Dendritic cells (DC) are specialist antigen presenting cells which capture antigens in the periphery, migrate centrally, and present the processed antigens in the context of major histocompatibility complex and appropriate co-stimulatory molecules to T lymphocytes for the initiation of an immune response. DEC-205 has been identified as a putative antigen-uptake receptor, which is expressed abundantly on mouse DC. The recently cloned mouse DEC-205 cDNA predicts a molecular structure which has a marked similarity to the macrophage mannose receptor. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA library screening, we obtained the full coding region of human DEC-205 cDNA from the Hodgkin's disease-derived L428 cell line. The predicted protein structure is a type I transmembrane protein of 1722 amino acids consisting of a signal peptide, cysteine-rich domain, fibronectin type II domain, ten carbohydrate recognition-like domains, transmembrane domain, and a cytoplasmic tail. Human DEC-205 is 77% identical to the mouse protein with completely conserved cysteines. The DEC-205 gene (LY75) was mapped to chromosome band 2q24 by somatic cell hybrid panel analysis and fluorescent in situ hybridization. Northern blot analysis detected 7.8 and 9.5 kilobase DEC-205 transcripts in myeloid, B lymphoid, and Hodgkin's disease-derived cell lines. RT-PCR analysis indicated that immature blood DC contain a barely detectable amount of DEC-205 transcripts but these were markedly increased upon differentiation/activation.