Which clinical history findings are characteristic of defects in cell lysis causing complement deficiencies?

Updated: Apr 28, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Michael A Kaliner, MD  more...
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Complement deficiencies of the terminal cascade proteins also predispose patients to infection, but the clinical history of these patients is different. The terminal complement proteins are the proteins in the cascade that form the MAC, ie, complement proteins C5-C9. These proteins are responsible for bactericidal killing of organisms such as N meningitidis. The frequency rate of meningococcal infection in patients with terminal complement deficiency is as high as 66%. In addition to this high rate of first-time infection, the frequency rate of recurrence with the same organism is also as high as 50%. The serogroups of N meningitidis responsible for infections in this group tend to be the more rare serogroups Y and W135, rather than the more common serogroups B, A, and C.

Clinically, patients with terminal deficiency tend to present with infection at an older age compared with patients with other complement deficiencies. These individuals also have less morbidity and mortality associated with infection. Unlike patients with a classic pathway deficiency, humoral immunity is intact but lysis of pathogenic organisms is impaired.

Both the opsonization and lytic function of complement protect against a variety of other nonbacterial pathogens, such fungi, viruses, and mycobacteria. The role of complement in defense against viral infection is sufficiently important that pathogenic viruses have had to develop strategies to evade complement activation. For example, human immunodeficiency virus type 1 has recently been described as escaping complement-mediated lysis through the incorporation of regulatory proteins, such as DAF, into the viral envelope. Similarly, other viruses have also evolved complement-specific means of escape.

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