Deficiencies of the regulatory proteins properdin and Factor D, as well as of the terminal components of complement activation (C5–C9), are associated with an increase in susceptibility to Neisserial infections, reflecting the important role of cytolytic complement activity in the innate immune response against Neisseriae. Deficiencies of Factors H and I are associated with increased pyogenic infections (N. meningitidis, H. influenzae, and S. pneumoniae). The gene discussed is CFP; the disease is infection.