In monoclonal antibody production, the specificity of the antibody is determined by the:

• A. Sensitized B lymphocytes
• B. Myeloma cell line
• C. Sensitized T lymphocytes
• D. Selective growth medium

Answer: (A)

In monoclonal antibody production, the antibody’s binding specificity comes from the B lymphocyte that originally recognizes the target antigen. These sensitized B cells carry the specific antibody genes that encode the antigen-binding site. When a single B cell is fused with an immortal myeloma cell, a hybridoma is formed that inherits that unique antibody specificity from the B cell. All descendants of that hybridoma secrete the same antibody, giving you a monoclonal product with uniform specificity.

The myeloma cell line’s role is to provide endless growth and immortality, not to determine what the antibody binds. T lymphocytes do not produce antibodies, so they don’t set the antibody’s specificity in this process. The selective growth medium (used to favor fusion hybrids) ensures survival of hybridomas, but it doesn’t define which antigen the antibody will recognize.