Question

The first antibodies to be produced in an immune response are always IgM. These early IgM antibodies are produced before B cells have undergone somatic hypermutation and therefore tend to be of low affinity. Why is IgM is usually confined to the blood?

Its charge
Its affinity
Its size
Its amount
Its specificity

Answer 1

IgM is usually confined to the blood due to its large size. As a pentamer, it is the largest antibody molecule and cannot easily leave the bloodstream to enter other tissues. This limitation allows IgM to focus on pathogens circulating in the blood during early immune responses. option C.

Step-by-step explanation:

The primary reason why IgM is usually confined to the blood is due to its size. IgM is composed of five monomers, making it a pentamer, which is the largest antibody molecule in the immune system. Due to its large size, it is challenging for IgM to move out of the bloodstream and enter other tissues.

IgM antibodies are the first to be produced in response to an infection.

These antibodies are significant in the initial stages of the immune response before more high-affinity antibodies, like IgG, are produced following somatic hypermutation. IgM has ten antigen-binding sites, which allows it to bind pathogens effectively despite its lower affinity compared to other antibodies that appear later in the response.

The large pentameric structure of IgM, linked by a joining (J) chain, primarily restricts it to the bloodstream where it can provide a rapid defense against pathogens circulating in the blood. Option C.