Final answer:
The first heavy chains produced during the pre-B cell stage are those for the IgM antibodies, which include a specific μ heavy chain associated with the B cell receptor on immature B cells.
Step-by-step explanation:
During the pre-B cell stage, the first heavy chains to be produced are those for the IgM class of antibodies. As a precursor B cell matures, it undergoes genetic rearrangements to create a diverse range of antigen receptors. This maturation process involves the production of an immunoglobulin heavy chain (mu μ heavy chain), which is part of the B cell receptor (BCR) and is associated with the IgM class. The μ heavy chain is composed of one variable domain (VH) that determines binding specificity and four constant domains (CH1, CH2, CH3, and Cμ4) that define the immunological function of the antibody. This IgM-heavy chain is crucial for the initial stages of B cell development and forms part of the BCR complex on the surface of immature B cells.