Primary sites of lymphocyte activation by antigen Where are naive lymphocytes typically activated after encountering antigen from peripheral tissues?

Introduction:
Adaptive immune responses are initiated in specialized secondary lymphoid tissues. Recognizing the correct anatomical site helps interpret clinical signs such as regional lymph node enlargement during infections or after vaccination.

Given Data / Assumptions:

• Antigen originates from peripheral tissues (e.g., skin, muscle).
• Dendritic cells transport processed antigen via lymphatics.
• Naive T and B cells continuously traffic through lymph nodes.

Concept / Approach:

Lymph nodes are designed for antigen presentation: afferent lymph brings antigen/APCs; distinct microanatomical zones (T cell area, B cell follicles) facilitate activation and help.

Step-by-Step Solution:

Verification / Alternative check:

Vaccine responses correlate with activation in regional lymph nodes, evidenced by germinal center formation and node swelling.

Why Other Options Are Wrong:

Option A: Blood transports cells and antigen but is not the main activation site.

Option B: Bone marrow is a primary organ for hematopoiesis and some B cell development, not peripheral activation.

Option C: Liver filters blood and performs metabolic functions; not a canonical activation center.

Option E: Skin contains innate sentinels, but naive lymphocyte activation requires lymphoid organs.

Common Pitfalls:

Confusing lymphoid development sites (bone marrow, thymus) with activation sites (lymph nodes, spleen, MALT).

Final Answer:

Lymph nodes