Subtractive cloning of dendritic cell-specific genes: Identification of novel C-type lectins

To identify genes that are expressed selectively by dendritic cells (DC), we employed a subtractive cloning stategy in which a cDNA library constructed from the long-term DC line XS52 was subtracted with mRNA isolated from the J774 macrophage line. We have now cloned two novel cDNAs (1E4 and 1C 11-5) that encode new members of the C-type lectin family. Deduced amino acid sequences of 1E4 and ICI 1-5 represent distinct, but closely related, type II membrane-integrated receptors, consisting of: a) relatively short intracellular domains, b) transmembrane domains, and c) extracellular domains that exhibit extensive homology with the carbohydrate recognition domains (CRDs) of currently recognized C-type lectins. including the asialoglycoprotein receptor and CD23. Importantly, putative CRDs in both 1E4 and 1C11-5 contain 10 out of 13 invariant amino acids mat are relatively well conserved among C-type lectins. Both 1E4 and 1C11-5 mRNAs were expressed: a) abundantly in spleen and thymus, tissues known to contain DC in relatively large numbers, b) at high levels by the XS52 line, but not by other cell lines (including T cell, B cell, macrophage, keratinocyte, and fibroblast lines), and c) by freshly procured epidermal DC. We hypothesize that these two molecules, which presumably are expressed on DC surfaces, mediate the efficient uptake of glycosylated antigens. Further characterization of their function will provide important knowledge with respect to the biology of DC.