APOH and autoimmune polyendocrinopathy: For several autoimmune disorders, including APS, gut bacteria that contain peptide sequence homologues to the epitopes of autoantigens have been identified, resulting in antigen cross-reactivity.4, 5, 6For instance, the gut commensalRoseburia intestinaliscontains peptide sequences homologous to the predominant B cell and T cell epitopes of β2GP-1.5Both APS patient plasma and a patient-derived monoclonal APLA indeed show cross-reactivity with this B cell epitope-mimicking bacterial protein.5Similarly, APS patient-derived T cells cross-react with theR.