Background: DC-SIGN, a specific C-type lectin expressed on dendritic cells, binds and transmits multiple strains of primate immunodeficiency viruses to susceptible cells. Under limiting amounts of cognate viral entry receptors, DC-SIGN can also facilitate the efficiency of virus infection when expressed in cis. Feline immunodeficiency virus (FIV) represents a complementary model for lentiviral pathogenesis. Thus, we sought to determine if DC-SIGN could function similarly in the FIV model.

Methods: To reduce the amount of background binding, CHO-pgsA745 cells (deficient in glycosoaminoglycans) were made to stably express DC-SIGN via retroviral transduction. FIV and HIV Env binding was performed on CHO-pgsA745 cells using Fc-fusion proteins in a FACS based assay. Virus binding and transfer experiments were performed using primary and lab-adapted isolates of FIV and a permissive feline T-cell line (104-C1). Cis-infection experiments were performed on parental versus DC-SIGN transduced 104-C1 T-cells, and virus replication monitored by an RT assay. Biochemical binding assays were performed using recombinant Envs and recombinant soluble DC-SIGN (ECD, Extracellular Carbohydrate-binding Domain). ECD was characterized to form the same ratios of tetramers as that found on dendritic cell-expressed DC-SIGN when compared using sucrose gradient fractionation analysis of ECD vs dendritic cell lysates.

Results: We report that DC-SIGN also captures feline immunodeficiency virus and allows infection of feline T-cells in trans. Furthermore, we show that cis expression of DC-SIGN facilitates FIV infection at low virus titers (MOI = 0.001). Thus, the ability of DC-SIGN to facilitate HIV infection in cis and in trans was recapitulated with the FIV model. The affinity of FIV Env (Kd = 1.03 + 0.26 nM) for recombinant soluble DC-SIGN was slightly higher than that for HIV Env (JRFL) (Kd = 2.98 + 0.49 nM) as determined by biochemical binding assays. Competition experiments indicate that FIV and HIV Envs were similarly sensitive to mannose-based inhibitors.

Conclusions: These results suggest that further investigation of the cat model and feline DC-SIGN may serve as a useful venue for study of the significance of DC-SIGN association to virus spread in a natural infection.