C4A and autoimmune polyendocrinopathy: In 2016, Meroni et al. reported a case of a patient with APS and arterial thrombosis, where immunofluorescence revealed the presence of β2GPI IgG complexes and deposition of C1q, C4, and C3 on the thrombotic endothelium, findings indirectly consistent with activation of the classical complement pathway [59].