Question

When temperatures drop below 30*C, IgM AIHA antibodies may bind RBCs and activate complement. This occurs particularly in the extremities, as the RBC IgM complexes return back to the core the temperature increases - causing IgM to dissociate and leave C3 behind (which gets inactivated by DAF / MIRL); opsonized cells are cleared by the spleen. However, extreme activation of complement can lead to intravascular hemolysis. What is the consequence of extreme activation of complement?

1) Intravascular hemolysis
2) Extravascular hemolysis
3) Decreased RBC production
4) Increased RBC production

Answer 1

Extreme activation of complement in type II hypersensitivity reactions, such as a hemolytic transfusion reaction, leads to intravascular hemolysis, which release hemoglobin into the bloodstream and can cause severe complications, including shock and organ failure.

Step-by-step explanation:

The question concerns the consequences of extreme activation of complement in the context of a type II hypersensitivity reaction. Specifically, the situation described involves immunoglobulin M (IgM) antibodies binding to red blood cells (RBCs) when temperatures drop, leading to complement activation. As the RBC-IgM complexes return to the body's core and temperature increases, IgM dissociates, leaving complement component 3 (C3) behind. When complement activation is extreme, it can cause a hemolytic transfusion reaction (HTR), which is a severe consequence where the intravascular hemolysis of RBCs occurs. This leads to a release of hemoglobin into the blood and potential obstruction of blood vessels, with the possibility of a systemic inflammatory response, shock, and multiple organ failure.