Immunodeficiency due to a late component of complement deficiency

Immunodeficiency due to a late component of complement deficiency refers to a group of inherited immune disorders caused by deficiencies in the terminal components of the complement system, specifically C5, C6, C7, C8, or C9. The complement system is a critical part of the innate immune defense, and the late (terminal) components are responsible for forming the membrane attack complex (MAC), which directly kills certain bacteria by creating pores in their cell membranes. When any of these late components are missing or dysfunctional, the body loses its ability to effectively lyse encapsulated bacteria, particularly Neisseria species (such as Neisseria meningitidis and Neisseria gonorrhoeae). Patients with late complement component deficiencies are highly susceptible to recurrent, severe, and sometimes life-threatening meningococcal infections, including meningitis and meningococcal septicemia. These infections may occur at an older age than typically seen in the general population and tend to recur. Some patients may also experience disseminated gonococcal infections. Notably, while susceptibility to Neisseria infections is markedly increased, patients generally do not have the broad susceptibility to infections seen in other primary immunodeficiencies. C9 deficiency tends to be the mildest form, as the MAC can still partially form without C9, though its bactericidal efficiency is reduced. Management focuses on prevention and early treatment of infections. Vaccination against Neisseria meningitidis (including meningococcal conjugate and serogroup B vaccines) is strongly recommended, though vaccine responses may be suboptimal due to the complement deficiency. Prophylactic antibiotics may be considered in some patients, particularly those with a history of recurrent infections. Prompt antibiotic treatment of acute infections is essential. Genetic counseling is recommended for affected families. There is currently no replacement therapy available for complement components, and treatment remains primarily supportive and preventive.

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