Background:  The lectins DC-SIGN and DC-SIGNR augment infection by HIV, Ebola virus (EBOV), and other pathogens. The neck domain of these proteins drives multimerization, which is believed to be required for efficient recognition of multivalent ligands. The neck domain of DC-SIGN consists of 7 sequence repeats with rare variations. In contrast, the DC-SIGNR neck domain is polymorphic and, in addition to the wild type allele with 7 repeat units, allelic forms with 5 and 6 sequence repeats are frequently found. Whether DC-SIGNR alleles with fewer than 7 repeat units are associated with decreased risk of HIV-1 infection is currently under discussion. Therefore, we investigated if DC-SIGNR alleles with 5 and 6 repeat units exhibit defects in the interaction with pathogens.

Methods:  To analyze HIV transmission, lectin-expressing cells were inoculated with HIV-1 reporter virus, washed and co-cultivated with T cells. Infection efficiency was assessed after 72 hours by determining luciferase activity in cell lysates. The influence of the DC-SIGNR variants on EBOV glycoprotein (GP), Marburg virus (MARV) GP, or severe acute respiratory syndrome (SARS)-Coronavirus S-protein (SARS-CoV-S)-driven infection was analyzed by inoculating lectin-expressing cells with pseudotyped luciferase reporter viruses. Binding of the DC-SIGNR variants to soluble EBOZ-GP and SARS-CoV-S was determined via flow cytometry. To assess the multimerization status of the different variants on transfected 293T cells, Western blot experiments under reducing and non-reducing conditions were performed.

Results:  Here, we show that wild type DC-SIGNR and patient-derived alleles with 5 and 6 repeats bind viral glycoproteins, augment viral infection, and tetramerize with comparable efficiency. Moreover, co-expression of wild type DC-SIGNR and alleles with 5 repeats did not decrease the interaction with pathogens compared with expression of each allele alone, suggesting that potential formation of hetero-oligomers does not appreciably reduce pathogen binding, at least under conditions of high expression.

Conclusions:  Thus, our results do not provide evidence for diminished pathogen capture by DC-SIGNR alleles with 5 and 6 repeat units. Albeit we cannot exclude that subtle, but in vivo relevant differences remained undetected, our analysis suggests that indirect mechanisms might account for the association of polymorphisms in the DC-SIGNR neck region with reduced risk of HIV-1 infection.