biostudies-literatureUnknown13Kowalska DNumerous publications have underlined the link between complement C5a and the clinical course of COVID-19. We previously reported that levels of C5a remain high in the group of severely ill patients up to 90 days after hospital discharge. We have now evaluated which complement pathway fuels the elevated levels of C5a during hospitalization and follow-up. The alternative pathway (AP) activation marker C3bBbP and the soluble fraction of C4d, a footprint of the classical/lectin (CP/LP) pathway, were assessed by immunoenzymatic assay in a total of 188 serial samples from 49 patients infected with SARS-CoV-2. Unlike C5a, neither C3bBbP nor C4d readouts rose proportionally to the severity of the disease. Detailed correlation analyses in hospitalization and follow-up samples collected from patienFrontiers in immunology946522https://www.ebi.ac.uk/biostudies/studies/S-EPMC9448977biostudies-literatureC5a elevation in convalescents from severe COVID-19 is not associated with early complement activation markers C3bBbP or C4d.PMC9448977Pio RYuste JROkroj MKowalska DSenent YTavira BInoges SKuzniewska ALopez-Diaz de Cerio AfalseC5a elevation in convalescents from severe COVID-19 is not associated with early complement activation markers C3bBbP or C4d.Numerous publications have underlined the link between complement C5a and the clinical course of COVID-19. We previously reported that levels of C5a remain high in the group of severely ill patients up to 90 days after hospital discharge. We have now evaluated which complement pathway fuels the elevated levels of C5a during hospitalization and follow-up. The alternative pathway (AP) activation marker C3bBbP and the soluble fraction of C4d, a footprint of the classical/lectin (CP/LP) pathway, were assessed by immunoenzymatic assay in a total of 188 serial samples from 49 patients infected with SARS-CoV-2. Unlike C5a, neither C3bBbP nor C4d readouts rose proportionally to the severity of the disease. Detailed correlation analyses in hospitalization and follow-up samples collected from patien2022-01-01T00:00:00Z20222025-04-04T07:15:35.789Z2025-04-04T07:15:35.789ZS-EPMC94489773609105710.3389/fimmu.2022.946522