Complement-mediated enhancement of IgA-induced H2O2 release by human polymorphonuclear leucocytes

Area of Science:

• Immunology
• Microbiology

Background:

• Previous studies showed IgA opsonization of Staphylococcus aureus induces respiratory burst in human polymorphonuclear leucocytes (PMN).
• The role of complement in augmenting this IgA-mediated PMN response was not fully understood.

Purpose of the Study:

• To investigate the effect of complement opsonization on IgA-coated Staphylococcus aureus and its impact on PMN respiratory burst.
• To determine the specific complement pathway involved in this synergistic immune activation.

Main Methods:

• Heat-killed Staphylococcus aureus were opsonized with human serum IgA or secretory IgA (sIgA).
• Opsonized bacteria were subsequently treated with complement, with experiments conducted in the presence and absence of MgEGTA and using D-deficient serum.
• Hydrogen peroxide (H2O2) release from human PMN was measured to quantify the respiratory burst response.

Main Results:

• Complement opsonization of IgA-coated staphylococci resulted in at least a two-fold increase in specific H2O2 release by PMN compared to IgA alone.
• This cooperative effect was observed with complement activation via the alternative pathway, even in the presence of MgEGTA.
• The enhancement of H2O2 release was dependent on the initial amount of IgA used and occurred with both sIgA1 and sIgA2 subclasses.

Conclusions:

• Complement significantly enhances the IgA-mediated respiratory burst response of human PMN against Staphylococcus aureus.
• The alternative complement pathway plays a crucial role in this synergistic immune activation.
• This finding highlights the cooperative interaction between IgA and complement in bacterial opsonization and phagocyte activation.