Background: While the pathogenesis of coronavirus disease MESHD 2019 (COVID-19) is becoming increasingly clear, there is little data on IgA response, the first line of bronchial immune defense. Objective: To determine, whether COVID-19 is associated with a vigorous total IgA response and whether IgA autoantibodies are associated with complications of severe illness. Since thrombotic events are frequent in severe COVID-19 and resemble hypercoagulation of antiphospholipid syndrome MESHD (APS), our approach focused on antiphospholipid antibodies SERO (aPL). Materials and methods: In this retrospective cohort study we compared clinical data and aPL from 64 patients with COVID-19 from three independent centers (two in Switzerland, one in Liechtenstein). Samples were collected from April 9, 2020 to May 1, 2020. Total IgA and aPL were measured with FDA-approved commercially available clinical diagnostic kits. Results: Clinical records of the 64 patients with COVID-19 were reviewed and divided into a cohort with mild illness (mCOVID, n=26 [41%]), a discovery cohort with severe illness (sdCOVD, n=14 [22%]) and a confirmation cohort with severe illness (scCOVID, n=24 [38%]). Severe illness was significantly associated with increased total IgA (sdCOVID, P=0.01; scCOVID, P<0.001). Total IgG levels were similar in both cohorts. Among aPL, both cohorts with severe illness significantly correlated with elevated anti-Cardiolipin IgA (sdCOVID and scCOVID, P<0.001), anti-Cardiolipin IgM (sdCOVID, P=0.003; scCOVID, P<0.001), and anti-Beta2 Glycoprotein-1 IgA (sdCOVID and scCOVID, P<0.001). Systemic lupus erythematosus MESHD Systemic lupus erythematosus HP was excluded from all patients as a potential confounder of APS. Conclusions: Higher total IgA and IgA-aPL were consistently associated with severe illness. These novel data strongly suggest that a vigorous antiviral IgA-response triggered in the bronchial mucosa induces systemic autoimmunity HP.