American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What is the role of IgM in the immune response?

1. Produced later during the immune response

2. First to increase in immune response

3. Involved in mucosal immunity

4. Triggers allergic reactions

The correct answer is: First to increase in immune response

IgM plays a crucial role in the immune response as the first antibody produced in response to an antigen. When the body encounters a pathogen, it initiates a primary immune response, during which IgM is synthesized and released by B cells. This antibody is particularly effective because it can form multimers (pentamers), allowing it to effectively bind to multiple antigens and activate complement pathways, enhancing the immune response. The early rise of IgM is essential for providing initial protection against infections while the body ramps up the production of other antibodies, like IgG, that are produced later in the immune response. This transition signifies the body’s adaptive immune response, where the immune system becomes more specific and effective. In terms of the other choices, IgM is not produced later in the immune response; rather, it is the first to respond. It is also not specifically involved in mucosal immunity, as that role is more often attributed to IgA. Lastly, while IgM does participate in immune responses, it is not associated with triggering allergic reactions, a role more associated with other immunoglobulins, particularly IgE.