Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

The Systemic Immune Response in COVID-19 is Associated with a Shift to Formyl-Peptide Unresponsive Eosinophils

Version 1 : Received: 19 February 2021 / Approved: 22 February 2021 / Online: 22 February 2021 (10:33:05 CET)

How to cite: Koenderman, L.; Siemers, M.J.; Aalst, C.; Bongers, S.; Bindels, B.; Giustarini, G.; van Goor, H.; Kaasjager, K.; Vrisekoop, N. The Systemic Immune Response in COVID-19 is Associated with a Shift to Formyl-Peptide Unresponsive Eosinophils. Preprints 2021, 2021020453 (doi: 10.20944/preprints202102.0453.v1). Koenderman, L.; Siemers, M.J.; Aalst, C.; Bongers, S.; Bindels, B.; Giustarini, G.; van Goor, H.; Kaasjager, K.; Vrisekoop, N. The Systemic Immune Response in COVID-19 is Associated with a Shift to Formyl-Peptide Unresponsive Eosinophils. Preprints 2021, 2021020453 (doi: 10.20944/preprints202102.0453.v1).

Abstract

Background: A malfunction of the innate immune response in COVID-19 is associated with eosinopenia particularly in more severe cases. This study tested the hypothesis that this eosinopenia is COVID-19 specific and is associated with systemic activation of eosinophils.. Methods: Blood of 15 healthy controls and 75 adult patients with suspected COVID-19 at the ER were included before PCR testing and analyzed by point-of-care automated flow cytometry (CD10, CD11b, CD16 and CD62L) in the absence or presence of a formyl peptide (fNLF). 45 SARS-CoV-2 PCR positive patients were grouped based on disease severity. PCR negative patients with proven bacterial (n=20) or other viral (n=10) infections were used as disease controls. Eosinophils were identified with the use of the FlowSom algorithm. Results: Low blood eosinophil numbers (<100 cells/microL; p<0.005) were found both in patients with COVID-19 and with other infectious diseases albeit less pronounced. Two discrete eosinophil populations were identified in healthy controls both before and after activation with fNLF based on the expression of CD11b. Before activation, the CD11bbright population consisted of 5.4% (CI95% = 3.8, 13.4) of total eosinophils. After activation, this population of CD11bbright cells comprised nearly half the population (42.21%, CI95% = 35.9, 54.1). Eosinophils in COVID-19 had a similar percentage of CD11bbright cells before activation (7.6%, CI95% = 4.5, 13.6), but were clearly refractory to activation with fNLF as a much lower percentage of cells end up in the CD11bbright fraction after activation (23.7%, CI95% = 18.5, 27.6; p<0.001). Conclusion: Low eosinophil numbers in COVID-19 are associated with refractoriness in responsiveness to fNLF, which is likely caused by migration of fully functional cells to the tissue. Such homing might be beneficial as eosinophils have been implicated in viral killing.

Subject Areas

SARS-CoV-2; COVID-19; point-of-care flow cytometry; eosinophil; formyl peptide; responsiveness; blood; CD11b; CD62L

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