Memory cells accelerate secondary immune responses

Steps:

• Primary immune response activates naive lymphocytes, which take time to proliferate and differentiate.
• During primary response, some activated lymphocytes become long-lived memory cells.
• Secondary exposure to the same antigen directly activates memory cells, bypassing naive cell activation.
• Memory cell activation leads to rapid proliferation and effector production, speeding up the response.

Why B is correct:

• Memory T-lymphocytes persist after primary infection and rapidly expand upon re-exposure, per adaptive immunity principles, enabling quicker pathogen clearance.

Why the others are wrong:

• A: Helper T-lymphocytes coordinate responses but do not persist as memory cells for faster secondary activation.
• C: Phagocytes engulf pathogens innately, without specific memory for accelerated responses.
• D: Plasma cells produce antibodies short-term in primary responses, not enabling long-term rapid secondary reactions.

Final answer: B