What are the functions of immunoglobulin M (IgM)?

IgM has several significant functions in the immune system. 

• As the first antibody the body produces after an infection, IgM plays a crucial role in mediating the initial non-specific immune response. 
• IgM is responsible for agglutination, cytolytic, and neutralization reactions, which help in fighting infections.  
• Its pentameric structure, which has 5 IgM molecules linked together, make it especially effective at binding and neutralizing antigens. 
• IgM activates the complement cascade as a series of proteins in the blood, which help in destroying microorganisms. 
• Predominantly found in the blood and lymph fluid, IgM is uniquely located to efficiently neutralize antigens in the early stages of the disease. Increased IgM levels may be a sign of recent infection or antigen exposure. 
• IgM plays an important role in triggering other parts of the immune system. It also stimulates the production of other types of antibodies such as IgG.
• IgM serves as a mediator of inflammation by contributing to the release of the anti-inflammatory cytokine IL-10 and clearing apoptotic debris after the cells in the body get a natural turnover.
• Intrauterine infection can be diagnosed by the presence of IgM in the fetus or newborn. Detection of IgM is also useful in diagnosing several congenital infections such as rubella, toxoplasmosis, HIV infection, syphilis, and cytomegalovirus infection. 
• IgM plays a role in homeostatic functions of healthy tissue.