Background: The contribution of dendritic cells to mucosal HIV transmission may be largely mediated via surface expression of DC-SIGN, a C-type lectin, to which HIV envelope proteins selectively adhere. The adherence processes may be sensitive to inhibitors that interfere with the DC-SIGN-gp120 interaction.

Methods: A series of recombinant baculovirus constructs was generated to express various truncated forms of DC-SIGN as soluble proteins, all encoding only extracellular portions of the parent molecule. Two (2) additional deletion mutants that lacked the transmembrane domain but retained portions of the intracytoplasmic tail were generated. Constructs were expressed by infecting insect cells with recombinant baculovirus, and proteins derived from cellular pellets were solubilized and then purified by chromatography. The ability of soluble forms of recombinant DC-SIGN to inhibit HIV binding was evaluated in whole-cell and immobilized assay formats. The effect of soluble DC-SIGN on acute HIV‑1 infection was determined by virus end-point titration in activated CD4+ lymphocytes and by replication in GHOST co-receptor expressing cells.

Results: Five (5) different soluble DC-SIGN proteins were purified from baculovirus expression at concentrations of 100-200 mg/ml. The two constructs that maintained portions of the intracytoplasmic tail (modeled after naturally occurring spliced soluble DC-SIGN RNA) showed significantly improved solubility and release into the culture supernatant when transfected into 293 T-cells. Soluble DC-SIGN proteins displayed binding to HIV-1, as evidenced by an inhibition of HIV-1 binding to DC-SIGN on target cell surface or plastic, and to recombinant gp120 protein on plastic. Soluble DC-SIGN did not significantly alter end-point titration of HIV‑1 infection in purified CD4+ lymphocytes. However, an enhancement of HIV‑1 infection in R5 and X4 co-receptor expressing GHOST cultures was observed.

Conclusions: Soluble DC-SIGN proteins maintain their biological activity and can block HIV‑1 binding to cell-surface DC-SIGN. These soluble proteins will be useful agents for evaluating contributions of DC-SIGN in mucosal HIV transmission and may ultimately give rise to novel antiviral agents.