Table 1.

Changes reported in the number/frequency of circulating or pulmonary neutrophils in patients, rodents or non-human primates infected with SARS-CoV, SARS-CoV-2 or MERS and their relationship with disease severity or clinical outcome.

	SARS-CoV	SARS-CoV-2	MERS-CoV
Blood	Humans Increased neutrophil/granulocyte counts and/or frequencies when compared to reference ranges (40, 41). Increased neutrophil count at hospital presentation is associated with ICU admission or death (42). Neutrophilia during hospitalisation is associated with an increased incidence of hospital-acquired bacterial infections (41). High neutrophil count at hospital admission is an independent predictor of severe illness (43). Increased neutrophil count in intubated Vs non-intubated patients (44). Rodents Increased neutrophil frequency when compared to pre-infection levels (45).	Humans Increased neutrophil counts and/or frequencies when compared to HCs (28, 29, 46, 47). Increased neutrophil counts in severe COVID-19 patients when compared to those with mild to moderate disease (48–51). COVID-19 non-survivors present at hospital admission with significantly elevated neutrophil numbers (52–54). High neutrophil count at hospital admission is an independent predictive factor for in-hospital death (55). Elevated neutrophil counts at hospital admission reported for patients who are later admitted to ICU (6). Neutrophilia is a risk factor for the development of ARDS and for the progression of ARDS to death (56).	Humans Increased neutrophil counts when compared to reference ranges (57, 58). Increased neutrophil counts in severe Vs. mild cases (59). Increased neutrophil count in non-survivors Vs. survivors (60). Rodents Increased neutrophil frequency and counts when compared to non-infected littermates (61). Neutrophil counts increase with disease severity (61). Non-human primates Increased neutrophil number post-infection (62).
Lungs	Humans Neutrophilic infiltrates in the lung (63). Rodents Increased neutrophil frequency in the lungs of infected mice (64).	Humans Intense neutrophilic infiltrate within the alveolar spaces and/or pulmonary vessels (37, 46, 65–68). Non-human primates Neutrophils accumulate in bronchial lumens, alveolar spaces and pulmonary lesions (69–72).	Humans High numbers of neutrophils detected in BALF samples (73). Non-human primates Neutrophil infiltration into the lungs (62, 74, 75).

ARDS, Acute respiratory distress syndrome; BALF, Bronchoalveolar lavage fluid; CoV, Coronavirus; COVID-19, Coronavirus disease 2019; HCs, Healthy controls; ICU, Intensive care unit; MERS-CoV, Middle East respiratory syndrome coronavirus; SARS, Severe acute respiratory syndrome.