Innate Immunity in Children and the Role of ACE2 Expression in SARS-CoV-2 Infection.

Mario Dioguardi,Diego Sovereto,Antonio Dioguardi,Luigi Laino,Lorenzo Lo Muzio,Giorgia Apollonia Caloro,Angela Pia Cazzolla,Claudia Arena,Giuseppe Troiano,Vito Crincoli

doi:10.3390/pediatric13030045

Abstract

COVID-19 (Coronavirus Disease 2019) is an emerging viral disease caused by the coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), which leads to severe respiratory infections in humans. The first reports came in December 2019 from the city of Wuhan in the province of Hubei in China. It was immediately clear that children developed a milder disease than adults. The reasons for the milder course of the disease were attributed to several factors: innate immunity, difference in ACE2 (angiotensin-converting enzyme II) receptor expression, and previous infections with other common coronaviruses (CovH). This literature review aims to summarize aspects of innate immunity by focusing on the role of ACE2 expression and viral infections in children in modulating the antibody response to SARS-CoV-2 infection. This review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles deemed potentially eligible were considered, including those dealing with COVID-19 in children and providing more up-to-date and significant data in terms of epidemiology, prognosis, course, and symptoms, focusing on the etiopathogenesis of SARS-CoV-2 disease in children. The bibliographic search was conducted using the search engines PubMed and Scopus. The following search terms were entered in PubMed and Scopus: COVID-19 AND ACE2 AND Children; COVID-19 AND Immunity innate AND children. The search identified 857 records, and 18 studies were applicable based on inclusion and exclusion criteria that addressed the issues of COVID-19 concerning the role of ACE2 expression in children. The scientific literature agrees that children develop milder COVID-19 disease than adults. Milder symptomatology could be attributed to innate immunity or previous CovH virus infections, while it is not yet fully understood how the differential expression of ACE2 in children could contribute to milder disease.

Highlights

The main coronaviruses involved in outbreaks in the last 20 years were SARS-CoV in 2003 [1], MERS (Middle East Respiratory Syndrome) in 2012 [2,3], and SARS-CoV-2 in2019, which causes coronavirus disease 19 (COVID-19) [4].COVID-19 is an emerging viral disease caused by the coronavirus SARS-CoV-2, which leads to severe respiratory infections in humans
The articles considered potentially admissible were those dealing with COVID-19 in children that provided the most up-to-date and significant data regarding the epidemiology, prognosis, course, and symptoms of the disease, focusing on the etiopathogenesis in children
18 studies were included in the review that dealt with COVID-19 and the role of ACE2 expression in children (Figure 1)

Summary

Introduction

COVID-19 is an emerging viral disease caused by the coronavirus SARS-CoV-2, which leads to severe respiratory infections in humans. Animal studies on SARS-CoV infection have shown an age-dependent innate immune response, with non-human primates having more intense reactions with age than young adults [22]. It was initially reported that children developed a milder disease than adults [21,23,24,25,26]. This could be due to a collective loss of immune protection due to aging, which leads to cellular and molecular dysregulation of the innate immune system

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