Table 1.

Summary of the literature with the main findings of the basophil and mast cell involvement in COVID-19 pathogenesis.

Reference and Type of Study	No. of Patients	Main Results
Rodriguez et al. [42] Systems-level blood immune-monitoring study	37 patients	Basophils were depleted during acute disease but increase during recovery. Moreover, levels of basophils were significantly correlated with the titers of IgG antibodies to SARS-CoV-2.
Mao et al. [43] Observational study	127 patients admitted at Wuhan No. 1 Hospital	Basophil count was low in 17 (13.39%) patients during the first three days of hospitalization and returned to normal levels shortly after.
Fátima Conceição-Silva et al. [44] Review discusses the presence of ETs		ETs produced by neutrophils were associated with severity in SARS-CoV-2 infection favoring thrombosis. ET produced by basophils, which have bacteral killing and antifungal activity, could have a protective role during COVID-19 infection.
Ten-Caten et al. [45] A multidimensional analysis	178,887 Brazilian individuals, of which there were 33,266 positives for SARS-CoV-2	Lower counts of platelets, basophils, lymphocytes, and eosinophils were observed in COVID-19 cases compared with controls in both males and females.
Alnor et al. [46] Case–control study	74 COVID-19-positive and 228 COVID-19-negative patients.	COVID-19 patients presented significant lower values for all white blood cells, including basophil count, in comparison with non-COVID-19 patients.
Kazancioglu et al. [47] Retrospective case–control study	120 COVID-19 patients, 100 influenza patients, and 61 healthy controls	Lower basophil count was found both in COVID-19 and influenza patients compared to healthy controls.
Vitte et al. [48] Observational, prospective, multicentric, case–control study	26 patients	Low number of basophils were detected in COVID-19 patients as compared with healthy donors. Both CRTH2 (CD294), a receptor for prostaglandin D2, and CD11b expression were decreased at the surface of basophils. SARS-CoV-2 infection was associated with inhibition of T helper 2 polarized immune responses and a decreased chemotaxis of CRTH2+ cells, through reduction of basophils, eosinophils, and CRTH2 itself.
Chen et al. [49] Retrospective study	548 patients with COVID-19	A difference of basophil levels between admission and end-hospitalization greater than 0.02 × 109/L (HR, 2.73; 95% CI, 1.5–6.47) resulted a risk factor for fatal outcome.
Laing et al. [50] Observational study	63 patients	Basophils and dendritic cells are reduced in severe COVID-19. Basophil reduction correlate with elevated interferon-inducible protein-10.
Qin et al. [51] Observational study	452 patients admitted at Tongji Hospital	Severe COVID-19 patients had a lower percentage of basophils than non-severe ones (0.1 vs. 0.2%; p = 0.015).
Sun et al. [52] Mendelian randomization study	408,112 and 562,132 European subjectsfrom two different GWAS	Negative association between basophil count and basophil percentage of WBC are present in severe and hospitalized COVID-19 disease.
Motta et al. [53] Histopathological comparative control study	6 post-mortem covid patients, 10 post-mortem H1N1-infected patients, 10 patients who died for different reasons.	COVID-19 patients samples presented a significantly higher number of mast cells as compared con H1N1 patients and controls. In the context of a neutrophilic endothelitis, mast cells were more frequently localized in the perivascular spaces between the alveolar sacs and terminal bronchioles and in the alveolar septa, close to the alveolar capillaries.
Bahareh Hafezi et al. [54] cytokine response by mast cells during COVID-19.		MCs can respond to SARS-CoV-2 and accumulate in the lungs of patients with COVID-19, where they correlate with pulmonary edema, inflammation, and thrombosis.