Paper I
Question
Differences between ‘T’ & ‘B’ lymphocytes
Answer
| Feature | T lymphocytes | B lymphocytes |
|---|---|---|
| Site of maturation | Thymus | Bone marrow |
| Type of immunity mediated | Cell-mediated immunity | Humoral (antibody-mediated) immunity |
| Surface receptor | T-cell receptor (TCR), associated with CD3 complex | Surface immunoglobulin (B-cell receptor, BCR) |
| Antigen recognition | Recognizes processed peptide antigen presented on MHC molecules (MHC-restricted) | Recognizes native/unprocessed antigen directly |
| Major subsets | CD4+ helper T cells, CD8+ cytotoxic T cells, regulatory T cells | — (differentiate into plasma cells and memory B cells on activation) |
| Effector function | Helper T cells secrete cytokines to coordinate immune response; cytotoxic T cells directly kill infected/abnormal cells | Differentiate into plasma cells that secrete antibody |
| Surface markers | CD3, CD4 or CD8, TCR | CD19, CD20, CD21, surface Ig |
| Approximate proportion of circulating lymphocytes | ~70–80% | ~10–20% |
| Memory | Memory T cells | Memory B cells |
| Antigen presentation | Do not typically present antigen to other T cells (except some subsets) | Can act as antigen-presenting cells for T-helper cells |
| Response to antigen | Proliferates and differentiates into effector/memory T cells | Proliferates and differentiates into antibody-secreting plasma cells and memory B cells |