What is the primary function of IgM in the immune response?

The primary function of IgM in the immune response is indeed to be very effective in killing bacteria. IgM is the first antibody produced in response to an infection, and it plays a crucial role in the early stages of the immune response. This immunoglobulin is particularly effective due to its pentameric form, which allows it to bind multiple antigens simultaneously. This high avidity enables IgM to effectively agglutinate (clump together) pathogens, making it easier for other immune cells to locate and eliminate them. Additionally, IgM activates the complement system, which further enhances its ability to kill bacteria through lysis and opsonization.

In contrast, while other immunoglobulins may manage different roles in the immune response — such as regulating B cell activity or carrying out antiviral actions — the specific and immediate response to bacterial presence is a defining characteristic of IgM's role. This highlights its importance as the first line of defense against pathogens during the initial immune response.