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Recurrent meningococcal infections associated with a functional deficiency of the C8 component of human complement
Abstract:
A patient is described who had a functional deficiency of the C8 complement component. His serum contained abnormal C8 which lacked some of the antigenic determinants of normal C8. The defect was associated with recurrent meningococcal infections due at different times to at least two strains. The patient's serum contained antibodies to meningococci and could induce phagocytosis and intracellular killing of the cocci by polymorphs. However, the serum was bactericidal only after the addition of C8-containing serum. As the patient did not give a history of susceptibility to other pyogenic organisms and has normal polymorph function, the circumstances of meningococcal infection must be unusual in that the plasma bactericidal activity critically determines the outcome: it may be that if large numbers of meningococci are not killed in the plasma, the polymorphs are overwhelmed.
Insights
A patient with a functional deficiency of the C8 complement component experienced recurrent meningococcal infections. This highlights the critical role of complement component 8 (C8) in combating Neisseria meningitidis.
Area of Science:
- Immunology
- Complement System Biology
Background:
- The complement system is crucial for innate immunity, aiding in pathogen clearance.
- Deficiencies in complement components can lead to increased susceptibility to infections, particularly from encapsulated bacteria.
Observation:
- A patient presented with recurrent infections caused by multiple strains of Neisseria meningitidis.
- The patient's serum exhibited a functional deficiency in the C8 complement component, with abnormal C8 lacking antigenic determinants.
- While the patient's serum could facilitate phagocytosis and intracellular killing by polymorphs, it lacked intrinsic bactericidal activity against meningococci.
Findings:
- The patient's serum demonstrated significantly reduced bactericidal activity against Neisseria meningitidis, which was restored upon the addition of normal C8-containing serum.
- The defect in C8 function was directly linked to the patient's susceptibility to meningococcal disease, despite normal polymorph function and antibodies to meningococci.
Implications:
- This case underscores the essential role of the terminal complement pathway, specifically C8, in effective host defense against Neisseria meningitidis.
- The findings suggest that plasma bactericidal activity is a critical determinant in managing meningococcal infections, potentially by preventing polymorph overload.