Cross-protection via antibody cross-reactivity

Steps:

• The measles vaccine triggers adaptive immunity, producing memory cells for long-term protection.
• This immunity extends to other infections through non-specific or cross-reactive mechanisms.
• Evaluate options: focus on how memory cells contribute to broader defense without direct exposure.
• Select the choice describing antibody-mediated binding to unrelated pathogens.

Why B is correct:

• Memory cells differentiate into plasma cells that produce anti-measles antibodies capable of cross-reacting and binding to similar epitopes on other pathogens, providing heterologous immunity as per immunological cross-protection principles.

Why the others are wrong:

• A: Memory B-lymphocytes confer active, not passive, immunity; passive immunity is temporary and maternally derived or injected.
• C: Incomplete description lacks specificity on antibody binding to other infections, failing to explain cross-protection.
• D: Vaccines induce artificial active immunity, not natural (from prior infection); T-lymphocytes primarily handle cellular responses, not broad antibody-based protection.

Final answer: B