What happence when an antigen on a red blood cell comes in contact with the antibody designed to seek it out?

When an antigen on a red blood cell comes in contact with the antibody designed to seek it out, several events occur as part of the immune response:

1. Binding: The antibody, which has a specific shape that fits the antigen, binds to the antigen on the surface of the red blood cell. This binding reaction is highly specific, and each antibody only binds to its corresponding antigen.

2. Agglutination: Once the antibodies bind to the antigens on multiple red blood cells, they can cause the red blood cells to clump together, forming visible aggregates called agglutination. This happens because the antibodies act as bridges between the red blood cells, linking them together.

3. Complement activation: The binding of antibodies to antigens on the red blood cell surface can activate the complement system, which is a part of the immune response that helps destroy pathogens and foreign substances. Activation of the complement system leads to the formation of a membrane attack complex, which creates pores in the red blood cell membrane, causing cell lysis (destruction).

4. Phagocytosis: After agglutination and complement activation, the antibody-coated red blood cells are recognized and engulfed by phagocytic cells, such as macrophages and neutrophils. Phagocytes engulf and digest the red blood cells, removing them from circulation.

5. Clearance: The destruction of red blood cells leads to the release of hemoglobin, which is broken down and processed by the liver and spleen. The remnants of the red blood cells are cleared from the body.

These immune responses collectively contribute to the body's defense mechanisms against foreign invaders and help maintain healthy blood composition.