CD55 and necrotizing enterocolitis: In this context, samples belonging to HI group had been collected from healthy full-term infants belonging to urbanized countries (n = 4255), while PI samples had originated from preterm newborns and critically ill infants affected by necrotizing enterocolitis (NEC) or CD55 deficiency with hyperactivation of complement, angiopathic thrombosis, and severe protein-losing enteropathy (CHAPLE syndrome) also belonging to urbanized countries (n = 5353).