What do white blood cells form after encountering a pathogen for the first time?

• A. Red blood cells.
• B. Platelets.
• C. Memory cells.
• D. Antibody-producing plasma cells.

Answer: (C)

When the immune system first meets a pathogen, a branch of white blood cells called B cells is activated and can differentiate into two major outcomes. Some become plasma cells that rapidly produce antibodies to neutralize the pathogen right away. Others become memory cells that persist long term. These memory cells “remember” the specific pathogen so that if the same invader returns, the immune system can respond much faster and more effectively, often preventing illness.

That’s why memory cells are the best choice here: they are the lasting product that provides future protection after the initial encounter. Red blood cells and platelets aren’t involved in forming immune memory, and while plasma cells do produce antibodies during the first response, memory cells are specifically the long-lasting form that remains for future encounters.