Which antibodies are known to bind complement?

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Multiple Choice

Which antibodies are known to bind complement?

The key idea is that some antibody–antigen interactions activate the complement system, leading to hemolysis that can occur inside blood vessels. Antibodies that are efficient at fixing complement are typically those that can strongly engage C1q when they bind their RBC antigen. IgM antibodies are particularly good at this due to their pentameric structure, so antibodies against ABO antigens are classic complement fixers and can cause rapid intravascular hemolysis if an incompatible transfusion occurs. Beyond ABO, several other antibody systems can also activate complement. Lewis antibodies are often IgM and can fix complement, contributing to complement-mediated reactions. Kidd antibodies (anti-Jka, anti-Jkb) are known for their ability to activate complement as well, which can enhance hemolysis and complicate transfusion. Antibodies to I and P antigens can also bind complement when they attach to their targets on RBCs, enabling classical pathway activation. Kell antibodies, by contrast, are usually IgG and tend to cause hemolysis mainly via opsonization and extravascular clearance rather than robust intravascular hemolysis through complement activation. That’s why they’re less described as complement-binding antibodies. So, antibodies that are known to bind complement include those in the ABO, Lewis, Kidd, I, and P systems.

The key idea is that some antibody–antigen interactions activate the complement system, leading to hemolysis that can occur inside blood vessels. Antibodies that are efficient at fixing complement are typically those that can strongly engage C1q when they bind their RBC antigen. IgM antibodies are particularly good at this due to their pentameric structure, so antibodies against ABO antigens are classic complement fixers and can cause rapid intravascular hemolysis if an incompatible transfusion occurs.

Beyond ABO, several other antibody systems can also activate complement. Lewis antibodies are often IgM and can fix complement, contributing to complement-mediated reactions. Kidd antibodies (anti-Jka, anti-Jkb) are known for their ability to activate complement as well, which can enhance hemolysis and complicate transfusion. Antibodies to I and P antigens can also bind complement when they attach to their targets on RBCs, enabling classical pathway activation.

Kell antibodies, by contrast, are usually IgG and tend to cause hemolysis mainly via opsonization and extravascular clearance rather than robust intravascular hemolysis through complement activation. That’s why they’re less described as complement-binding antibodies.

So, antibodies that are known to bind complement include those in the ABO, Lewis, Kidd, I, and P systems.

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