Which describes a component of humoral immunity?

• A. T and B cells in lymph nodes
• B. Neutralization of toxins by serum
• C. Cells involved in phagocytosis
• D. Macrophages and mast cells in the tissue

Answer: (B)

Humoral immunity is the antibody-mediated arm of the adaptive immune response, with antibodies circulating in serum to target extracellular pathogens and toxins. Neutralization of toxins by serum captures this idea perfectly: antibodies bind toxin molecules in the blood, blocking their ability to interact with host cells and cause harm. This serum-based, antibody-driven action is the essence of humoral immunity. In contrast, the other descriptions refer to cellular components or innate immune cells (phagocytes, tissue macrophages, mast cells) that operate outside of the antibody-mediated serum response, so they don’t represent the humoral aspect.