Q.5 B-lymphocytes originate from the bone marrow whereas T-lymphocytes originate from
(A) thymus (B) bone marrow (C) spleen (D) liver

B-lymphocytes originate in bone marrow, while T-lymphocytes originate from bone marrow but mature in the thymus, making (A) the correct answer. This distinction defines adaptive immunity pathways in immunology.​

Correct Answer

The correct option is (A) thymus. T-cell precursors migrate from bone marrow to thymus for maturation, where they undergo selection for self-tolerance and TCR diversity. Mature T cells then populate lymph nodes and spleen.​

Option Explanations

Lymphocyte development separates B and T lineages post-bone marrow; T cells require thymic education.

• (A) Thymus: Correct; bone marrow progenitors seed thymus, developing into CD4/CD8 T cells via positive/negative selection.​

• (B) Bone marrow: Incorrect for T cells; primary site for B-cell maturation and common lymphoid progenitor origin for both.​

• (C) Spleen: Incorrect; secondary lymphoid organ for immune responses, not T-cell origin or primary maturation.​

• (D) Liver: Incorrect; fetal hematopoiesis site (hematopoietic stem cells), not postnatal T-lymphocyte origin.​

Mechanism Overview

Common lymphoid progenitors in bone marrow yield B cells (stay, express BCR) and T precursors (migrate to thymus via blood). Thymic epithelial cells support T-cell differentiation; immature T cells die by neglect or apoptosis if autoreactive.​