CD40L activation of dendritic cells down-regulates DORA, a novel member of the immunoglobulin superfamily.

Using a cDNA subtraction technique, a novel member of the immunoglobulin superfamily was isolated from human Dendritic cells (DC). This cDNA which we named DORA, for DOwn-Regulated by Activation encodes a protein belonging to the CD8 family of receptors containing a single V type loop domain with an associated J chain region, a transmembrane region containing an atypical tyrosine residue and a cytoplasmic domain containing three putative tyrosine phosphorylation sites. The hDORA gene has been localised to chromosome 16. From database searches a rat cDNA was identified that encoded a polypeptide with 63% identity to hDORA. The expression of the human cDNA was studied in detail. Northern blot analysis revealed 1.0 kb and 2.5 kb mRNAs in peripheral blood lymphocytes, spleen and lymph node, while low levels were observed in thymus, appendix, bone marrow and fetal liver. No signal was noted in non-immune system tissues. By RT-PCR analysis of hDORA revealed expression in cells committed to the myeloid lineage but not in CD34+ precursors or B cells and low expression in T cells. Expression was also observed in DC, purified ex vivo or generated in vitro from either monocytes or CD34+ progenitors. This was down-regulated following activation both by PMA and Ionomycin treatment and also by CD40L engagement. In situ hybridisation performed on tonsil sections showed the presence of hDORA in cells within Germinal Centers. This structure and expression suggests a function as a co-receptor, perhaps in an antigen uptake complex, or in homing or recirculation of DC.