Which immunoglobulin class is known to produce anaphylactic reactions following blood transfusion?

The immunoglobulin class that is primarily associated with anaphylactic reactions, particularly in the context of blood transfusions, is IgE. This immunoglobulin is responsible for mediating hypersensitivity reactions, including anaphylaxis, by triggering mast cells and basophils to release histamine and other inflammatory mediators upon re-exposure to an allergen or antigen.

In the case of blood transfusions, if a patient has pre-existing antibodies (often due to previous exposure or sensitization), these antibodies can react with transfused materials that contain the respective antigens, leading to a severe allergic response. This process is particularly true for allergic reactions that are rapid and life-threatening, which is the hallmark of anaphylactic responses.

Given the context of IgE's role, it becomes clear why it is the correct answer when considering reactions associated with blood transfusions. IgM and IgG are involved in different types of immune responses and are more associated with delayed-type or acute hemolytic reactions rather than anaphylaxis. IgA is predominantly found in mucosal areas and secretions but does not typically play a role in the immediate hypersensitivity reactions seen in anaphylaxis related to blood transfusions.