As of August 16,2021,there have been 207,173,086 confirmed cases and 4,361,996 deaths due to the coronavirus disease(COVID-19),and the pandemic remains a global challenge.To date,no effective and approved drugs are available for the treatment of COVID-19.Angiotensin-converting enzyme 2(ACE2)plays a crucial role in the invasion into host cells by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),the etiological agent of COVID-19.Notably,ACE2 density is influenced by medical con-ditions,such as hypertension,or by drugs,including angiotensin-converting enzyme inhibitors(ACEIs)and angiotensin receptor blockers(ARBs),which can change the fate of SARS-CoV-2 infectivity.ACE2 is a target for these drugs and can be manipulated to limit the viral entry and replication within the cells.Different strategies aimed at blocking ACE2 with small molecules,peptides,and antibodies,or by neutralizing the virus through its competitive binding with human recombinant soluble ACE2(hrsACE2)are currently under investigation.In this article,we review the current state of knowledge that em-phasizes the need to find effective therapeutic agents against COVID-19 by exploiting ACE2 as a potential target.The increased soluble ACE2 levels and the application of hrsACE2 in patients with COVID-19 can be implemented to control the disease.It has not yet been established whether hypertension and other comorbidities,independent of age,have a direct role in COVID-19.Therefore,the use of renin-angiotensin system inhibitors,ACEls and ARBs,should not be discontinued during COVID-19 treatment.

BACKGROUND/AIMS: The existing histological classifications for the interpretation of small intestinal biopsies are based on qualitative parameters with high intraobserver and interobserver variations. We have developed and propose a quantitative histological classification system for the assessment of intestinal mucosal biopsies. METHODS: We performed a computer-assisted quantitative histological assessment of digital images of duodenal biopsies from 137 controls and 124 patients with celiac disease (CeD) (derivation cohort). From the receiver-operating curve analysis, followed by multivariate and logistic regression analyses, we identified parameters for differentiating control biopsies from those of the patients with CeD. We repeated the quantitative histological analysis in a validation cohort (105 controls and 120 patients with CeD). On the basis of the results, we propose a quantitative histological classification system. The new classification was compared with the existing histological classifications for interobserver and intraobserver agreements by a group of qualified pathologists. RESULTS: Among the histological parameters, intraepithelial lymphocyte count of ≥25/100 epithelial cells, adjusted villous height fold change of ≤0.7, and crypt depth-to-villous height ratio of ≥0.5 showed good discriminative power between the mucosal biopsies from the patients with CeD and those from the controls, with 90.3% sensitivity, 93.5% specificity, and 96.2% area under the curve. Among the existing histological classifications, our quantitative histological classification showed the highest intraobserver (69.7%–85.03%) and interobserver (24.6%–71.5%) agreements. CONCLUSIONS: Quantitative assessment increases the reliability of the histological assessment of mucosal biopsies in patients with CeD. Such a classification system may be used for clinical trials in patients with CeD.
Biopsy ; Celiac Disease ; Classification ; Cohort Studies ; Epithelial Cells ; Humans ; Intestine, Small ; Logistic Models ; Lymphocyte Count ; Observer Variation ; Sensitivity and Specificity