-Autoantibodies against nuclear antigens are detectable in 25% of patients hospitalized with 2 acute COVID-19, and are more common in severe illness. rapid autoimmune responses, characterized by production of self-reactive autoantibodies. In 20 this study, we tested specimens from acutely ill patients hospitalized with COVID-19 for 21 autoantibodies against nuclear, vasculitis-associated, and phospholipid antigens. Detectable 22 autoantibodies were present in 30% of the patients in our cohort, with the majority of reactive 23 specimens demonstrating antibodies to nuclear antigens. However, antinuclear antibodies were 24 only weakly reactive and directed to single antigens, as is often seen during acute infection. We 25 identified strongly reactive antibodies to nuclear antigens only in patients with a prior history of 26 autoimmune disease. In our cohort, the prevalence of antiphospholipid antibodies was low, and 27 we did not detect any vasculitis-associated autoantibodies. We found similar levels of 28 inflammatory markers and total immunoglobulin levels in autoantibody positive versus negative 29 patients, but anti-SARS-CoV-2 antibody levels were increased in autoantibody positive patients.
Together, our results suggest that acute COVID-19 is not associated with a high prevalence of 31 clinically significant autoantibody responses of the type usually associated with autoimmune 32 rheumatic disease. 
In addition to nuclear antigens, many other self-antigens can be targeted by autoantibodies in 60 association with diverse autoimmune phenomena, including vasculitis and thrombosis.
Histologic evidence of vasculitis has been described in COVID-19, suggesting the possibility 62 that autoimmune-mediated vessel diseases may occur [12, 13] . In addition, coagulopathy and 63 thrombosis is a prominent feature of severe COVID-19 [14] . Case reports suggest that 64 antiphospholipid antibodies can mediate autoimmune thrombosis in this disease [15] . 
Our previous reference range studies using specimens from healthy regional blood donors 167 obtained prior to the COVID-19 pandemic demonstrated a 12% positivity rate using the 168 manufacturer's cutoffs; all but one specimen was positive for only a single antibody.
healthy control samples produced quantitative results that were marginally above the manufacturer's suggested threshold. Based on these results, we established laboratory-defined would have been reported as positive for anti-nuclear antibodies, and these were the two with a The coagulopathy seen in patients with COVID-19 raises concerns that anti-phospholipid 188 antibodies may play a contributing factor [15] . We tested specimens for antibodies against 
Overall, we detected autoantibodies in 19 (30%) of the COVID-19 patients in our cohort using 209 manufacturer's thresholds (Table 1) . We did not find a statistically significant difference in the 
Although antiphospholipid syndrome is an emerging concern in COVID-19, we did not find 
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: