Vaccination against meningococcus in complement‐deficient individuals

Inherited deficiency syndromes have been described for each of the component proteins and for many of the regulators of the complement system [1–3]. Although each of these syndromes is rare, increasing awareness has led to recent identification of many individual cases, as well as areas where one particular genetic defect is segregating in the population [4–6]. A useful subdivision of complement deficiencies is based upon the part of the pathway involved and the clinical syndrome produced [7]. The first group consists of individuals deficient in components of the classical activation pathway (C1, C4, C2) who most commonly present with immune complex disease which often resembles systemic lupus erythematosus. These individuals also have an increased susceptibility to bacterial infection, most commonly with encapsulated organisms such as Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae. The second group comprises those deficient in C3, including those in whom the deficiency is secondary to absence of a regulator such as factor H or factor I; they rarely develop immune complex disease but have a marked propensity to develop severe, recurrent bacterial infections, usually with the encapsulated organisms listed above. The third group, individuals deficient in components of the alternative pathway (factor D, factor B, properdin), show a particular susceptibility to infection with N. meningitidis. With the exception of properdin deficiency, all are very rare. The fourth group consists of individuals deficient in components of the terminal pathway (C5, C6, C7, C8, C9); these have a propensity to develop infections, frequently recurrent, with N. meningitidis and other organisms of the genus Neisseria.