Sites of lymphocyte maturation in humans — primary lymphoid organs In human immunology, B cells and T cells mature in which primary lymphoid organs, respectively?

Introduction / Context:
Lymphocyte development occurs in specialized primary lymphoid organs before antigen-driven activation in secondary lymphoid tissues. Correctly identifying maturation sites is foundational for understanding immune ontogeny, immunodeficiencies, and vaccination responses.

Given Data / Assumptions:

• Question pertains to humans (not birds or other species).
• Focus is maturation (development), not activation.
• Primary lymphoid organs differ between species.

Concept / Approach:
In humans, B lymphocytes mature in the bone marrow. T lymphocytes mature in the thymus, where positive and negative selection yield a repertoire that is self-MHC restricted and self-tolerant. Secondary organs (lymph nodes, spleen, MALT) are where mature lymphocytes encounter antigen and undergo activation and clonal expansion.

Step-by-Step Solution:

Verification / Alternative check:
Clinical immunology texts describe severe combined immunodeficiency and DiGeorge syndrome as disorders of marrow-derived lymphopoiesis and thymic development, respectively—underscoring organ-specific roles.

Why Other Options Are Wrong:

• Lymph nodes/spleen: secondary sites; not primary maturation organs.
• Bursa and thymus: correct for birds, not humans.
• None/spleen–bone marrow: mismatched or incorrect pairings for human maturation.

Common Pitfalls:
Transferring avian anatomy (bursa) to humans; conflating maturation with activation sites.

Final Answer:
Bone marrow and thymus