can also cause differentiation, maturation, and expression of DC-specific phenotype. However, it is unclear whether human DCs can be generated from monocytes under the influence of xenogeneic endothelial cells in the absence of exogenous cytokines. We therefore analyzed and compared the effect of human and porcine endothelial cells on the differentiation of human monocytes into DC. Methods. Adherent peripheral blood CD14⁺ monocytes were cultured in the presence of different cytokine combinations, human or porcine endothelial cells, and smooth muscle cells, and analyzed for DC-specific antigen expression, antigen-presenting capacity, cytokine and chemokine generation, and expression of Toll-like receptors by flow cytometry and reverse transcription polymerase chain reaction. Results. Human monocytes express a DC-specific surface phenotype and efficiently present allo- and xenoantigens to allogeneic T cells after co-culturing with allogeneic and xenogeneic endothelial cells, respectively. Differentiation of monocytes under different stimulating conditions is also accompanied by the up-regulation of costimulatory molecules (CD40, CD80, CD86), adhesion molecules (CD54), human leukocyte antigen (HLA)DR, synthesis of cytokines tumor necrosis factor-α, IL12p70, IL-10, and differential expression of message for Toll-like receptors. Conclusions. Porcine aortic endothelial cells can provide immunostimulatory signals to human peripheral blood adherent monocytes similar to allogeneic endothelial cells through the participation of innate immune mechanisms.