A novel method for direct measurement of complement convertases activity in human serum

Area of Science:

• Immunology
• Biochemistry
• Clinical Diagnostics

Background:

• Complement convertases are crucial for complement cascade amplification.
• Defective complement function is implicated in infections, kidney disease, autoimmune disorders, and ischemia-reperfusion injury.
• Current assays for convertase function use non-physiological conditions with purified components.

Purpose of the Study:

• To develop and validate a novel assay for direct measurement of complement convertase activity in patient sera.
• To enable the study of complement cascade phases separately under near-physiological conditions.
• To facilitate screening for factors affecting convertase stability and function.

Main Methods:

• A new assay was designed using C5 blocking compounds to separate the complement cascade into two phases.
• Rabbit erythrocytes or antibody-sensitized sheep erythrocytes were used as platforms for convertase formation.
• Haemolysis was measured to quantify convertase activity and membrane attack complex formation.

Main Results:

• The assay allows for direct measurement of convertase activity and membrane attack complex formation in patient sera.
• The assay can identify host factors like C3 nephritic factor and anti-complement autoantibodies.
• The assay can detect gain-of-function mutations affecting complement convertase half-life.

Conclusions:

• A novel, validated assay enables direct assessment of complement convertase activity in patient sera.
• This assay provides a more physiological approach to studying complement function and diagnosing related diseases.
• The assay facilitates the identification of novel therapeutic targets and diagnostic biomarkers for complement-mediated disorders.