Lymphocytes Flashcards
What do CD4 T cells do?
Produce cytokines to help shape immune response.
What do CD8 T cells do?
Kill infected cells.
What do B cells do?
Produce antibodies.
What is meant by the humoral response?
Response driven by b cells. Also known as antibody mediated response.
What is meant by cell mediated response?
Response driven by t cells. Cells do the work.
What is the Epitope?
The region of an antigen which the receptor binds to.
How do B cell recognise antigens?
Recognise structural 3D epitopes - native antigens.
How do T cells recognise antigens?
Recognise linear epitopes that are peptides derived from proteins processed by APC’s
What happens when lymphocyte receptor binds to antigen?
Leads to activation of cell and clonal expansion which results in differentiated effector cells of that lineage that bear the same receptor.
What generates the diverse b cell repertoire?
Immunoglobulin gene rearrangement. DNA is rearranged before transcription.
Explain production of BCR receptor chain?
Each BCR receptor chain is encoded by separate multigene families on different chromosomes. During B cell maturation these gene segments are rearranged and brought together. Transcription of B cell DNA then occurs. RNA is then spliced and mRNA is translated to produce polypeptide for that chain that will make up part of the B cell receptor.
What presents antigen to T cell?
MHC (Major histocompatibility complex).
What is the point of MHC?
Defines self and not self. Presents antigens to T cells.
Where is MHC I found?
All nucleated cells.
Where is MHC II found?
All antigen presenting cells.
How are viral proteins recognised as foreign?
Displayed on MHC I.
How many chains does MHC I have?
One alpha chain.
How many chains does MHC II have?
Two. One alpha, one beta chain.
What type of antigen does MHC I present?
Intracellular antigen.
What type of antigen does MHC II present?
Extracellular antigen.
What does MHC I present to?
CD8 T cells.
What does MHC II present to?
CD4 T cells.
Examples of APC cells?
Macrophage, dendritic cell and b cell (despite role in humoral immunity).
Characteristics of MHC gene expression?
Polygenic (up to 6 genes) and co dominant expression.
Where are MHC I peptides processed?
Cytosol.
Where are MHC II peptides processed?
Endosomes.
What class of T helper cell would be involved in a viral and intracellular bacteria infections?
Th1.
What immune cells would be seen in a viral/intracellular bacterial infection?
CD8 T cells, NK cells, Th1 cells, neutrophils and macrophages.
What immune cells would be seen in a parasitic infection such as a helminth?
Eosinophils, basophils, Th2 cells, B cells and macrophages.
What immune cells would be seen in an extracellular bacterial infection or fungal infection?
Th17, neutrophils and macrophage.
What are the different types of t helper cells?
Treg (Th0), Th1,Th2, Th17, T follicular helper cell (Tfh).
T reg role and cytokines?
IL-10 and TGF beta.
Th1 role and cytokines?
Boosts cellular immune response. IF gamma, TNF and IL-12.
Th2 role and cytokines?
Pro allergic. IL-4, IL-5 and IL-13.
Th17 role and cytokines?
Pro Inflammatory (controls bacterial and viral infection). IL-17, IL-23 and IL-6.
Tfh role and cytokines?
Pro antibody. Produces the cytokine IL-21 which drives B cell proliferation.
Where are t follicular helper cells found?
Secondary lymphoid organs in b cell zones.
How does CD8 T cells kill infected cells?
Apoptosis. Released perforin which polymerise and form pores in the pathogen cell membrane, then released granzymes through pore that create a cascade that leads to apoptosis by fragmentation of nuclear DNA.
How do CD8 T cells distinguish infected and non infected cells?
In uninfected cells, MHCI molecules show self peptides. CD8 cell looks for non self peptides presented on MHCI. A virus infects the cell. The cell now starts making viral proteins and viral peptides are displayed on MHC. The CD8 cells detects the non-self peptides on MHC. The CD8 cell kills the virally infected cell.
What are the 3 functions of antibodies?
Neutralisation, Opsonization and complement activation.
How can an antibody neutralise a pathogen?
It can block outer proteins that allow it to enter the cell. Prevents pathogen from working.
What is opsonization?
Antibodies promoting phagocytosis. Macrophages can bind to constant region of antibodies via their fc receptors and phagocytose pathogen.
What is complement activation?
Activation of complement system which enhances opsonisation and lyses some bacteria.
Key facts about IgG?
Most common antibody. Highest opsonization and neutralization activies.
Key facts about IgM?
Largest antibody. Produced first in response to antigen invasion.
Key facts about IgA?
Expressed in mucosal tissues. Forms dimers after secretion.
What antibody is mainly in the respiratory and digestive tracts?
IgA.
Key facts about IgE?
Involved in allergy.
What results in different classes of antibodies.
Different constant region. Different classes bind to different receptors.
What class of antibody do thymus independent antigens stimulate production of?
Induce IgM synthesis by B cells.
What class of antibody do thymus dependent antigens stimulate production of?
All Ig-classes.
What do thymus independent antigens not stimulate?
They do not stimulate immunological memory.
What are thymus independent antigens?
Activate B cell without help of T cells. Needs to have repetitive structure (e.g bacterial surface sugars).
How do thymus independent antigens activate B cell?
B cell receptor binds to repetitive structure present on bacterial surface. Second signal provided by PAMP such as LPS which binds to toll like receptor on b cell.
Explain thymus dependent antigen pathway?
B cell ingest pathogen and antigen is internalised and degraded into peptides. Displays antigen peptides on its b cell receptor. DC ingests pathogen and displays peptides on MHC II. CD4 T cell that has complementary TCR to antigen gets activated by DC cell. T helper cell then activated B cell by costimulation and cytokines. B cell turns into plasma cell and produces antibodies for that antigen.
