Results
There were 116 patient samples tested; 32 from group 1 (acute, non-COVID-19, ITU) 25 from group 2 (acute, COVID-19, ITU), 35 from group 3 (convalescent, COVID-19, post ITU) and 24 from group 4 (convalescent, COVID-19, non-hospitalised). The demographic descriptions inTable 1 find a female preponderance and slightly younger cohort in the non-hospitalised convalescent group. The average time from symptom onset was longer in the post ITU patients (151 days) than the non-hospitalised convalescent cohort (38 days). Non-white ethnicity is higher in all the COVID groups than the non-COVID ITU cohort, in keeping with known risk factors for severe COVID [14]. The details of number of samples tested are described in Table 2 ; for some patients there was insufficient sample to run all tests.
The number of autoantibodies varied between groups. The highest numbers of autoantibodies to different antigenic targets was detected in the severe COVID disease groups. In group 1 (acute Non COVID-19, ITU) 13/32 (41%) individuals had autoantibodies; 8 tested positive for 1 autoantibody, 4 for 2 autoantibodies and 1 for 3. For group 2 (acute COVID-19, ITU) 15/25 (60%) individuals had autoantibodies; 12 tested positive for 1 autoantibody, 1 for 2 autoantibodies and 2 for 3. In group 3 (convalescent COVID-19, post ITU) 27/36 (75%) individuals had autoantibodies, 14 tested positive for 1 autoantibody, 10 for 2 autoantibodies and 3 for 3. In group 4 (convalescent, COVID-19, non-hospitalised) 13/24 (54%) individuals had autoantibodies and none tested positive for more than one (Figure 1 ).
Representative slides of epidermal, skeletal, cardiac and smooth muscle autoantibodies are shown in Figure 2 . In the acute Non COVID-19, ITU patients there were many different causes of their illness (Supplementary Table 1) and autoantibodies were found against nearly all (12/13) of the different autoantigens examined, indicating a more random distribution. A higher proportion of acute COVID-19, ITU patients had autoantibodies (60% versus 41%) but to a narrower range of autoantigens (7/13) with a preponderance of epidermal (41%) and skeletal antibodies (17%). This preponderance was seen in convalescent, COVID-19, post ITU with epidermal (19%) and skeletal antibodies (19%) but additionally cardiac muscle antibodies (28%) and smooth muscle antibodies (31%). Representative slides of epidermal, smooth muscle, skeletal muscle and cardiac muscle autoantibodies are shown in