Evaluation of CD86/CD28 and CD40/CD154 Pathways in Regulating Monocyte-Derived CD80 Expression During Their Interaction With Allogeneic Endothelium

This study was designed to examine the role of monocyte-derived CD80 in providing costimulation to CD4+ cells, and to determine whether monocyte-derived CD80 expression is regulated by CD86/CD28 and CD40/CD154 pathways during allogeneic immunoresponses. Human endothelial cells (EC) and purified monocytes cocultured with or without CD4+ cells were analyzed by real-time quantitative polymerase chain reaction (RT-PCR) and florescence-activated cell scanning (FACS). Peripheral blood mononuclear cells (PBMC)-EC cocultures with or without costimulation blockade were analyzed by FACS. The effects of CD154 and CD28 blockade to inhibit lymphocyte proliferation were evaluated by mixed lymphocyte-EC reaction (MLER). RT-PCR demonstrated upregulation of CD80 transcripts in EC-stimulated monocytes in the absence of CD4+ cells. However, the surface expression of CD80 was undetectable. The expression of CD80 was restored in the presence of CD4+ cells. Additionally, CD80 blockade partially inhibited CD4+ cell proliferation induced by EC-conditioned monocytes. Monocytes demonstrated upregulation of CD80 on the surface during PBMC-EC interaction. CD86, CD28, and CD154 blockade did not prevent upregulation of monocyte-derived CD80 expression. CD28 and CD154 blockade partially inhibited lymphocyte proliferation of MLER. In summary, EC-stimulated monocytes upregulated CD80 expression at the transcript level but not on their surface in the absence of T cells. The surface expression of monocyte-derived CD80 is upregulated on EC-stimulated monocytes in the presence of T cells. CD154/CD40 and CD28/CD86 blockade cannot prevent monocyte-derived CD80 expression, suggesting that CD80 upregulation is through a CD154- or CD86-independent pathway. Specific therapy to prevent monocyte activation may be required for successful allograft transplantation.