Lymphocytes Flashcards
What are the characteristics of lymphocytes?
Inability to clear infection without them
Protects from secondary infection due to memory
Focuses response to site and organ
Needs time to develop
Can result in auto-immunity
What lymphocyte results in Cell-mediated response
What lymphocyte results in humoral response?
T cells - produce cytokines - CD4 helps and CD8 kills
B cells - produce antibodies
How do t and B cells recognise pathogens?
TCR
BCR
What is the Epitope?
The region of an antigen which the receptor binds to :
- antibodies recognise structural epitopes
- T cells recognise linear epitopes ( in the context of MHCs)
- The paratope is the area of the antibody which binds
What is clonal expansion?
Unique receptor and foreign antigen interaction allows activation and expansion of the receptor cell
Differentiated effector cells of that lineage will have the same receptor
How is antigen receptor diversity generated?
Recombination - Immunoglobulin gene rearrangement
Each BCR receptor chain ( Kappa, Lambda, heavy chain genes ) is encoded by separate multigene families on different chromosome
Describe the structure of the T cell receptor?
Alpha and Beta region make up variable region
Cytoplasmic tails connected by disulphide bonds and go through transmembrane
What are the differences between MHCI and MHCII?
MHC class I : found on all nucleated cells at various levels MHC class II : found in 'professional' antigen presenting cells
MHC class I : has single variable alpha chain and common beta microglobulin added MHC class II : has 2 chains, alpha and beta
How do genes control the MHC?
Encoded by HLA genes
Polygenic so 3 class I and II loci
Co-dominant expression
- so if a person was completely heterozygous they could have up to 6 of each gene
What MHC - TCR interactions occur in the cytosol?
For intracellular antigens
The antigen is presented on the MHCI taken from the target cell it is attached to
Presented to CD8 T cells
What MHC - TCR interaction occurs in endosomes?
CD4 binds to the beta2 domain of the MHC class II
For extracellular antigens
The antigen is presented on the MHCII
Presented to CD4 T cells
What roles do CD4 T helper 1 cells play?
- Pro - inflammatory
- Boost cell immune response - viruses
- Tumour necrosis factor
- Interleukin 12
What roles do CD4 T helper 2 cells play?
- Pro allergic
- Multicellular response - parasitic
- IL-4, IL-5, IL-13
What roles do CD4 TH0 regulatory cells play?
- Anti inflammatory
- Limit immune response
- IL-10, TGFbeta
What roles do CD4 T helper 17 play?
- Pro inflammatory
- Bacterial / fungal infection - in skin wounds not in the cells
- IL-17, IL-23, IL-6
What roles do CD4 T follicular helper cells play?
- Pro antibody
- IL-21
work with B cells to make better antibodies
What do CD8 cytotoxic T lymphocytes do?
Kill through apoptosis when they notice non-self MHC
CTLs store perforin, granzymes, granulysin in granules
How do antibodies work against bacteria?
Neutralisation - prevents bacterial adherence
Opsonisation - Promotes phagocytosis
Complement activation : enhances opsonisation and lyses some bacteria
When is the BCR formed, before or after cell encounters antigen?
Before cell encounters antigens
* can bind to soluble antigen, doesn’t need a MHC
What requires an accessory signal?
Naive B cells require accessory signals
Directly from microbial constituents
or
From t helper cells
How is antibody production by B cells achieved?
what two methods
T helper
Thymus dependent
All Ig classes, has memory
or
Microbial constituents
Thymus independent
only IgM, no memory
What antigens can activate B cells independently of the thymus?
Polysaccharide repetitive antigen structures
A second signal con be provided by microbial PAMP
Describe thymus dependent antibody production?
Membrane bound BCR recognises antigen, B cell with internalise the antigen and present its peptides on a MHCII itself.
Separately, Dendritic cells also notice the antigen and present it to CD4 helper cells which become activated
Activated CD4 then notices the antigen on the MHCII on B cell, activates help pathway:
- cytokines and cell markers = activate B cells
= antibody production
