To better understand the molecular mechanisms of dendritic cells (DC) function, we isolated differentially expressed genes in Ag-activated DC by a PCR-based subtractive hybridization technique. A novel fall-length cDNA, KE04, was thus isolated from KLH-activated human PBMC-derived DC. KE04 cDNA encoded a 346-aa protein devoid of functionally indicative motifs, KE04 protein showed 64% identity with a Caenorhabditis elegans protein and 83% identity with a human putative protein. Distant relationship was also found with other prokaryotic and eukaryotic proteins. Differential expression of KE04 in activated DC other than nonactivated DC was confirmed at both mRNA and protein levels. KE04 mRNA expression was detectable in various human tissues and cell lines by Northern blot and RT-PCR, Western blot and confocal microscopy analysis indicated that its cytolocalization was intracellular. Our data suggest the potential involvement of KE04 in DC activation and will facilitate the research of molecular mechanism of DC function.