Correlation of natural autoantibodies and cardiovascular disease‐related anti‐bacterial antibodies in pericardial fluid of cardiac surgery patients

Summary Our previous studies showed that anti‐citrate synthase (anti‐CS) immunoglobulin (Ig)M natural autoantibodies are present in healthy individuals without previous antigen stimulation, but no studies have investigated their presence in the pericardial fluid (PF). Therefore, we detected the natural anti‐CS IgG/M autoantibody levels in plasma and PF of cardiac surgery patients and investigated their relationship with cardiovascular disease‐associated bacterial pathogens. PF and blood samples of 22 coronary artery bypass graft (CABG) and 10 aortic valve replacement (AVR) patients were tested for total Ig levels, natural autoantibodies and infection‐related antibodies using enzyme‐linked immunosorbent assay (ELISA) and Luminex methods. The B cell subsets were measured by flow cytometry. The total Ig subclass levels were four to eight times lower in PF than in plasma, but the natural anti‐CS IgM autoantibodies showed a relative increase in PF. The frequency of CD19 + B lymphocytes was significantly lower in PF than in blood ( P  = 0·01), with a significant relative increase of B1 cells ( P  = 0·005). Mycoplasma pneumoniae antibody‐positive patients had significantly higher anti‐CS IgM levels. In CABG patients we found a correlation between anti‐CS IgG levels and M. pneumoniae, Chlamydia pneumoniae and Borrelia burgdorferi antibody titres. Our results provide the first evidence that natural autoantibodies are present in the PF, and they show a significant correlation with certain anti‐bacterial antibody titres in a disease‐specific manner.