Three different pathways of IgM-antibody-dependent hemolysis are mainly regulated by complement

Area of Science:

• Immunology
• Hematology

Background:

• Antibodies binding to red blood cells (RBCs) can cause hemolysis through Fc-mediated phagocytosis or complement activation.
• Complement activation on RBCs is detected by C3d-direct antiglobulin test (DAT), but it cannot differentiate hemolysis types or estimate severity.
• Autoimmune hemolytic anemia (AIHA), including cold agglutinin disease (CAD), involves autoantibodies that can trigger various hemolysis pathways.

Purpose of the Study:

• To investigate different types of hemolysis (extravascular, intravascular, eryptosis) in patients with CAD.
• To evaluate the utility of indirect tests for complement activity in conjunction with C3d-DAT.
• To determine the clinical significance of eryptosis in AIHA and CAD.

Main Methods:

• Analysis of sera from CAD patients under various conditions.
• Application of C3d-direct antiglobulin test (DAT).
• Utilizing indirect tests: free hemoglobin measurement and Annexin V-binding to phosphatidylserine-exposing RBCs.

Main Results:

• A positive C3d-DAT alone is insufficient to distinguish between extravascular hemolysis, intravascular hemolysis, and eryptosis.
• Indirect tests for complement activity, such as free hemoglobin and Annexin V-binding, are valuable additions to C3d-DAT.
• Eryptotic hemolysis can play a significant role in clinically relevant CAD and IgM warm AIHA.

Conclusions:

• Complement activation on RBCs can lead to diverse hemolytic mechanisms.
• Combining C3d-DAT with indirect hemolysis assays provides a more comprehensive assessment of RBC destruction.
• Considering eryptosis is crucial for effective treatment strategies in certain types of AIHA and CAD.