Pathogenesis of autoimmune inflammation in COVID-19: a literature review

The literature review examines the mechanisms underlying formation of autoantibodies to angiotensin converting enzyme (ACE) in COVID-19. The similarity of the autoimmune processes revealed in the new coronavirus infection and the inflammatory reactions previously studied in experimental models is shown. Plausible ways for developing neurodegenerative and rheumatic diseases and rheumatic diseases in patients after a new coronavirus infection are presented. The results of clinical studies have shown that COVID-19 convalescent patients often have serum antibodies to ACE type 2 (ACE2-specific antibodies), which are absent in non-COVID-19 apparently healthy individuals. The authors note that higher level of such antibodies was paralleled with more severe COVID-19. ACE2 is known to catalyze the degradation of angiotensin I and angiotensin II, and also converts angiotensin II into angiotensin 1–7, which has vasodilating, anti-inflammatory, and antifibrotic effects. Accordingly, low ACE2 level along with anti-ACE2 antibodies imprints progression of inflammation and tissue fibrosis, which obviously markedly exacerbates the course of the infectious and inflammatory process and increases the severity of irreversible post-inflammatory changes. Intravenous administration of heterologous polyclonal antibodies against pulmonary ACE has been shown to cause acute fatal pulmonary edema. Autoantibodies to ACE2 cause a predisposition of patients with connective tissue diseases to constrictive vasculopathy, pulmonary arterial hypertension and persistent digital ischemia, which was noted in a number of patients with severe COVID-19. Thus, COVID-19 is a very complex process that involves not only classical infectious and inflammatory, but also autoimmune reactions in human body. COVID-19 severity depends on magnitude of internal organs and body systems impairment. Improper treatment can provoke or activate autoimmune processes, including rheumatic and neurodegenerative diseases, which should be taken into account when choosing treatment regimens, including cases of new SARS-CoV-2 variants. The information summarized in the literature review substantiates a need for using immunosuppressive therapy in case of deterioration in COVID-19 patients.