The Glycan Ectodomain of SARS-CoV-2 Spike Protein Modulates Cytokine Production and Expression of CD206 Mannose Receptor in PBMC Cultures of Pre-COVID-19 Healthy Subjects

TL;DR

The glycan part of the SARS-CoV-2 spike protein affects cytokine production and a specific receptor in immune cells, suggesting a role in COVID-19 immunity.

Contribution

The study reveals novel immunomodulatory effects of SARS-CoV-2 spike protein glycans on cytokine production and CD206 expression in PBMCs.

Findings

Spike protein modulates IL-6 and IFN-γ production in PBMCs depending on antigen or mitogen stimulation.

S-hu protein up-regulates Con A-induced PBMC activation, while S-in protein down-regulates it.

Spike proteins and mannan upregulate CD206, a marker of anti-inflammatory M2 macrophages, in unstimulated PBMCs.

Abstract

The ability of recombinant, SARS-CoV-2 Spike (S) protein to modulate the production of two COVID-19 relevant, pro-inflammatory cytokines (IL-6 and IFN-γ) in PBMC cultures of healthy, pre-COVID-19 subjects was investigated. We observed that cytokine production was largely and diversely modulated by the S protein depending on antigen or mitogen stimulation, as well as on the protein source, insect (S-in) or human (S-hu) cells. While both proteins co-stimulated cytokine production by polyclonally CD3-activated T cells, PBMC activation by the mitogenic lectin Concanavalin A (Con A) was up-modulated by S-hu protein and down-modulated by S-in protein. These modulatory effects were likely mediated by the S glycans, as demonstrated by direct Con A-S binding experiments and use of yeast mannan as Con A binder. While being ineffective in modulating memory antigenic T cell responses, the S proteins and mannan were able to induce IL-6 production in unstimulated PBMC cultures and upregulate the expression of the mannose receptor (CD206), a marker of anti-inflammatory M2 macrophage. Our data point to a relevant role of N-glycans, particularly N-mannosidic chains, decorating the S protein in the immunomodulatory effects here reported. These novel biological activities of the S glycan ectodomain may add to the comprehension of COVID-19 pathology and immunity to SARS-CoV-2.

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