B7 BB-1 IS A LEUKOCYTE DIFFERENTIATION ANTIGEN ON HUMAN DENDRITIC CELLS INDUCED BY ACTIVATION/

Activation of a primary T-lymphocyte response requires additional sign als apart from interaction of the T-cell receptor (TcR)/CD3 complex wi th major histocompatibility complex (MHC) antigens on the antigen-pres enting cell. The CD28 antigen on T lymphocytes provides an important c o-stimulatory signal to T lymphocytes and we therefore searched for th e presence of its ligand, the B7/BB-1 antigen, on blood and tonsil den dritic cells (DC). Blood DC, prepared from peripheral blood mononuclea r cells with a minimal period of in vitro culture, did not stain with the monoclonal antibody BB-1 using flow cytometry analysis. In contras t, tonsil DC stained weakly for B7/BB-1 compared to positive control c ell lines. Polymerase chain reaction (PCR) was used to amplify a 605 b ase pair (bp) fragment from human B7/BB-1 m RNA and demonstrated signi ficant amounts of B7/BB-1 mRNA in tonsil DC but no specific product wa s obtained from blood DC, confirming the surface-staining results. Wea k expression of B7/BB-1 antigen was detected by immunofluorescence ana lysis following culture of blood DC with either interferon-gamma (IFN- gamma) or granulocyte-macrophage colony-stimulating factor (GM-CSF). T hese data support the concept that blood DC give rise to tissue and/or lymphoid DC, which acquire co-stimulatory ligands as a result of acti vation and/or differentiation.