Background information
Dendritic cells (DC) play a primary role in the immune system as antigen presenting cells. A key molecule, dendritic cell specific ICAM3 grabbing nonintegrin (DC SIGN1), is involved in regulating interactions between DC and resting T cells, including antigen presentation to T cells and enhancement of transinfection of CD4+ T cells by HIV 1. Efforts to identify additional type II membrane proteins resulted in the isolation of a related molecule named CD299, also known as DC SIGNR (DC SIGN Related), DC SIGN2, CD209L, and L SIGN (liver/lymph nodespecific ICAM3 grabbing nonintegrin). CD299 is located on Human chromosome 19p13.3 and shares 73-80% amino acid identity with DC SIGN1. Its structure is similar to DC SIGN1 and therefore binds mannose residues in a calcium dependent fashion, including ICAM3 and HIV 1 gp120. CD299 is polymorphic, since allelic variations of the exon 4 encoded sequence have been isolated. This is further supported by a study demonstrating the ability to isolate a large repertoire of CD299 transcripts largely the result of alternative splicing of the 7 coding exons. CD299 is primarily transcribed in the liver and lymph nodes but not in monocyte derived DC. Expression of CD299 is restricted to endothelial cells derived from liver sinusoids, lymph nodes sinuses, and capillaries, although variable expression in placenta and some monocytic cell lines has also been reported, including both membrane and soluble isoforms of the protein.
