Which of the following substances make bacteria more susceptible to phagocytosis?

• A. Opsonins
• B. Allergens
• C. Haptens
• D. Interleukin 1

Answer: (A)

Opsonization is the process that makes bacteria more susceptible to phagocytosis. When bacteria are coated by opsonins, such as antibodies (especially IgG) and complement fragment C3b, phagocytes recognize these tags through Fc receptors and complement receptors, leading to efficient binding, engulfment, and killing of the bacteria. Allergens trigger allergic responses and are not involved in tagging bacteria for phagocytosis. Haptens are small molecules that become antigenic when bound to carriers and do not function as opsonins. Interleukin-1 is a cytokine that promotes inflammation and activates immune cells but does not directly coat bacteria to enhance phagocytosis. Therefore, opsonins best explain the increased susceptibility of bacteria to phagocytosis.