Membrane lectins enhance SARS-CoV-2 infection and influence the neutralizing activity of different classes of antibodies

Abstract

Investigating the mechanisms of SARS-CoV-2 cellular infection is key to better understand COVID-19 immunity and pathogenesis. Infection, which involves both cell attachment and membrane fusion, relies on the ACE2 receptor that is paradoxically found at low levels in the respiratory tract, suggesting that additional mechanisms facilitating infection may exist. Here we show that C-type lectin receptors, DC-SIGN, L-SIGN and the sialic acid-binding Ig-like lectin 1 (SIGLEC1) function as auxiliary receptors by enhancing ACE2-mediated infection and modulating the neutralizing activity of different classes of spike-specific antibodies. Antibodies to the N-terminal domain (NTD) or to the conserved proteoglycan site at the base of the Receptor Binding Domain (RBD), while poorly neutralizing infection of ACE2 over-expressing cells, effectively block lectin-facilitated infection. Conversely, antibodies to the Receptor Binding Motif (RBM), while potently neutralizing infection of ACE2 over-expressing cells, poorly neutralize infection of cells expressing DC-SIGN or L-SIGN and trigger fusogenic rearrangement of the spike promoting cell-to-cell fusion. Collectively, these findings identify a lectin-dependent pathway that enhances ACE2-dependent infection by SARS-CoV-2 and reveal distinct mechanisms of neutralization by different classes of spike-specific antibodies.

SARS-CoV-2 RBD antibodies that maximize breadth and resistance to escape

“…6e). Like other non-ACE2-competitive antibodies 31,32 , S2H97 neutralization is attenuated in cells that over-express ACE2 (Extended Data Fig. 6f).…”

“…6b), even more than is required to access the cryptic antigenic site II 15 . Like other antibodies that only bind the open RBD 30,31 , S2H97 induces rapid and premature refolding of spike into the post-fusion state (Fig. 2e), promotes S1 shedding of cell-surface-expressed spike (Extended Data Fig.…”

“…MA104 cells were a gift from Harry Greenberg. 293T-ACE2 cells are described in references 31 and 43 . Vero and MA104 cell lines tested negative for mycoplasma contamination.…”

“…To investigate the effect of ACE2 expression on S2H97 neutralization, Vero E6 cells were seeded at 20,000 cells per well in black clear-bottom 96-well plates. 293T-ACE2 cells 31 were seeded at 35,000 cells per well in black clear-bottom 96-well plates that had been pre-coated with poly-D-Lysine (Gibco). The next day, SARS-CoV-2 spike-pseudotyped VSV neutralizations with S2E12, S309 and S2H97 were performed as described above.…”

After the pandemic: perspectives on the future trajectory of COVID-19

“…Assays for neutralizing antibodies elicited by the spike protein, have been the primary measure of COVID-19 vaccine immunity. Most neutralization assays are variable across assay systems and cell lines 50,51 , which limits their use to define a correlate that spans clinical studies of different vaccines, and they do not distinguish between responses to different epitopes on the spike protein, some of which are highly immunodominant 52 . The establishment of a WHO international standard to allow normalization of data from different assays is an important step towards addressing this issue (www.who.int/teams/blueprint/covid-19).…”