Cell-Mediated Immunity Flashcards
Describe antigen-binding chain formation
- Each T cell has about 30,000 identical TCR on its surface
- Each TCR is formed from multiple glycol-protein chains
- 2 chains are paired to form the antigen-binding site + others transmit signal generated by antigen-binding to cell
Name + describe the regions of an antigen-binding chain
- Variable region (aa sequence varies among T cells)
- Constant region (aa sequences stays the same)
- Transmembrane domain (very small paired chains linked by disulphide bond to form stable heterodimer)
How is T cell diversity generated?
Somatic DNA Recombination
Describe signal transduction in the immune system
When antigen binds to TCR a signal is generated that triggers a T response- paired antigen-binding chains of each TCR are associated w/ cluster of proteins (CD3 complex)
Classify the different types of MHC molecules + how they relate to cell cooperation in immunity
MHC class I = 3 alpha helices expressed on all nucleated cells of the body except RBCs, platelets + nerve cells MHC class II = 2 alpha helices, 2 beta helices- only expressed on surface of professional APCs
What complexes determine the class of MHC molecule that can be recognised by T cells?
CD4- found on T helper cells, binds MHC class II CD8- found on cytotoxic T cells, binds MHC class I
What other processes, in addition to formation of antigen- MHC complex, need to occur to trigger helper T cell response?
- adhesion molecules must bind T cells + APCs together
- T cells must be stimulated by cytokines secreted by APCs
What role do cytokines have in signal transduction?
determine the way in which T cells respond to antigens
Explain how recognition of ‘self’ occurs
- all nucleated cells produce proteins that are continuously degrade by cell to peptide
- ‘self’ peptides are expressed on cell-surface within groove of the MHC molecule
- circulating T cells don’ respond when peptides are normal products of the cell (self)
Explain how recognition of foreign antigens occurs
- If cell is abnormal, peptides expressed are altered + recognised by T cells
- Peptide MUST be presented in MHC molecule for it to be recognised by T cells = MHC/. genetic restriction of immune response
Describe the MHC class I pathway as a route of antigen entry
- proteins processed via cytosol + proteasome
- peptides presented by MHC class I molecules on APCs
- recognised by TCR of CD8 cytotoxic lymphocytes
Describe the MHC class II pathway as a route of antigen entry
- proteins processed by endocytic pathway
- peptides presented by MHC class II molecules on surface of APCs
- recognised by TCR of CD4 T helper lymphcytes
- cytokines secreted- enhances humoral + cellular immune response
Describe the different routes of antigen entry
- phagocytosis/ endocytosis/ binding to sIg- exogenous antigen processing, MHC class II restricted
- direct entry to cytosol- endogenous antigen processing, MHC class I restricted
What is the function of Th1?
Promotes cell-mediated immune responses
What drives the production of Th1?
IL-12 from antigen-presenting dendritic cells, macrophages + B cells
What is the function of Th2?
stimulates Ab production + switching
What are the major stimulators of Th2?
IL-4, IL-33, TSLP
What does IL-4 do with regard to Th2?
simulates B cell growth + differentiation, activates mast cells
Describe the postulates of clonal expansion
- each lymphocyte bears a single type of receptor w/ unique specificity
- interaction b/w foreign molecule + TCR capable of binding that molecule w/ high affinity leads to lymphocyte activation
- differentiated effector cells derived from an activated lymphocyte will bear receptors of identical specificity to those of the parental cell
- lymphocytes bearing receptors specific for ubiquitios self molecules are deleted at an early stage in lymphoid cell development + so absnet from repertoire of mature lymphocytes
