Eosinophils and COVID-19: diagnosis, prognosis, and vaccination strategies

Abstract

The unprecedented impact of the coronavirus disease 2019 (COVID-19) pandemic has resulted in global challenges to our health-care systems and our economic security. As such, there has been significant research into all aspects of the disease, including diagnostic biomarkers, associated risk factors, and strategies that might be used for its treatment and prevention. Toward this end, eosinopenia has been identified as one of many factors that might facilitate the diagnosis and prognosis of severe COVID-19. However, this finding is neither definitive nor pathognomonic for COVID-19. While eosinophil-associated conditions have been misdiagnosed as COVID-19 and others are among its reported complications, patients with pre-existing eosinophil-associated disorders (e.g., asthma, eosinophilic gastrointestinal disorders) do not appear to be at increased risk for severe disease; interestingly, several recent studies suggest that a diagnosis of asthma may be associated with some degree of protection. Finally, although vaccine-associated aberrant inflammatory responses, including eosinophil accumulation in the respiratory tract, were observed in preclinical immunization studies targeting the related SARS-CoV and MERS-CoV pathogens, no similar complications have been reported clinically in response to the widespread dissemination of either of the two encapsulated mRNA-based vaccines for COVID-19.

Ruling Out Coronavirus Disease 2019 in Patients with Pneumonia: The Role of Blood Cell Count and Lung Ultrasound

“…Detection of parenchymal consolidation is an expression of a more advanced stage of the disease [15]. When our analysis included in addition those patients who presented consolidations without B-lines, the diagnostic accuracy of LUS decreased with a slight change in sensitivity (88%; 95%CI, 79-94) but with significant reduction in specificity (24%; 95%CI, [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. In our study the diagnostic accuracy of basophils and eosinophils to rule out COVID-19 was much greater than that of LUS.…”

“…Severe lymphopenia is associate with delayed viral elimination and uncontrolled cytokine production, leading to influx of myeloid cells into the lungs [20,21]. In particular, lung influx of blood eosinophils, mediated by interferon-γ secretion, is the key mechanism of alveolar inflammation [16,22]. Eosinophil counts are related to the outcome of COVID-19 patients [23,24].…”

Emerging Evidence for Pleiotropism of Eosinophils

“…This could be prevented by the addition of delta inulin adjuvants or TLR agonists, skewing immune responses toward T1, inducing immunization without recruiting eosinophils [121,122]. Although past vaccines induced eosinophil disease, current SARS-CoV-2 vaccines have not caused lung eosinophil infiltration and accumulation to date [123].…”

Eosinophils and Bacteria, the Beginning of a Story

“…During SARS-CoV-2 infection, eosinopenia is observed in a significant percentage of hospitalized patients [ 52 ], and the levels of eosinophils present a clear increase from acute to recovery phases [ 53 ] suggesting that these cells play a key role during the critical stages of disease. SARS-CoV-2 infection promotes strong granulocyte-macrophage colony-stimulating factor (GM-CSF) responses (known to activate eosinophils) [ 53 ], and its severity is associated with the emergence of CD62L + eosinophils in response to IFNγ and the upregulated expression of PD-L1 on circulating eosinophils [ 54 ], suggesting that in this context lung resident eosinophils will be dampening pro-inflammatory responses. Consequently, although levels of eosinophils have not been proven to be the cause of severe COVID-19, there is a clear correlation between the decrease in eosinophils and the worsening of the prognosis.…”