DC-SIGN (CD209)
DC-SIGN (also called CD209) specifically expressed on the surface of
DCs, is a C-type lectin-like cell-surface receptor with multiple
functions. Its expression is also found in gastric and intestinal mucosa
and other epithelial cells. Initially, DC-SIGN was proved to only be a
pattern recognition receptor (PRR) and adhesion molecule for dendritic
cells to recognize pathogenic infections and participate in innate
immunity of organisms. Accumulating evidence has indicated that DC-SIGN
also act as the receptor of many viruses for infecting hosts and the
mediator of virus immune escape. Therefore, DC-SIGN has increasingly
become a research hotspot in the field of virology. Importantly,
DC-SIGN, together with other PRRs, can identify and capture viruses,
further swallow and store viruses to evade lysosome degradation, then
participate in antigen presentation, thereby achieving the mediation of
virus infection and dissemination in vivo. For instance, compared with
natural 3T3 cells, transfection of 3T3 cells with plasmids expressing
DC-SIGN renders the infection of infectious bronchitis virus (IBV) to be
significantly enhanced, while pretreatment with anti-DC-SIGN monoclonal
antibody inhibits IBV infection (Zhang, Buckles, & Whittaker).
Therefore, it has been speculated that the mannose carbohydrate residues
on the surface of coronavirus spike protein can bind to DC-SIGN receptor
and play an important role in the process of coronavirus infection (Z.
Y, E, & GR, 2012). Human aminopeptidase N (hAPN) has been confirmed to
be a cell receptor of HCoV-229E which is a common coronavirus of upper
respiratory tract. Similarly, a series of experiments have also
confirmed that HCoV-229E can use CD209L as one of its receptors
(Jeffers, Hemmila, & Holmes, 2006). Based on the similarity of the
sequence of HCoV-229E with that of PEDV, CD209L may be a receptor of
PEDV as well. However, substantial evidence is required to confirm this
concept in the future.