Complement Factor H Serum Levels Determine Resistance to Pneumococcal Invasive Disease

Area of Science:

• Immunology
• Microbiology
• Genetics

Background:

• Streptococcus pneumoniae causes severe infections, with complement system activation crucial for bacterial clearance.
• The alternative pathway amplifies complement activation but is regulated by complement factor H (FH).
• Variability in human FH levels may influence host defense against pneumococcal disease.

Purpose of the Study:

• To investigate the impact of variable human serum FH levels on host defense against Streptococcus pneumoniae.
• To elucidate the role of FH in regulating alternative pathway activity during pneumococcal infections.

Main Methods:

• Utilized an in vivo mouse model of pneumococcal infection.
• Conducted in vitro human serum assays to assess opsonophagocytic killing.
• Correlated serum FH levels with the efficacy of bacterial clearance.

Main Results:

• Serum FH levels directly correlate with the effectiveness of opsonophagocytic killing of Streptococcus pneumoniae.
• Lower FH levels were associated with reduced bacterial clearance, indicating impaired host defense.
• FH levels were found to modulate alternative pathway activity, influencing resistance to invasive disease.

Conclusions:

• Naturally occurring variations in human serum FH levels significantly affect resistance to invasive pneumococcal disease.
• FH plays a critical, previously unrecognized role in host defense by balancing alternative pathway activity.
• FH levels represent a key determinant of susceptibility to severe pneumococcal infections.