POLYMERASE CHAIN REACTION-BASED IDENTIFICATION OF A NOVEL SERPIN FROMHUMAN DENDRITIC CELLS

A subtraction library of CD40-stimulated human tonsil dendritic cells has been constructed using a polymerase chain reaction approach adapte d for low numbers of cells. From this library we identified a cDNA for a serine protease inhibitor, a serpin, which is absent from monocytes , B cells and T cells but expressed in CD40-activated monocyte-and pro genitor cell-generated dendritic cells. In addition, the serpin is exp ressed in a lung fibroblast cell line and keratinocytes. Its mRNA is d etected only in tonsil and thymus. The serpin described here reportedl y functions as a megakaryocyte maturation factor in the presence of in terleukin (IL)-3 and IL-11. This suggests that dendritic cells may pro mote the immune response by protecting IL-3 and IL-11 or other essenti al proteins from degradation.