TABLE 1.
Observed fluctuation in NK cells in adult COVID-19 patients.
| NK cell subsets | Observation | Analyzed patients | Compared group(s) | References |
| CD16+CD56+ | Reduction (%) | Deceased | Survivors | Cui et al., 2020 |
| Reduction (#) | Deceased | Survivors | Cui et al., 2020; Belaid et al., 2021 | |
| Reduction (#) | Pneumonia patients | HD | Wang F. et al., 2020 | |
| No change (#) | Severeη | Mild | Wang F. et al., 2020 | |
| Reduction (#) | Severeη | Mildζ/moderateθ | Belaid et al., 2021 | |
| Reduction (#) | Cases | HD | Jiang et al., 2020 | |
| CD16+ | No change (%) | Cases | HD | Taghiloo et al., 2021 |
| Reduction (#) | Severeη | Mildζ | Taghiloo et al., 2021 | |
| CD56+ | No change (%) | Cases | HD | Taghiloo et al., 2021 |
| Reduction (#) | Severeη | Mildζ | Taghiloo et al., 2021 | |
| CD56low | Reduction (%) | Criticalι | HD | Wilk et al., 2020 |
| CD56hi | Reduction (%) | Cases | HD | Wilk et al., 2020 |
| BAL NK cells | Reduction (%) | Severeη/Criticalι | Moderateθ | Liao et al., 2020 |
| Increase (%) | Moderateθ | HD | Liao et al., 2020 |
NK cell subset, peripheral blood NK cell subset analyzed in the reported studies; BAL, bronchoalveolar lavage; (%), as frequency values; (#), as absolute number; Cases, COVID-19 patients (irrespective of severity); HD, healthy donors.
ζPatients with clinical signs of pneumonia with one of the following: respiratory rate > 30 breaths/min, severe respiratory distress, or SpO2 < 90% on room air.
ηPatients experiencing the following: respiratory failure, respiratory rate > 30 bpm, oxygen saturation < 93% at rest, arterial partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) (PaO2/FiO2) ratio < 300 mmHg.
θFever, signs of airway disease, with or without a tomographic image indicating pneumonia.
ιAny of the following: requirement for mechanical ventilation, shock, or concomitant organ failure.