Which antibody do developing B cells produce first?

Developing B cells initially express and produce IgM antibodies as their first type of immunoglobulin. This occurs during the early stages of B cell maturation in the bone marrow. The expression of IgM is crucial because it plays a significant role in the primary immune response. Upon activation by an antigen, B cells will undergo class switching, allowing them to produce other types of antibodies, such as IgG, IgA, or IgE, but the production of IgM is the first step in their functional response.

The presence of IgD is also noted on the surface of mature B cells, but it is not produced as the first antibody during the development process. IgA is primarily associated with mucosal immunity, and IgG is the most abundant antibody in circulation, often appearing after IgM during a secondary immune response. Understanding the order of antibody production in B cells is essential for grasping the adaptive immune response and the role each immunoglobulin plays in protecting the body against pathogens.