Past Papers · SAQ
Immunity — B/T Lymphocytes
2012A Q07
Exam questionCompare and contrast the characteristics of B and T lymphocytes.
CICMWrecks answer
Master answer
Lymphocytes are responsible for acquired immunity
Antigens on foreign material stimulate proliferation and immune response
- In T and B cells, there a millions of different clones which express different antigen binding site
- Each lymphocyte clone is highly specific for a particular antigen, and can only be activated by it
| T cell | B cell | |
|---|---|---|
| Cell mediated Immunity | Humoral Immunity | |
| Origin | Haemopoeitic stem cells in bone marrow → common lymphoid progenitor cell | Haemopoeitic stem cells in bone marrow → common lymphoid progenitor cell |
| Site of differentiation | Thymus | Liver in mid-foetal Bone marrow in late-foetal and after birth |
| Site of storage | Lymph (thymus, spleen, submucosa of GIT, bone marrow, lymph glands) | Lymph (thymus, spleen, submucosa of GIT, bone marrow, lymph glands) |
| Receptor | T cell receptor Only respond to antigens bound to antigen-presenting cell (macrophage) | B Cell receptor (Immunoglobulin molecules) Can bind to antigens directly |
| Mechanism of activation | Antigen binds to major histocompatability complex on 1) macrophages 2) B-lymphocytes 3) dendritic cells Antigen bound to MHC is sensed by surface receptor | Activated following T-cell activation |
| Type of immunity | Cell-mediated Cytotoxic T cells bind to pathogen (via antigen) → Release perforins → Punch holes in cell membrane → Also release cytotoxics into these holes | Humoral Antibody can cause: Precipitation Lysis Agglutination Neutralisation Antibody-antigen complex activates complement cascade → pathogen damage → recruitment of phagocytes and local inflammation |
| Derived cells | Helper T cells Encourage proliferation of cytotoxic and suppressor T cells Stimulate B-cell proliferation Attract and activate macrophages Cytotoxic T cells Suppressor T cells Suppress both cytotoxic and helper T cells Memory T cells Circulate until reactivation | Plasma cells Produce IgG antibodies and release them into lymph → blood Memory B cells Propogate and circulate to all lymph tissue, ready for reactivation |
| Function | produce antibodies that can bind to and neutralize extracellular pathogens or toxins | recognize and eliminate intracellular pathogens, such as viruses, or help other immune cells to do so |
| Lifespan of memory cells | Many years | 6-12 months (as B memory cells can reactivate them) |
Mooney 2016
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2012A Q07 | Compare and contrast the characteristics of B and T lymphocytes. | 40% |