Introduction: Acute Rheumatic Fever (ARF) is a serious post-infectious sequela of Group A Streptococcus (GAS) infection that can progress to rheumatic heart disease (RHD). Diagnosis relies on clinical features (Jones Criteria), with no definitive test available.
Methods: To assess the utility of autoantibodies as biomarkers a Human Protein-fragment Array (HPA) was designed based on antigens previously identified via high-content arrays and Phip-Seq, as well as historic autoantigens. This array, comprising 380 protein fragments on a Luminex bead system, was first applied to serum from the START (Searching for a Technology Driven ARF Test) Study comprising ARF (n=108) and matched controls (n=164); serious streptococcal infections, other inflammatory conditions, RHD, and healthy controls recruited in Australia and New Zealand (NZ).
Results: The HPA showed autoantibodies to several autoantigens were elevated in ARF, including historical antigens, supporting the bead-array approach. A novel autoantigen associated with protein transport was identified that was significantly elevated in ARF compared to all other groups (p<0.05, FC>1). Validation with sera from two NZ-based cohort studies (RFRISK and the GAS skin and throat study) confirmed significant antibody binding to this novel autoantigen in ARF (p<0.0001) compared with controls (AUC 0.825 as a single antigen). As elevated levels of total IgG3 had previously been associated with ARF, IgG3 reactivity was also measured using the HPA. ARF patients had elevated IgG3 reactivity against multiple autoantigens including historic and the novel autoantigen.
Conclusion: Collectively, this highlights the potential of autoantibodies as ARF biomarkers and underscores involvement of IgG3 in ARF pathogenesis.