PH3113 - Pain and Analgesia 8 Flashcards
What is the function of T cells?
Best suited for cell-to-cell interactions and target
- cells infected with
- viruses, bacteria or intracellular parasites
- abnormally or cancerous cells
- cells of infused or transplanted foreign tissue
How do T cells recognise infected tissue?
Recognise and respond to processed fragments of antigen displayed on the surface of antigen presenting cells (APC) via their T cell receptor (TCR)
How does a T cell receptor recognise an antigen?
Form of a complex
- peptide bound to an MHC molecule
What is the structure of the T cell receptor?
Heterodimer is composed of two transmembrane glycoprotein chains
- alpha
- beta
Extracellular portion of each chain consists of two domains
- immunoglobulin V
- immunoglobulin C
What does a T cell receptor recognize?
Processed antigen
- peptide fragment
- processed by antigen cells
What is the TCR repertoire?
Somatic recombination occurs physiologically in the assembly of the B cell receptor and T cell receptor genes
- V(D)J recombination
- amino acid sequences in the antigen-binding regions of T cell receptors that allow for the recognition of antigens from nearly all pathogens including
- bacteria
- viruses
- parasites
- altered self cells
- cancer
What is the T cell mediated immune response?
Cell-mediated immunity is needed for intracellular antigens
- T cells mediate cellular adaptive immunity
- CD4 cells (T4 cells) helper T cells
- TH1
- TH2
- TH17 cells
- recently discovered
- Treg cells
- homeostasis
- CD8 cells (T8 cells) cytotoxic T cells
- destroy cells harbouring foreign antigens
- memory T cells
What are the properties of CD4 T cells?
Carry co-receptor protein CD4
Recognise antigens derived from intravesicular sources
- TCR bind to MHC class II on APC
- differentiate into CD4 T helper cells
- TH1 and TH2 effector cells
- help/activate macrophages and B cell responses to antigen
- differ by the type of immune response they produce
- TH1 - intracellular parasites such as bacteria and viruses
- TH2 - helminths and other extracellular parasite
- imbalance linked to allergy/autoimmunity
What are the properties of CD8 T cells?
Carry co-receptor protein CD8
Can kill other cells
- cytotoxic T cells
- recognise antigens derived from cytosolic sources
- TCR bind to MHC class I on APC/infected body cell
Direct cell killing
- kills virus infected cells
- kills cancer cells
What are Treg cells?
Regulate or suppress other cells in the immune system to prevent excessive activation
- control the immune response to self and foreign particles
- antigens
- help prevent autoimmune disease
Natural Tregs express both
- CD4 T cell co-receptor
- CD25
- component of IL-2 receptor
TGF-beta is thought to induce differentiation of naive CD4+ into Tregs
Suppress activation, proliferation and cytokine production of CD4+ T cells and CD8+ T cells
Suppress B cells and dendritic cells
What are memory T cells?
Differentiate from both CD4+ and CD8+ T cells that have learned how to overcome an invader by ‘remembering’ the strategy used to defeat previous infections
Some of the activated T cells become memory cells
What are the two types of antigen-presenting cells?
Professional
Non-professional
How do cytotoxic T cells kill virus infected cells?
Release cytokines
Cytotoxic granules
- protein perforin
- punches holes in the target-cell membrane
- granzymes can enter
- able to induce apoptosis
How can cytotoxic CD8 T cells induce apoptosis in target cells?
Cytotoxic T cells can recycle to kill multiple targets
- serial killing
Each killing requires the same series of steps
- including T cell receptor binding to MHC and directed release of cytotoxic proteins stored in lytic granules
What is MHC class I?
Found on the cell surface of all nucleated cells
- endogenous
- intracellular
