CD40LG and rheumatoid arthritis: When using IFX treated-RA patients as SARS-CoV-2 serology negative controls (patients n=7, samples n=8) (Figure 2), unspecific signal was detected for IgM in seven assays (test D: 1/8; test E: 1/8; test F:1/8 test I: 3/8; test N: 2/8; test O: 4/6; and test P: 3/6) and for IgG (Figure 3) in two assays (test B: borderline positive signal in 2/2 samples and test P: 3 of 6 samples).