Sars-Cov-2 Spike 1 protein control Natural killer cells activation via HLA-E/NKG2A pathway
cell biology immunology/immunity inflammation molecular biology
Authors: Bortolotti, D. et al.
Link to paper: https://www.researchsquare.com/article/rs-31860/v1
Journal/ Pre-Print: Research square
Tags: Immunology/Immunity, Inflammation, Molecular biology, Cell Biology
1. SARS-Cov-2 spike proteins 1 (SP1) and 2 (SP2), as well as the full spike trimer of previous SARS-CoV promote NK migration in vitro
2. SP1 promotes downregulation of classical HLA and upregulation of non-classical HLA-E in lung epithelial cell line via GATA3
3. SP1 loaded HLA-E (IEDB prediction) promotes NK cell exhaustion via NKG2A upregulation and HLA-E/NKG2A interaction
It has been published that SARS-Cov-2 patients have fewer NK cells that also display an exhausted phenotype. Here, Bortolotti and al. transfect bronchial epithelial cell line Beas-2B with SP1, SP2 from SARS-CoV-2 or full spike protein form SARS-CoV. SP1 expression alone downregulated classical HLAs in Beas-2B, while GATA3 driven expression of the non-classical HLA-E increased. One of the peptides in SP1 domain is predicted to bind HLA-E specifically. NK cells co-cultured with SP1 expressing Beas-2B upregulate NKG2A, an inhibitory ligand for HLA-E, and exhibit decreased CD107a expression and cytotoxic activity. Additionally, authors show that all spike proteins tested exert chemotactic activity on NK cells.
Impact for SARS-CoV2/COVID19 research efforts
Understand the immune response to SARS-CoV2/COVID19
The study shows how presentation of SP1 by non-classical HLA-E on lung epithelium could cause exhaustion of NK cells
· In vitro study
Strengths and limitations of the paper
Novelty: The study shows for the first time how SARS-Cov-2 SP1 could inhibit NK cell activation thus causing immune evasion
Standing in the field: Supports the literature in that immune evasion and impaired lymphocytes play a role in the pathogenesis of COVID-19. Also, it has previously been shown that NKG2A on the surface of NK cells was increased during COVID-19.
Appropriate statistics: No. Kruskal- Wallis inappropriate as N is too small. It compares mean sum of the ranks to measure whether any one of the test groups are different. It doesn't tell which groups are different, so it requires a post hoc. T test used as post hoc inappropriate as we don't know about the distribution. Welch post hoc would be suitable. Another option would be One-way ANOVA.
Viral model used: purified Spike proteins (SP1 and SP2 from SARS-CoV2) and full Spike from previous SARS-CoV
Translatability: remote- suggests that preventing NK cell exhaustion trough the inhibition of NKG2A with e.g. monoclonal antibody monalizumab would be a potential therapy
§ The author does not suggest a possible mechanism by which SP proteins could cause NK cell migration, there is lack of a negative control with a non-stimulating protein in high concentration in the transwell.
§ A high number of NK cells in Figure 1B are producing IFN-g even without stimulation and without BrefeldinA treatment, it is unclear what is activating this NK cells and if an isotype control has been used in the experiment.
§ In Figure 5D not only anti HLA-E and anti-NKG2A antibodies restore CD107a expression but also the isotype control, making the experiment impossible to interpret, also cytotoxicity is only analysed by %CD107a+ cells but not directly with cell killing assays
§ Authors test subunit 1 and 2 of SARS-CoV2 and the whole trimer in the case of SARS-CoV. Unclear why not the whole SARS-CoV2 trimer instead.
§ It would be nice to validate these observations regarding NK cell function with Beas 2B cells infected with SARS-CoV2