What is Immunoglobulin M (IgM)?

Immunoglobulin M (IgM) is a type of antibody found in the blood and lymph fluid. It is the first antibody that the immune system produces in response to an infection and constitutes a critical aspect of the initial, nonspecific immune response. IgM plays a pivotal role in the immune system, particularly in restricting the spread of infections in the early stages.