More than one choice may apply.
Which of the following antibody capabilities causes a transfusion reaction with A or B erythrocyte antigens?
a. Neutralization
b. Precipitation
c. Complement fixation
d. Agglutination

Antibodies are proteins produced by the immune system that recognize and bind to specific antigens, such as those found on the surface of erythrocytes (red blood cells). Their primary functions include neutralization of pathogens, agglutination of cells, and activation of the complement system, which can lead to cell lysis.

Agglutination is the process by which antibodies bind to multiple antigens on the surface of cells, causing them to clump together. This is a critical mechanism in transfusion reactions, as antibodies against A or B antigens can agglutinate erythrocytes that possess these antigens, leading to potentially severe immune responses.

Complement fixation refers to the process where antibodies bound to antigens activate the complement system, a series of proteins that enhance the immune response. This can lead to the lysis of cells, including erythrocytes in transfusion reactions, but is distinct from agglutination, which is primarily responsible for the clumping of cells.