Abstract
Background: The complement system plays a role in chronic immune activation during viral infections. Objectives: This study aimed to evaluate the levels of saliva and serum complements C3 and C4 in coronavirus disease 2019 (COVID-19) patients and healthy individuals. Methods: This cross-sectional study included 36 severe and 22 critical COVID-19 hospitalized patients and 22 healthy individuals. Serum and unstimulated salivary C3 and C4 levels were assessed using the immunoturbidimetric method and analyzed using one-way analysis of variance (ANOVA) with the Student-Newman-Keuls test as a post hoc analysis. Results: Salivary C3 and C4 levels were significantly lower in patients with severe and critical COVID-19 than in healthy individuals. There was no significant difference between the groups infected with severe and critical COVID-19. Serum C3 and C4 levels were lower in critical COVID-19 patients than in healthy individuals; nevertheless, no significant difference was observed between severe COVID-19 patients and healthy individuals. Additionally, serum C4 levels were lower in critical COVID-19 patients than in severe COVID-19 patients. Conclusions: It appears that serum and salivary C3 and C4 levels decrease in patients with COVID-19 infection.