What are the infectious manifestations of homozygous complement deficient states?
The complement deficiencies can be divided into those of the classical pathway (C1–C9), alternative complement pathway (factors B, D, and P), the mannose-binding lectin (MBL) pathway and their associated proteases (MASP-1 and MASP-2), and the complement regulatory proteins (C1INH, factor H, factor I, MCP). Deficiency of C3 or MBL is associated with recurrent blood-borne infections with encapsulated bacteria including S. pneumoniae and H. influenza . Deficiencies of components of the membrane attack complex (C5–C9) or alternative complement pathway factors are associated with recurrent Neisseria infections, (both N. meningitidis and N. gonorrhoeae ). C6 deficiency is most common. Patients with recurrent bouts of Neisserial infections, particularly when systemic, should be evaluated for the presence of a complement deficiency. All patients should be immunized with the conjugate meningococcal vaccine. Use of prophylactic antibiotics is controversial due to the risk of causing antibiotic resistant strains of Neisseria .
