Influence of a deficiency of the second component of complement on the bactericidal activity of neutrophils in vitro

Area of Science:

• Immunology
• Microbiology
• Complement System

Background:

• The second component of complement (C2) plays a crucial role in the immune response.
• Polymorphonuclear leukocytes (PMN) are key phagocytic cells in bacterial killing.
• Deficiencies in complement components can impair host defense against infections.

Purpose of the Study:

• To investigate the role of C2 in the opsonophagocytic killing of Staphylococcus aureus by human PMN.
• To determine the impact of C2 deficiency on PMN function in vitro.
• To assess the contribution of cell-associated C2 to bacterial clearance.

Main Methods:

• Utilized serum from C2-deficient patients and healthy controls.
• Assayed the killing of Staphylococcus aureus (502A) by PMN in vitro under various opsonization conditions.
• Investigated the effect of C2 reagent addition and serum heating on bacterial killing.
• Examined the role of PMN washing on bacterial clearance.

Main Results:

• C2-deficient serum resulted in suboptimal killing of S. aureus by PMN.
• Addition of C2 reagent or heat-stable opsonins corrected the defective bacterial killing.
• Twice-washed control PMN showed enhanced S. aureus killing compared to patient PMN, attributed to residual C2.
• Progressive washing of control PMN reduced their staphylocidal effectiveness.
• PMN from both C2-deficient patients and controls effectively killed Escherichia coli in C2-deficient serum.

Conclusions:

• A complete, selective deficiency of C2 impairs the optimal killing of Staphylococcus aureus by PMN.
• C2 is essential for efficient opsonization and subsequent phagocytosis and killing of S. aureus.
• Cell-associated C2 on PMN contributes to bacterial clearance, particularly under suboptimal opsonization conditions.
• The complement system's role in bacterial killing may vary depending on the bacterial species.