Complement in pneumococcal infections with varying degrees of severity

Area of Science:

• Immunology
• Infectious Diseases
• Biochemistry

Background:

• Complement system plays a crucial role in innate immunity against bacterial infections.
• Pneumococcal infections can trigger complex immune responses, including complement activation.
• Understanding complement profiles in different severities of pneumococcal disease is vital for prognosis.

Purpose of the Study:

• To investigate complement component and C1 subcomponent complex levels in adults with varying severities of pneumococcal infections.
• To correlate complement alterations with disease severity and specific clinical manifestations.
• To explore the involvement of different complement pathways in pneumococcal pathogenesis.

Main Methods:

• Measurement of complement components (C1q, C1s, C4, C3, factor B, properdin) and C1 subcomponent complexes in 16 adult patients.
• Categorization of patients based on disease severity (fulminant, pneumonia, meningitis, otitis).
• Comparative analysis of complement profiles across different clinical presentations.

Main Results:

• Pronounced hypocomplementemia observed in patients with fulminant pneumococcal disease and septic shock.
• Elevated C1-r-C1-s-C1- IA complexes in pneumonia and meningitis suggest C1 activation, despite normal C1q, C1s, C4, and C3 levels.
• Moderately decreased properdin levels indicate alternative pathway involvement in some cases.
• No significant changes in complement profile were found in adults with pneumococcal otitis.

Conclusions:

• Complement system dysregulation is associated with pneumococcal infection severity.
• Specific complement activation patterns, particularly of C1, are evident in severe respiratory and central nervous system pneumococcal infections.
• Adult pneumococcal otitis does not significantly alter the systemic complement profile, contrasting with findings in children.