Final answer:
The IgH chain that is not produced as a result of Class Switch Recombination (CSR) is λ (lambda), a light chain not involved in the CSR process.
Step-by-step explanation:
The correct answer to the question "Which of the following IgH chains is NOT produced as a result of CSR?" is C. λ. CSR stands for class switch recombination, a process in which B cells alter the heavy chain of the antibody molecule to switch from producing one class of antibody to another. These classes include IgG, IgA, and IgE, which are initially secreted as pentameric IgM. The possible heavy chains involved in CSR are gamma (γ), alpha (α), and epsilon (ε), which correspond to the antibodies IgG, IgA, and IgE, respectively. However, lambda (λ) is a type of light chain, not a heavy chain, and is therefore not produced as a result of CSR. The lambda light chain can pair with any of the heavy chains, but it does not change during CSR.