Which immunoglobulin class is most commonly involved in transfusion reactions?

The most commonly involved immunoglobulin class in transfusion reactions is IgG. This is primarily due to its ability to cross the placenta and its role in secondary immune responses. IgG antibodies are known to recognize specific antigens on red blood cells, which can occur during a blood transfusion if the recipient has developed antibodies against these antigens from prior sensitization.

When IgG binds to its target antigen on transfused red blood cells, it can activate the complement system and lead to hemolysis, which is a significant mechanism of transfusion reactions. Unlike IgM, which is involved in primary immune responses and is effective at agglutination, its large pentameric structure typically cannot pass through the vascular endothelium, thus limiting its role in transfusion reactions compared to IgG. Additionally, IgE is associated with allergic reactions and not typically with transfusion reactions, and IgA is more relevant in mucosal immunity.

Therefore, IgG's characteristics of promoting opsonization and activating complement make it the predominant antibody class implicated in adverse transfusion reactions.