Assessment of mucosal and systemic phagocytosis in Health Care Professionals (HCPs) in the post COVID-19 period

Phagocytic component of mucosal immunity in individuals infected with SARS-CoV-2 virus and COVID-19 convalescents is an understudied area. An important role in understanding haemophagocytic lymphohistiocytosis syndrome was played by the Russian researcher I.I. Mechnikov. <b>Aims and objectives:</b> To evaluate phagocytic component of respiratory mucosal immunity and a general level of phagocytic activity in blood of HCPs with COVID-19 history and ones without it. <b>Materials and methods:</b> Сross-sectional study included 182 HCPs (161 F/21 M, aged 47.3±12.7) after 125.1±71.1 days from the disease onset. Participants were divided into 4 groups: 1- severe, 2- moderate, 3- mild disease in history, 4- no disease. The examination included saliva, induced sputum, naso- and oropharyngeal mucosa scrapings, and venous blood samples. Phagocytic activity of blood leukocytes was determined by a cytofluometry flow in reaction with FITC-labeled staphylococci. Phagocytic activation index was determined by nitroblue tetrazolium reduction test. <b>Results:</b> The level of phagocytic index of granulocytes in the 2nd group (95,53±4,06) differed from the 3rd group (97,02±3,02) and from the 4th (97,44±1,89), p&lt;0,05. Reduced reserve of bactericidal activity was observed in persons of 1rd and 2nd groups (1.99±0.75 and 2.27±0.88 respectively) compare to the 4th group (2.71±1.37; p&lt;0.05). Values of phagocytic index of salivary granulocytes were lower in the group with severe disease (27,74±18,71) in comparison with HCPs without COVID-19 (48,82±27,42; p&lt;0,05). <b>Conclusion:</b> The revealed changes indicate dysregulation of the innate immune response in the post COVID-19&nbsp;period at the level&nbsp;of the mucosa as well&nbsp;as in blood.