How is mechanism of cold agglutinin disease?

Being a strong complement activator, antigen-bound IgM-CA on the cell surface binds C1 and thereby initiates the classical complement pathway. ➢ C1 esterase activates C4 and C2, generating C3 convertase, which results in the cleavage of C3 to C3a and C3b ➢ Upon returning to central parts of the body with a temperature of 37°C, IgM-CA detaches from the cell surface, allowing agglutinated erythrocytes to separate from each other, while C3b remains bound. ➢ Activation of complement components C1 through C3 results in covalent binding of C3b to the red cell membrane and renders circulating red cells susceptible to phagocytosis