USMLE Step 1 · Immunology

T-cell maturation vs B-cell maturation

How to tell T-cell maturation and B-cell maturation apart when a board question makes them look alike.

Fastest separator

T cells mature in thymus and are MHC selected; B cells mature in bone marrow and later refine antibodies in germinal centers.

Side by side

T-cell maturationB-cell maturation

Key clue

T-cell maturation occurs in thymus with positive selection in cortex for MHC recognition and negative selection in medulla against self-reactivity.

B-cell maturation occurs in bone marrow with immunoglobulin gene rearrangement, central tolerance, and later germinal-center class switching and affinity maturation after activation.

Mechanism

Thymocytes rearrange TCR genes, become CD4/CD8 double positive, and are selected by thymic epithelial cells and medullary antigen presentation.

Developing B cells rearrange heavy and light chains, express surface IgM/IgD, and delete or edit strongly self-reactive receptors.

Labs and tests

Thymus, positive/negative selection, AIRE, CD4/CD8 lineage, and TCR restriction support T-cell maturation.

Bone marrow, surface immunoglobulin, receptor editing, plasma cells, and germinal centers support B-cell maturation.

The trap

Both rearrange antigen receptors and undergo tolerance, so organ site and MHC selection separate them.

The repair move

For lymphocyte development, attach T cells to thymic MHC selection and B cells to bone marrow immunoglobulin selection.

Try a free question

Core

Lymphocyte precursors from bone marrow migrate to the thymus, where they undergo TCR gene rearrangement, become CD4+CD8+ (double positive), and are subjected to positive selection in the cortex (cells that bind self-MHC moderately survive) and negative selection in the medulla (cells that bind self-antigen strongly are deleted). AIRE-expressing medullary thymic epithelial cells present tissue-restricted antigens. Which lymphocyte lineage matures this way?

Show answer and explanation

Answer: A. T cells. T cells mature in the thymus from bone marrow precursors. Stages: double negative (CD4-CD8-) -> double positive (CD4+CD8+) -> single positive (CD4+ or CD8+) after positive selection. Positive selection in the cortex (cells that bind self-MHC survive); negative selection in the medulla (cells that bind self-antigen strongly are deleted). AIRE (autoimmune regulator) drives medullary thymic epithelial cells to express tissue-restricted antigens; AIRE deficiency causes APECED (autoimmune polyendocrine syndrome type 1).

Why the other choices are tempting

B. B cells mature in the bone marrow, not the thymus.
C. NK cells mature in the bone marrow and lack TCR rearrangement.
D. Plasma cells are terminally differentiated B cells producing antibody.
E. Dendritic cells originate from myeloid or lymphoid precursors but are not subjected to thymic positive/negative selection with TCR rearrangement.

Flashcards

Tap a card to flip it.

What clue supports T-cell maturation?

Choose T-cell maturation when the stem gives this pattern: T-cell maturation occurs in thymus with positive selection in cortex for MHC recognition and negative selection in medulla against self-reactivity.

What clue supports B-cell maturation?

Choose B-cell maturation when the stem gives this contrasting pattern: B-cell maturation occurs in bone marrow with immunoglobulin gene rearrangement, central tolerance, and later germinal-center class switching and affinity maturation after activation.

Quick answers

What is the fastest way to tell T-cell maturation from B-cell maturation?