Final answer:
The μ heavy chains produced by late pro-B cells are essential components of the IgM antibodies and the B cell receptor, playing a key role in the immune response before B cell maturation to plasma cells.
Step-by-step explanation:
The question pertains to the function of μ heavy chains synthesized by late pro-B cells in the immune system. The μ heavy chains are part of the immunoglobulin M (IgM) class of antibodies, which are produced early in the adaptive immune response. B cells, including pro-B cells, undergo genetic rearrangement to create diverse antigen receptors, and late pro-B cells, in particular, are involved in synthesizing μ heavy chains for the formation of the B cell receptor (BCR) and the IgM antibodies. IgM molecules can be assembled into pentamers with the help of a joining (J) chain, enhancing their ability to bind to antigens, though not as stably as IgG antibodies that are secreted upon re-exposure to a pathogen. The μ heavy chains, as part of the BCR, play a crucial role in initiating the immune response before B cell maturation into plasma cells, which secrete large quantities of antibodies.