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Phase 2a - Introductory Clinical Sciences > Immunology > Flashcards

Flashcards in Immunology Deck (160)
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list the five classes of immunoglobulin



what is the function of IgG immunoglobulins?

important in secondary/memory responses.
main effector of humoral immunity. binds complement. can cross placenta.


what is the function of IgM?

low affinity and specificty. important in primary response - first line defence. fixes complement well.


what is the function of IgA?

protects mucosal surfaces.
is found in serum and secretions.


what is the function of IgE?

present a very low levels.
involved in allergy and response to parasitic infection.


describe how the specific binding properties of antibodies (Fab) help protect against infection

neutralize toxins
immobilise motile microbes
prevent binding to host cells.
form complexes - (each Ig can bind 2 pathogens).


how do antibodies enhance innate mechanisms to protect against infection (Fc)?

Activate complement
bind Fc receptors on:
phagocytes - enhanced phagocytosis.
mast cells - inflammatory mediator release.
NK cells - enhance killing of infected cells.


give some uses of antibodies in research, diagnostics and therapy

1. identify and label molecules in complex mixtures.
2. serotyping of pathogens.
3. identifying cell types.
4. "humanized" antibodies are used in therapy


where do T cells mature?

the thymus


what are the major T cell subtypes?

T helper cells (CD4+).
cytotoxic T cells (CD8+)
T regulatory cells (CD4+)


what are the roles of T helper cells?

help B cells make antibody.
activate macrophages and NK cells.
help development of cytotoxic T cells.


what is the role of cytotoxic T cells?

recognise and kill infected host cells


what is the role of T regulatory cells?

suppress immune responses


describe the structure of the T cell receptor

a heterodimer of either alpha/beta or gamma/delta chains.
similar to Fab arm of antibody.
each one is specific to an antigen.


how do T cell receptors recognise antigens?

as processed, cell-associated antigen.
recognise antigen peptides in context of MHC class I and II antigens.


which MHC classes do T helper and cytotoxic T cells recognise respectively?

T helper cells = MHC class II, use CD4 to enhance binding/signalling.
cytotoxic T cells = MHC class I, use CD8.


which cells are MHC I and MHC II expressed by?

MHC I = all nucleated cells.
MHC II = macrophages, dendritic cells, B cells


which T cells do MHC I and MHC II display antigens to, respectively?

MHC I displays them to CD8+ (cytotoxic) T cells.
MHC II = CD4+ (helper) T cells.


briefly describe the process of antigen presentation to cytotoxic T cells

1. virus infects cell
2. viral proteins are broken down in cytosol.
3. peptides transported to ER, bind MHC I
4. transported to cell surface
5. activated cytotoxic T cells kill infected cell by inducing apoptosis


briefly describe the process of antigen presentation to T helper cells

1. macrophage/dendritic cell/B cell internalises and breaks down foreign material
2. peptides bind to MHC II in endosomes
3. transported to cell surface
4. activated T helper cells help B cells make antibody, and produce cytokines that activate/regulate other leukocytes


what are cytokines?

small secreted proteins involved in communication between cells of the immune response.
produced/act locally.


how do cytokines act?

by binding to specific receptors on surface of target cells


list some of the main groups of cytokines, and their general action

interleukins - made by T cells
interferons - respond to viral infections
chemokines - chemotaxis, e.g. IL-8
colony stimulating factors (CSFs) - leukocyte production


what do TH1 cells do?

activate macrophages, cause inflammation.
promote production of cytotoxic T cells (cell-mediated immunity)
important in intracellular infections.
induce B cells to make IgG antibodies.


what do TH2 cells do?

activate eosinophils and mast cells.
important in helminth infections and allergy.
induce B cells to make IgE - promotes release of inflammatory mediators e.g. histamine from mast cells.


describe the properties and roles of T memory cells

survive after infection, in greater numbers than naive cells. respond to antigens rapidly.


what two things are needed for T cell activation?

antigen presentation in the form of a peptide presented on MHC.
a costimulatory signal.


what is the "epitope" of an antigen?

the portion of the antigen that is bound by antibody


list the types of bonds that may form between antibody and antigen?

charge interactions.
van der waals.
hydrogen bonds.


what are the main effector functions of antibodies?

complement activation.
ADCC (antibody dependent cell mediated cytotoxicity).
allergic responses and IgE.