Final Answer:
IgM is a marker for _B lymphocytes_.
Step-by-step explanation:
Immunoglobulin M (IgM) is a class of antibodies and is considered a marker for B lymphocytes, which are a type of white blood cell involved in the immune response. Each B lymphocyte expresses a specific B cell receptor on its surface, which is a membrane-bound antibody.
In the case of B cells, the predominant antibody class expressed initially is IgM. IgM is the first antibody class produced during an immune response, and it plays a crucial role in the early stages of defense against infections.
B lymphocytes undergo a process called class switching, where they can change the class of antibody they produce, including IgM, IgG, IgA, IgE, etc. However, IgM is particularly associated with the initial response to antigens. B cells expressing IgM antibodies are involved in the recognition and neutralization of pathogens, triggering the activation of other immune cells and the overall immune response. As the immune response progresses, B cells may undergo class switching to produce other antibody classes with different effector functions.
Understanding the association between immunoglobulin classes and specific cell types is fundamental in immunology. IgM's role as a marker for B lymphocytes highlights its significance in the early stages of immune defense, serving as a key player in the body's ability to recognize and combat pathogens.