Cross-reaction of SARS-CoV antigen with autoantibodies in autoimmune diseases

To investigate the significance of the SARS-associated coronavirus (SARS-CoV) antibody, detected by ELISA and indirect immunofluorescence assays (IFA) for the SARS-CoV Vero E6 cell lysates, in non-SARS subjects, 114 serum samples from healthy controls and 104 serum specimens from autoimmune disease patients were collected. The results of ELISA showed that among 114 sera from healthy controls, 4 (3.5%) were positive of SARS-CoV-IgG antibody and 114 (100%) were all negative of SARS-CoV-IgM antibody; the specificity of SARS-CoV-IgG antibody for SARS patients was 96.5%, but the specificity of both SARS-CoV-IgG and -IgM antibodies for SARS patients was 100%. In 58 cases with SLE, positive rates of SARS-CoV-IgG and -IgM antibodies were 32.8% (19/58) and 8.6% (5/58), respectively, in which 11 cases (19%) were positive of both SARS-CoV-IgG and -IgM antibodies; in 10 cases with SS, positive rate of both SARS-CoV-IgG and -IgM antibodies was 10% (1/10); in 16 cases with MCTD, positive rate of SARS-CoV-IgG was 37.5% (6/16), positive rate of both SARS-CoV-IgG and -IgM antibodies was 6.3% (1/16); in 20 cases with RA, one case was positive (5%) of SARS-CoV-IgG. However, of all samples with positive SARS-CoV-IgG and -IgM antibodies for autoimmune diseases and healthy controls, SARS-CoV RNA and antibodies were all negative by RT-PCR and IFA. All sera for negative or positive ELISA results were also negative or positive results using ELISA with Vero E6 cells lysates. These studies showed that SARS-CoV Vero E6 cell lysates for the ELISA to detect SARS-CoV antibodies could lead to the false-positive reactions or cross-reactions of SARS-CoV antibodies in non-SARS diseases and healthy controls, and the false-positive reactions or cross-reactions were related to Vero E6 cell lysates and autoantibodies in non-SARS population.