How can autoimmune reactions reduce red blood cell counts?

Autoimmune reactions can reduce red blood cell counts through a process known as autoimmune hemolytic anemia. In this condition, the body’s immune system mistakenly produces autoantibodies that target and bind to the individual's own red blood cells.123

This binding leads to a reduction in red blood cell counts through two primary mechanisms:

• Phagocytosis: Red blood cells coated with these antibodies are recognized by the spleen and other reticuloendothelial cells. These cells ingest and destroy the antibody-coated red blood cells, a process called phagocytosis.12
• Complement Activation: The binding of autoantibodies to the surface of red blood cells can activate the complement system—a series of plasma proteins—which directly causes the lysis (bursting) of the red blood cells.23

Because the rate of destruction exceeds the bone marrow's ability to produce new cells, the total count of circulating red blood cells drops, resulting in anemia.14