Harr Immunology, Serology & Blood Bank (ISBB) 2026 – 400 Free Practice Questions to Pass the Exam

In cases of immediate hemolytic transfusion reactions, the antibodies primarily involved are IgM. This type of reaction typically occurs due to the transfusion of ABO-incompatible blood, where the recipient has pre-existing IgM antibodies against the ABO antigens on the donor red blood cells.

IgM is a pentameric immunoglobulin, meaning it has five basic units linked together, which gives it a high avidity for antigens. This structural characteristic allows IgM to efficiently cross-link antigens on the surface of red blood cells, leading to their rapid agglutination and subsequent destruction (hemolysis) by the immune system. Such reactions can start almost immediately after transfusion begins, hence the term "immediate."

While other classes of antibodies serve important roles in the immune response, they are not typically implicated in immediate hemolytic transfusion reactions. IgG, for example, is more commonly associated with delayed hemolytic reactions, where sensitization to blood group antigens occurs over time rather than instantaneously. IgA is primarily found in mucosal areas and does not play a significant role in blood transfusion reactions. IgE is associated with allergic responses and does not typically mediate hemolytic reactions. Thus,