Binding specificity of IgG antibodies to mycobacterial DNA in plasmas of patients with tuberculosis and healthy controls.

Anti-DNA antibodies are a diverse set of antibodies that bind to structures on DNA that vary with clinical setting. In systemic lupus erythematosus (SLE), anti-DNA antibodies interact with the B-DNA backbone, binding DNA irrespective of species origin. In contrast, in the sera of otherwise healthy individuals (normal human subjects [NHSs]), anti-DNA antibodies bind to certain bacterial DNA. Furthermore, sera from patients with SLE and NHS controls can bind to the left-handed Z-DNA conformation. In the current studies, we have explored the antibody response to mycobacterial DNA from patients with tuberculosis (TB) and NHSs, focusing on DNA from Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis bacillus Calmette-Guérin (BCG), given their high GC content and predicted capacity to form Z-DNA. Using ELISAs, we demonstrated that plasmas from patients with TB and NHSs contain antibodies to mycobacterial DNA, with a greater response to Mtb DNA than BCG DNA. To elucidate these findings, we conducted an in silico analysis with Z-Hunt-III, synteny analysis, and an in-house R Shiny program, Z-GENIE, to identify Z-DNA-forming sequences (ZFSs) and genomic regions that may be antigenic. Our analysis suggested that regions of difference and single-nucleotide polymorphism-generated ZFSs may contribute to sequence differences, which may influence antigenicity. Additionally, we provide evidence that shared sequences between DNA of Mtb and nontuberculous mycobacteria could explain the observed pattern of antibody reactivity. Together, these findings suggest that anti-DNA antibodies from patients with TB and NHS controls can distinguish between the DNA of different mycobacterial species and could serve as serological markers for infection or exposure.