Table 1. A summary of studies on NK cells in COVID-19.
| Title |
Sample |
Sample Size |
Results |
Ref. |
|---|---|---|---|---|
| Frequency | ||||
| Characteristics of peripheral lymphocyte subset alteration in COVID-19 pneumonia |
PB |
60 P, 245 HC |
NK cells in COVID-19 patients were significantly lower compared with HC. In severe cases, the number of NK cells was also lower than in patients in a mild situation |
[19] |
| Impaired NK cell counts and cytolytic activity in patients with severe COVID-19 |
PB |
10 P, 78 HC |
Impaired NK cell counts and their cytolytic activity was observed in COVID-19 patients compared with HC. Plus, the cytokines which are important for NK cells' activity, including IL-12, IL-15 and IL-21 were not detected. Besides, the serum level of soluble CD25 which is negatively correlated with percentages of NK cells was significantly elevated |
[17] |
| Immunologic perturbations in severe COVID-19/SARS-CoV-2 infection |
PB |
12 HC, 7 moderate P, 27 severe P, 6 recovered P |
Wide changes in NK cells during COVID-19. NK cells returned to normal range after recovery |
[14] |
| Unique immunological profile in patients with COVID-19 |
PB, BALF |
32 P, 25 HC |
Absolute NK cell count was significantly lower in COVID-19 patients compared with controls, whereas the NK cell frequency did not differ between the two groups |
[18] |
| NK cell activation related to clinical outcome of COVID-19 |
PB |
27 P, 17 HC |
Adaptive NK cell expansion was observed |
[16] |
| Single-cell landscape of bronchoalveolar immune cells in patients with COVID-19 |
BALF |
13 P, 3 HC |
The number of NK cells increased in BALF of COVID-19 patients |
[15] |
| Heightened innate immune responses in the respiratory tract of COVID-19 patients | BALF | 8 P, 146 CAP, 20 HC | The number of NK cells decreased in BALF of COVID-19 patients | [20] |
| Phenotype and function | ||||
|---|---|---|---|---|
| SARS-CoV-2 Spike 1 protein controls NK cell activation via the HLA-E/NKG2A pathway |
PB |
4 HC |
Intracellular expression of SARS-CoV-2 Spike protein 1 causes lower NK cell degranulation via the HLA-E/NKG2A pathway |
[21] |
| An inflammatory profile correlates with decreased frequency of cytotoxic cells in coronavirus disease 2019 |
PB |
48 P, 20 HC |
The number of NK cells expressing perforin decreased in patients in ICU |
[22] |
| Transplantation of ACE2 mesenchymal stem cells improves the outcome of patients with COVID-19 pneumonia |
PB |
10 (7 MSCs transplant, 3 Placebo) |
CXCR3 NK cells were increased significantly in comparison to HC which results in a cytokine storm. In contrast, in patients who underwent MSC transplantation, the overreacted NK cells disappeared |
[23] |
| Identification of druggable inhibitory immune checkpoints on NK cells in COVID-19 |
PB |
82 (10 HC, 10 paucisymptomatic COVID-19, 34 pneumonia, 28 ARDS due to COVID-19) |
The expression level of NKG2C remained intact |
[24] |
| Deletion of the NKG2C receptor encoding KLRC2 gene and HLA-E variants are risk factors for severe COVID-19 |
DNA from respiratory swabs |
361 P |
Patients with NKG2C/HLA-E variants are more susceptible to development of severe SARS-CoV-2 |
[25] |
| Unique immunological profile in patients with COVID-19 |
PB, BALF |
32 P, 25 HC |
The expression of NKG2D and DNAM-1, known as activating receptors of NK cells, was reduced in COVID-19 patients compared with HC |
[18] |
| A single-cell atlas of the peripheral immune response in patients with severe COVID-19 | PB | 7 P, 6 HC | Most COVID-19 patients’ NK cells expressed exhaustion markers, including LAG3, TIM-3, PDCD1 and HAVCR2 | [26] |
| Education | ||||
|---|---|---|---|---|
| NK cell activation related to clinical outcome of COVID-19 |
PB |
27 P, 17 HC |
No changes were observed in KIR receptors’ expression on NK cells |
[16] |
| Identification of druggable inhibitory immune checkpoints on NK cells in COVID-19 | PB | 82 (10 HC, 10 paucisymptomatic COVID-19, 34 pneumonia, 28 ARDS due to COVID-19) | Robust expression of KIR2DL1/S1 receptors on NK cells’ surface. Besides, No changes were observed in other KIR receptors | [24] |
ARDS: Acute respiratory distress syndrome; BALF: Bronchoalveolar lavage fluid; CAP: Community acquired pneumonia patients; HC: Healthy control; ICU: Intensive care unit; NK: Natural killer cell; P: Patient; PB: Peripheral blood.