What is the functional consequence of immunoglobulin heavy chain class switch recombination?

• A. Alters the constant region to produce different effector isotypes while preserving antigen specificity
• B. Changes the variable region to alter antigen specificity
• C. Generates somatic hypermutation
• D. Increases antibody production

Answer: (A)

Heavy chain class switch recombination changes the constant region of the antibody while keeping the variable region—the part that binds antigen—the same. This means the B cell continues to recognize the same antigen, but the antibody it produces can have different effector functions because it now has a different isotype (for example, IgG, IgA, or IgE instead of IgM). The switch is achieved by recombination between switch regions upstream of different constant region genes, driven by enzymes like AID, and guided by T cell signals and cytokines. Therefore, the functional consequence is producing different effector isotypes with preserved antigen specificity.