MRCS PART A · APPLIED BASIC SCIENCES
Immunology: antigen recognition and linked presentation
Two selected surgical-immunology foundations: peptide–MHC recognition and the different specificities of B and T cells in linked presentation. Two foundation SBAs and two separately scored transfers use fictional controlled assays. Sources checked. This is not a complete immunology course, a vaccine recommendation or an exam-readiness measure.
2 topics · 4 original SBAs
1 · Change the peptide or the presenting molecule
Your task: Interpret conventional alpha-beta T-cell recognition as a peptide–MHC combination, not free antigen alone.
What does a conventional alpha-beta T-cell receptor encounter?
A peptide displayed by an MHC molecule. Both parts can affect recognition; finding the same peptide in a sample does not establish the same surface ligand.
Does this rule cover every lymphocyte receptor?
No. The scope here is conventional peptide–MHC-restricted alpha-beta T cells, not every unconventional T-cell system.
Does a different MHC molecule necessarily preserve a clone's response?
No. Test that clone against the new combination. Do not infer universal recognition from one responsive combination.
What should the comparison keep constant?
Cell viability, measured surface-complex abundance and the assay's other activation conditions. Otherwise a missing signal could reflect a different uncontrolled step.
Is detecting a ligand the same as demonstrating a whole immune response?
No. A receptor-binding or reporter result answers the specified experimental question, not every later immune outcome.
Can an accessory receptor replace the TCR's specificity?
No. CD8 can stabilise a TCR–class I interaction, but does not make every peptide–MHC combination equivalent. Additional primary reference: https://pubmed.ncbi.nlm.nih.gov/8955273/
2 · Follow what the B cell captures and the T cell sees
Your task: Distinguish B-cell antigen binding from carrier-peptide recognition by a responding T cell.
What is a hapten–carrier model?
A small determinant H is attached to a protein X. In this model the selected B cell binds H, while the responding T cell recognises a peptide from X presented by the B cell.
Must the two cells recognise the same epitope?
No. Their recognised determinants differ, despite being carried in the same captured material.
Why trace the captured material rather than just the fluid around the cells?
B-cell binding, uptake and presentation are distinct steps. A carrier somewhere in the fluid is not evidence that the selected B cell displays its peptide.
Does mixing unlinked components always reproduce linked presentation?
Do not assume it. Dose, uptake and other antigen-presenting cells matter. This lesson's questions specify what was actually captured and displayed.
If carrier X is replaced by Y, what might remain unchanged?
Binding to H can remain intact while the carrier peptides change. Measure binding and presentation separately.
What can an antigen-specific T-cell reporter establish?
Its measured response under the stated conditions. It does not alone establish antibody concentration, class switching, protection or clinical vaccine efficacy. Additional primary reference: https://pubmed.ncbi.nlm.nih.gov/3155791/