C9 and meningococcal infection: As a matter of fact, complement has a relevant role in preventing development of meningococcal disease, as evidenced by the increased incidence and recurrence of infection and disease in people with immune disorders related to FH [76, 77], or with congenital deficiencies in properdin or in one of the terminal complement components (C6, C7, C8, or C9) [76, 78, 79].