Chronic low-grade inflammation and innate immune system overactivation are now recognized causes of type 2 diabetes mellitus and MetS.4,5 In particular, the alternative pathway (AP) has received attention for its potential causal role in cardiometabolic disease.6 AP activation requires CFB (complement factor B) to bind C3 to form C3B, which opsonises pathogens and contributes to the formation of the membrane attack complex.6 Thus, CFB is fundamental to pathogen clearance and host cell apoptosis. Here, C3 is linked to type 2 diabetes mellitus.