Morphological features of changes in peripheral olfactory structures in SARS-COV-2 coronavirus infection

Abstract

Coronavirus infection caused by the SARS-CoV-2 virus is an extremely important and urgent problem of modern medicine. It spreads quickly, has a high probability of a severe course and a large number of critical complications in patients from the risk group. The presence of pathognomonic symptoms, one of which is the development of hypo– or anosmia, makes it possible to quickly differentiate coronavirus infection from other acute respiratory viral infections, that is, to isolate the patient on time and begin correct treatment, taking all possible risks into account. The aim is to identify the morphological features of olfactory structural elements in patients with coronavirus disease (COVID-19) for a better understanding of the mechanisms of olfactory disorders development in coronavirus infection. Materials and methods. The basis of the work is a retrospective analysis of autopsy material, namely the mucous membrane of the upper parts of the nasal cavity (olfactory epithelium) and olfactory bulbs of nine deceased (4 women and 5 men) aged from 53 to 79 years with a laboratory-confirmed diagnosis of COVID-19 and anosmia in anamnesis. We used standard hematoxylin and eosin staining and immunohistochemical reactions in accordance with the TermoScientific protocols (USA) with antibodies to neurospecific beta-III tubulin (clone TuJ-1) and RnDsystems protocols with antibodies to olfactory marker protein (OMP) and angiotensin converting enzyme (ACE-2). To compare the results, a control group of 9 deaths (3 women and 6 men) aged from 59 to 68 years with a laboratory-refuted diagnosis of COVID-19 was formed. The causes of death of these patients were complications of diabetes, coronary heart disease and cerebrovascular disorders of the ischemictype. Results. The average age of the deceased with a laboratory-confirmed diagnosis of COVID-19 and a history of anosmia and the control group was 64.67 ± 7.73 and 62.33 ± 6.48 years, respectively. The expression of olfactory marker protein (OMP) and neurospecific beta-III tubulin (clone TuJ-1) was partially positive (40.89 (25.00–52.00) and 42.44 (29.00–55.00) cells in the field of view at a magnification of 200×, respectively) in seven out of nine sections of the olfactory mucous membrane of deaths with a laboratory-confirmed diagnosis of COVID-19 and anosmia in anamnesis. The reaction with antibodies to angiotensin converting enzyme (ACE-2) was focally or subtotally absent (34.33 (14.00–49.00) cells in the field of view at 200× magnification). There was expression of these three markers in control sections of the olfactory mucosa of a deceased with a laboratory excluded diagnosis of COVID-19 and no symptoms of anosmia (Mann–Whitney test, P < 0.05). In sections of olfactory bulbs of patients with COVID-19 weak (Mann–Whitney test, P < 0.05) expression of receptors for angiotensin-converting enzyme (ACE-2) (26.78 (15.00–39.00) cells in field of view at a magnification of 200×) was revealed in contrast to control sections (100.56 (94.00–107.00) cells in the field of view at a magnification of 200×). Conclusions. The development of anosmia in SARS-CoV-2 coronavirus infection has specific features. This may be due to the primary destruction of cells expressing receptors for the angiotensin-converting enzyme (ACE-2-positive: sustentacular cells of the olfactory mucosa, neurons of the olfactory bulbs). Subsequent dysfunction of olfactory cells (OMP- and TuJ-1-positive) is also possible.