Abstract
Objectives: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19) and the outbreak of COVID-19 was reported in December 2019 in Wuhan, China. Serological test is conducted to discriminate prior infection of SARS-CoV-2. The influence of auto-antibodies on the results of anti-SARS-CoV-2 antibodies was investigated in a few studies. Here, we investigated whether the results of anti-SARS-CoV-2 antibodies would be modified in patients with rheumatoid arthritis (RA). Methods: Patients with RA were recruited at Sagamihara National Hospital from July 2014 to October 2015 (n=38, 2014 cohort) and at Tokyo National Hospital from June to October 2020 (n=93, 2020 cohort). Anti-SARS-CoV-2 antibodies were measured in collected sera from these RA patients by electrochemiluminescence immunoassay (ECLIA) or immunochromatographic assay (ICA). Results: Anti-SARS-CoV-2 antibodies were not detected in all the samples form RA patients in both cohorts by the ECLIA. However, anti-SARS-CoV-2 antibodies were detected in the serum samples from three (7.9%) in 2014 cohort by the ICA and fifteen (16.1%) in 2020 cohort. The IgM rheumatoid factor levels were increased in RA patients with IgM anti-SARS-CoV-2 antibodies by ICA compared with RA without any anti-SARS-CoV-2 antibodies (mean ± standard deviation [IU/ml], 1223.0 ± 1308.7 vs. 503.6 ± 1947.2, P=0.0101). The levels of IgG rheumatoid factor were also upregulated in RA patients with IgM anti-SARS-CoV-2 antibodies by ICA (4.0 ± 0.7 vs. 2.4 ± 0.9, P=0.0013). Conclusion: The results of IgM anti-SARS-CoV-2 antibody by the ICA would be modified by IgM or IgG rheumatoid factors in RA patients.
IgG Rheumatoid Factor in Synovial Fluid of Patients with Rheumatoid Arthritis.
