Protection from Neisserial infection requires the ability to generate the MAC, which lyses these bacteria. Patients with inherited homozygous deficiency of C5, C6, C7, C8, and C9 are susceptible to recurrent meningococcal infections. In Japanese population, an inherited terminal complement component deficiency leads to about a 5,000-fold increase in the risk of Neisserial sepsis. Primary or secondary CD3 deficiency, which in turn reduces the ability to generate MAC, also results in increased susceptibility to meningococcal infection. Complement deficiency is not a risk factor in sporadic cases of meningococcal disease seen in the population at large.