Attachment of human immunodeficiency virus (HIV) to the cell surface can occur independently of envelope (Env) protein interactions with CD4, the major HIV type 1 (HIV-1) receptor. A variety of cell surface molecules have been shown to support virus attachment and to increase the efficiency of virus infection (10
). Cellular proteins incorporated into virus particles can also impact virus attachment and infection efficiency (3
). DC-SIGN is a type II integral membrane protein that avidly binds primary and lab-adapted HIV-1, HIV-2, and simian immunodeficiency virus (SIV) strains but does not, by itself, mediate virus infection (5
). Rather, DC-SIGN appears to function as a universal attachment factor for primate lentiviruses. Binding of DC-SIGN to Env is dependent largely if not exclusively on carbohydrate recognition, involving interactions between the lectin binding domain of DC-SIGN and the gp120 subunit of Env (5
). It is not known if DC-SIGN also binds to the gp41 transmembrane domain subunit. A closely related homologue of DC-SIGN, termed DC-SIGNR (17
), also binds and transmits multiple virus strains (1
DC-SIGN is of particular interest because its expression is largely restricted to immature dendritic cells (DCs) and certain types of macrophages in vivo (6
; E. J. Soilleux, L. S. Morris, G. Leslie, J. Chehimi, J. Trowsdale, L. J. Montaner, R. W. Doms, D. Weissman, N. Coleman and B. Lee, submitted for publication). Natural ligands of DC-SIGN include ICAM-3 and ICAM-2, indicating that DC-SIGN may play an important role in DC trafficking and in interactions with naïve T lymphocytes (4
). In addition, DC-SIGN can mediate binding of virus to DCs in vitro and once bound virus can remain infectious for days (5
). Interestingly, virus bound to DCs via DC-SIGN can be efficiently presented or transmitted to receptor-positive cell types (5
). This finding raises the possibility that DC-SIGN-positive DCs may serve as a conduit for HIV transmission, providing a mechanism by which virus can usurp the normal trafficking pathways of DCs and be delivered from mucosal surfaces to lymphoid organs (5
). Thus, it will be important to further characterize the expression patterns of DC-SIGN in vivo and the mechanisms by which DC-SIGN interacts with and transmits virus. In addition, it will be important to study DC-SIGN homologues from species used as animal models for HIV and AIDS and from mice, as this species affords an opportunity to study the normal functions of DC-SIGN in vivo.
In this study, we report the cloning of rhesus macaque, pigtailed macaque, and murine DC-SIGN. Rhesus and pigtailed macaque DC-SIGN proteins were highly similar to human DC-SIGN. By contrast, murine DC-SIGN exhibited significant homology to human DC-SIGN in the lectin binding domain and transmembrane domain of the protein but not in other regions. All three of these proteins bound ICAM-3 as well as HIV and SIV strains. In addition, rhesus and pigtailed macaque DC-SIGN molecules could transmit bound virus to receptor-positive cell types. By contrast, virus bound to murine DC-SIGN was not transmitted to receptor-positive cells, indicating that binding of virus to a C-type lectin protein does not always result in efficient virus transmission. Using a bacterial fusion protein as an immunogen, we produced and characterized a panel of monoclonal antibodies (MAbs) to DC-SIGN, identifying antibodies to at least two determinants in the repeat region, to the lectin binding domain, and to the extreme C terminus of the protein. One of the MAbs was DC-SIGN specific—it did not cross-react with human DC-SIGNR. Nearly all of the MAbs reacted with DC-SIGN on the surface of peripheral blood-derived DCs (PBDCs), and many cross-reacted with pigtailed and/or rhesus macaque DC-SIGN. None reacted with murine DC-SIGN. Our results indicate that DC-SIGN from rhesus and pigtailed macaques is functionally and antigenically similar to human DC-SIGN, while murine DC-SIGN exhibits important sequence and functional differences. The DC-SIGN-specific MAbs described here will be useful for studying DC-SIGN and DC-SIGNR expression patterns in vitro and in vivo in humans and nonhuman primates.