The role of T cell costimulatory molecules in regulating monocyte-derived CD80 expression during theirinteraction with endothelial cells

Objective To study the role of monocyte-derived CDS0 in providing co-stimulation to T cells, and to determine the role of CD86/CD28 and CD40/CDI54 pathways in regulating monocyte-derived CDS0 expression during allogeneic immunoresponses. Methods Monocyte- endothelial cell (EC) and monocyte/CD4+ cell-EC co-cultures were established. Cells were collected after 72-h co-culture followed by FACS to detect the CD80 expression. Real-time quantitative polymerase chain reaction (RT-PCR) was performed to study monocyte-derived 0380 transcript expression. Peripheral blood mononuclear cell (PBMC)-EC co-cultures with or without anti-CD86, CD28, and CD154 antibodies were established and analyzed by FACS for the monocyte-derived CD80 expression. Mixed lymphocyte-EC reaction (MLER) was performed to determine the effects of CD154 and CD28 blockade in inhibiting lymphocyte proliferation to EC. Results FACS analysis confirmed absence of CDS0, CD86 and CD14 expression in resting and activated EC. RT-PCR demonstrated that EC-stimulated monocytes in the absence of CD4+ cells upregulated the CDS0 transcript expression, and the surface expression of CDS0 was undetectable as measured by FACS. The expression of CDS0 was restored when CD4 ～ cells were added into the co-cultures. Up-regulation of CDS0 was revealed on monocyte surface during PBMC-EC interaction. Anti-CD28 and anti-CD86 antibodies and anti- CD28 Fab did not prevent up- regulation of monocyte- derived CD 8 0 expression. Anti - CD 154 antibody did not inhibit CD80 up-regulation. CD28 and CD154 blockade partially inhibited lymphocyte proliferation of MLER. Conclusions Human monocytes play an important role during cell-mediated immune responses. EC-stimulated monocytes up-regulate the CD80 mRNA expression but not on their surface in the absence of T cells. The surface expression of monocyte-derived CD80 is up-regulated in EC-stimulated CD14+ monocytes in the presence of T cells. Up-regulation of the monocyte-derived C1)80 expression can not be prevented by CD154/CD40 and CD28/CI)86 blockade, suggesting that CD80 up-regulation is through CD154 or CD6 independent pathway. Specific therapy directed to prevent monocyte activation may be required for allograft transplantation. Key words: Endothelial cells;  Monocytes;  Antigens, CD80