ACTIVATION OF HUMAN PERIPHERAL-BLOOD DENDRITIC CELLS INDUCES THE CD86COSTIMULATORY MOLECULE

Maximal T lymphocyte responses require presentation of antigen by majo r histocompatibility complex molecules and delivery of one or more co- stimulatory signals. Interaction of the CD28 molecule on T lymphocytes with its ligands on antigen-presenting cells (APC) initiates a critic al co-stimulatory pathway inducing T lymphocyte proliferation and cyto kine secretion. Dendritic cells (DC) are potent APC for a primary T ly mphocyte response and potential CD28/CTLA-4 Ligands on DC are, therefo re, of particular functional relevance. In these experiments, the expr ession and function of the CD28/CTLA-4 ligands B7.1 (CD80) and B7.2 (C D86) were examined on human blood DC. Resting DC populations directly isolated by immunodepletion of lineage marker-positive cells lacked ce ll membrane expression of CD80 and expressed little or no CD86, althou gh CD86, but not CD80 mRNA was detected by reverse transcription-polym erase chain reaction analysis. In contrast, low-density DC isolated af ter culture ia vitro strongly expressed CD86 surface protein, but expr essed limited or no CD80, although mRNA for both molecules were detect ed. Short-term culture of directly isolated DC up-regulated both CD80 and CD86 expression. Analysis of the kinetics of CD28/CTLA-4 ligand in duction showed that surface CD86 was present within 8 h, whereas CD80 antigen was first detected after 24 h of culture. The functional impor tance of CD28/CTLA-4 ligand up-regulation on DC during T lymphocyte in teractions was demonstrated by the ability of both CTLA-4Ig and CD86 m onoclonal antibodies (mAb), but not CD80 mAb, to block an allogeneic m ixed lymphocyte reaction stimulated by DC populations initially negati ve for CD80 and CD86. These results demonstrate that CD86 is both the earliest and functionally the predominant co-stimulatory CD28/CTLA-4 l igand on DC.