Memory Cells in Immune Response Timeline

Steps:

• Vaccination causes primary antibody response: slow rise, peak, then decline, producing memory cells.
• Memory cells persist after primary response, enabling rapid secondary response upon infection.
• Graph likely shows low antibodies before infection (point 1), then sharp rise (secondary response).
• Thus, memory cells exist before point 1 (post-vaccination, pre-infection).

Why B is correct:

• Memory cells form during primary response to vaccination and remain in blood long-term, priming faster antibody production upon pathogen exposure (immunological memory principle).

Why the others are wrong:

• A: Memory cells are long-lived and persist beyond point 3 to drive ongoing immunity.
• C: Passive immunity requires external antibody transfer (e.g., maternal), not the active secondary response at 4.
• D: Memory cells appear after primary response (pre-point 2 if 2 marks early secondary), but were already present before 1.

Final answer: B