What is the first antibody formed after exposure to an antigen?

The first antibody formed after exposure to an antigen is IgM. This immunoglobulin plays a crucial role during the initial stages of the immune response. When a pathogen enters the body, the immune system recognizes it as foreign and begins to produce antibodies, with IgM being the primary response antibody.

IgM has a pentameric structure, meaning it consists of five units. This configuration allows it to effectively bind to multiple antigens at once, providing a strong initial response to infections. Its presence indicates that the immune system has recognized and is actively responding to an antigen, making IgM a marker of early immune response.

Over time, as the immune response matures, other types of antibodies such as IgG become more prominent, but they are not the first responders. Understanding the role and timing of IgM is essential for grasping how the immune system protects the body from infections.