Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibody isotypes in systemic lupus erythematosus patients prior to vaccination: associations with disease activity, anti-nuclear antibodies, and ongoing pharmacotherapy during the first year of the pandemic

Objectives: The impact of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic on Swedish individuals with arthritis was recently presented (1) but less is known regarding other rheumatic diseases, e.g. systemic lupus erythematosus (SLE). Similarly to SLE, severe SARS-CoV-2 infection includes risks for thromboembolism, an unbalanced type I interferon response, and activation of the complement system. Herein, SARS-CoV-2 antibodies from patients collected before vaccination were detected and related to SLE progression and anti-nuclear antibody levels. Methods: We included 100 patients (83 women, 17 men) with established SLE (mean duration 15 years) who had a regular physical visit to the rheumatology unit in Linkoping from March 2020 to January 2021. All subjects donated blood at their visit during the pandemic and had done likewise before the pandemic. SARS-CoV-2 antibody isotypes [immunoglobulin (Ig)G, IgA, IgM] to the cell-receptor binding S1 spike outer envelope protein were detected by enzyme-linked immunosorbent assay. IgG anti-nuclear antibody specificities were measured by addressable laser bead immunoassay. Results: SARS-CoV-2 antibodies of at least one isotype were found in 36% of patients;IgA was the most common (30%), followed by IgM (9%) and IgG (8%). Plasma albumin (p = 0.04) and anti-double-stranded (anti-dsDNA) (p = 0.003) levels were lower in SARS-CoV-2 antibody-positive than in negative cases. A tendency for lower SLEDAI-2K among SARS-CoV-2 antibody-positive individuals was observed (p = 0.06). Body mass index, smoking habits, complement (C3, C4) levels, daily glucocorticoid dose, hydroxychloroquine (HCQ), and self-reported coronavirus disease 2019 (COVID-19) symptoms were not associated with SARS-CoV-2 antibodies. Conclusions: Our data from early 2021 show that a large proportion of Swedish SLE patients had serological signs of exposure to SARS-CoV-2, but apparently with a minor impact on the SLE course. The presence of SARS-CoV-2 antibodies was associated with lower anti-dsDNA levels, possibly indicating that the subgroup with higher anti-dsDNA levels had been more careful with their social contacts or to a higher extent were prescribed immunosuppressive drugs affecting immunoglobulin formation. However, the use of steroids and HCQ had no distinct effects, and self-reported COVID-related symptoms correlated poorly with all isotypes.