PRTN3 and COVID-19: However, no significant relationship was observed with serological markers of autoimmunity (ANA RF and ACPA).18 Additionally, in the study of Derksen et al.,5 the authors evaluated the prevalence of ACPA after COVID-19 by measuring ACPA IgG in 61 patients and concluded that the seroprevalence of this antibody did not increase after COVID.