Activation of human peripheral blood dendritic cells induces the CD86 co‐stimulatory molecule

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Abstract
Maximal T lymphocyte responses require presentation of antigen by major 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 critical co‐stimulatory pathway inducing T lymphocyte proliferation and cytokine secretion. Dendritic cells (DC) are potent APC for a primary T lymphocyte response and potential CD28/CTLA‐4 ligands on DC are, therefore, of particular functional relevance. In these experiments, the expression and function of the CD28/CTLA‐4 ligands B7.1 (CD80) and B7.2 (CD86) were examined on human blood DC. Resting DC populations directly isolated by immunodepletion of lineage marker‐positive cells lacked cell membrane expression of CD80 and expressed little or no CD86, although CD86, but not CD80 mRNA was detected by reverse transcription‐polymerase chain reaction analysis. In contrast, low‐density DC isolated after culture in vitro strongly expressed CD86 surface protein, but expressed limited or no CD80, although mRNA for both molecules were detected. Short‐term culture of directly isolated DC up‐regulated both CD80 and CD86 expression. Analysis of the kinetics of CD28/CTLA‐4 ligand induction showed that surface CD86 was present within 8 h, whereas CD80 antigen was first detected after 24 h of culture. The functional importance of CD28/CTLA‐4 ligand up‐regulation on DC during T lymphocyte interactions was demonstrated by the ability of both CTLA‐41g and CD86 monoclonal antibodies (mAb), but not CD80 mAb, to block an allogeneic mixed lymphocyte reaction stimulated by DC populations initially negative for CD80 and CD86. These results demonstrate that CD86 is both the earliest and functionally the predominant co‐stimulatory CD28/CTLA‐4 ligand on DC.