The mucosal immunity of the respiratory tract in COVID-19 convalescent healthcare professionals

<bold>Introduction:</bold> Most COVID-19 studies investigate changes in systemic immunity mechanisms, rather than in mucosal immunity - one that plays an important role defending against the respiratory pathogens. <bold>Aims and objectives:</bold> assessment of the respiratory tract mucosal immunity in healthcare professionals (HCPs) with COVID-19 history and ones without it. Materials and Methods: The cross-sectional study included 73 HCPs (65 females/8 males, mean age 47.1±12.3 years). There were four study groups: 1) severe disease (n=11), 2) moderate disease (n=21), 3) mild and asymptomatic disease (n=20), 4) no disease (n=21). The examination included saliva, induced sputum, nasopharyngeal, and oropharyngeal mucosa scrapings. Enzyme-linked immunosorbent assay determined secretory IgA (sIgA) (µg/L) and IgG (µg/mL) levels. The data are presented as Me (Q1; Q3). <bold>Results:</bold> Salivary IgA levels were higher (p<0.05) in patients of the 1st and 2nd groups (73.10 (64.15; 107.75) and 122.17 (67.53; 152.20) respectively) than in patients of the 3rd and 4th groups (56.73 (41.93; 76.31) and 2.09 (47.81; 73.06) respectively). Salivary IgG levels were higher in convalescent HCPs with severe (0.042 (0.015; 0.043)) and moderate (0.031 (0.011; 0.045)) disease in history compare to HCPs without COVID-19 (0.017 (0.04; 0.028), р<0.05). IgG levels in induced sputum samples were also higher in the 1st (0.025 (0.013; 0.036)) and the 2nd (0.018 (0.014; 0.040) groups compare to persons of the 4th (0.006 (0.000; 0.015)), p<0.05. <bold>Conclusions:</bold> The revealed changes indicate the residual inflammatory response of mucosal immunity in COVID-19 convalescents. The formation of a specific local immune response against the COVID-19 is also possible.