Deficiency of the eighth component of complement. Evidence for linkage of C8 alpha-gamma pattern with C8 beta deficiency in sera of twelve patients

Definition of a new score for severity of generalized Neisseria meningitidis infection

Neisseria meningitidis infection may present as meningitis or as severe, fulminant sepsis. In order to classify individual patients early according to the expected course of the disease, we developed a score named Neisseria sepsis index [NESI]. The NESI was defined using the parameters heart rate, mean arterial blood pressure, base excess and presence of acute subcutaneous bleeding and/or skin necroses (minimal value [= no evidence for sepsis] NESI 0; maximum value [= most severe sepsis] NESI 8). Seventeen patients with documented, systemic N. meningitidis infection were prospectively assessed for the terminal complement complex (TCC), serum tumour necrosis factor alpha (TNF alpha) levels (as laboratory parameters for severity of sepsis) and NESI score. The evaluation was immediately performed when the patients were admitted to the hospital. The 17 patients showed the following distribution of data: NESI 0 (n = 4), NESI 1 (n = 6), NESI 2 (n = 0), NESI 3 (n = 1), NESI 4 (n = 2), NESI 5 (n = 2), NESI 6 (n = 0), NESI 7 (n = 1), NESI 8 (n = 1). Mortality was 4/17 patients, all had NESI > or = 5. TCC values ranged from 647-6461 ng/ml (normal range: 130-360 ng/ml); and was not correlated to NESI. TNF alpha values ranged from 10-910 pg/ml and were correlated to NESI (r2 = 0.71, n = 17, P < 0.001). In patients with fatal outcome, TNF alpha was 600 +/- 160 pg/ml (mean +/- SEM) and in surviving patients 130 +/- 50 pg/ml (mean +/- SEM). TNF alpha was increased in 15/17 patients when compared to normal controls (< 27 pg/ml). CONCLUSION. The NESI is based on few clinical, objective data, that are available in every hospital. NESI appears to offer an instrument: (1) for making decisions in regard to appropriate monitoring and treatment of vital organ function; and (2) for assessing the quality of care for this life-threatening infection.

Infectious diseases associated with complement deficiencies

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.

Prevalence of hereditary properdin, C7 and C8 deficiencies in patients with meningococcal infections

High incidence of hereditary complement (C) deficiencies was found among 101 patients who had a meningococcal disease. This study revealed 11 non-related patients with complete C deficiency: five deficient in C7, three in C8, two in properdin and one in C2. Additional C-deficient individuals, most of them with no history of severe bacterial infections, were detected in family studies. The C8-deficient patients were found to have a selective deficiency of the C8-beta subunit and a reduced expression of the alpha/gamma subunit. Only a few families with properdin deficiency have been described so far. However, it is likely that frequent analysis of the activity of the alternative C pathway in survivors of severe bacterial infections will disclose numerous properdin-deficient patients. All our C7-, C8- and properdin-deficient patients are Sephardic Jews whose families originated from Morocco, Yemen (C7 and C8 deficient) or Tunisia (properdin deficient). This and other findings indicate that the type of complement abnormality found in association with meningococcal infections varies with the ethnic origin of the patient.