B and T lymphocytes Flashcards
What is the difference between positive and negative selection of T cells in the thymus?
The T cells are first taught to recognise antigens, and any that don’t are killed - this is positive selection. Then the T cells that have learnt to recognise self cells (autoreactive) are killed - this is negative selection.
What form of antigen do T cell receptors recognise?
Linear epitopes, presented by Major Histocompatibility Complex.
How many polypeptide chains is the T cell receptor made up of?
2, alpha and beta.
What is the major gateway to B cell activation?
CD4+ helper T cells forming a synapse and secreting cytokines at the B cell.
What form of antigen do B cell receptors recognise?
Conformational epitopes.
What is the name of the specialised transport system which transfers antigen fragments from the phagolysosome to the cell surface to be presented?
Major Histocompatibility Complex II.
Called Human Leukocyte Antigen (HLA) in humans.
What is the function of MHC I?
Presents peptide fragments produced in all cells to CD8+ cytotoxic T cells, so cells like tumour cells or virus infected cells that produce abnormal proteins can be detected and destroyed.
What is the function of MHC II?
Presents peptide fragments from the phagolysosome of antigen-presenting cells to CD4+ helper T cells.
What is it called when T cells have to recognise the antigen presented by MHC but also have to recognise another signal (e.g from TLR of innate immune system) before they can be activated? What is the point of this?
Costimulation. To prevent autoimmunity.
Why does inflammation facilitate the presentation of antigens to T cells?
More fluid moves into the tissue, which increases the pressure so fluid drains into the lymphatic system at an increased rate, so antigen presenting cells will reach the lymph nodes faster.
Which phagocytic cells are specialised to move from the site of infection to lymph nodes to carry information to adaptive immune cells?
Dendritic cells.
Where are the inactivated T cells in the lymph node?
Paracortex.
What’s the difference between primary and secondary lymphatic follicles in the lymph node cortex?
Primary follicles contain B cells that aren’t yet activated. Secondary follicles occur when an immune response is being mounted, and there is a germinal centre (with B cells proliferating and carrying out somatic hypermutation) giving rise to plasma cells and memory B cells.
What’s the difference between the way antibodies and T cells and plasma cells leave the lymph node?
Antibodies can leave in the blood vessels, B and T cells leave in the afferent lymphatic vessels and rejoin the blood via the thoracic duct.
What is the name of dendritic cells in the skin?
Langerhan’s cells.
