Complement activation and attack on autologous cell membranes induced by streptolysin-O

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Streptolysin-O toxin creates channels in mammalian cell membranes.
• The mechanism by which this toxin interacts with the host immune system is not fully understood.

Purpose of the Study:

• To investigate the interaction between Streptolysin-O and human serum antibodies.
• To determine the effect of this interaction on the complement system.
• To elucidate the role of this interaction in host tissue damage and disease pathogenesis.

Main Methods:

• Incubation of Streptolysin-O with human serum containing immunoglobulin G (IgG) antibodies.
• Measurement of complement component consumption (C4, C5, C3) and hemolytic activity.
• Analysis of terminal complement complex (C5b-9) formation on target cell membranes.

Main Results:

• Streptolysin-O binds to human IgG antibodies, forming immune complexes.
• These complexes potently activate the complement cascade, leading to rapid consumption of C4 and C5, and significant C3 conversion.
• Complement activation occurs on target cell membranes where Streptolysin-O polymers have bound, leading to the formation of C5b-9 complexes.

Conclusions:

• Streptolysin-O-antibody complexes act as foci for potent, antibody-dependent complement activation.
• This process leads to self-attack on host cells, perpetuating tissue damage.
• The findings suggest a role for this mechanism in the pathogenesis of post-streptococcal diseases and immune evasion by bacteria.