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What is an allergic reaction?

An overactivation of the adaptive immune system in response to a typically normal thing.


What is an antigen based upon the old and new definitions?

An antigen is an antibody generator.
Used to be defined as causing an immune response.
Now is defined as interacting with antigens, not necessarily causing an immune response.


What is an immunogen?

An antigen that can cause an immune response.


What are epitopes?

Antigenic determinants.
Discreet regions of the antigen molecule that is specifically recognized by the adaptive immune system.
Ex: 10 or more amino acid sequence or 3D protrusion of molecule.


What is an antibody?

The main immune cell produced by B-lymphocytes (B cells) that neutralizes free-floating particles


What happens to B cells in response to antigens?

They proliferate and differentiate into plasma cells (antibodies and memory cells)


What is the structure of an antibody?

The 2 arms bind to the specific antigen (variable region)
The stem is recognized by the immune system (phagocytes) for destruction (constant region).


How do the light chains affect the antibody?

Can be gamma or K based upon the amino acid sequence in the constant regions.
2 light chains.


How do the heavy chains affect the antibody?

Higher molecular weight.
2 heavy chains
5 types based upon the amino acid sequence of the constant region. This gives the class of the antibody type (IgM, IgG, etc)


What is IgG?

The most common immunoglobulin.
Has basic monomeric structure.
There are 4 subclasses based on the amino acid sequence of the C regions of H chains (IgG1, IgG2, etc.)
IgG1 is the most prevalent.


What are the functions of IgG?

Opsonization: The coating of the antigen so that it is seen as a flag for phagocytes when Fab is bound to the antigen and Fc is freely exposed.
Neutralizes viruses and toxins
Main antibody in secondary response (when body encounters it again after the first time)
Crosses the placenta, providing passive immunity for the placenta
Has negative feedback on the immune system to suppress


What is IgM?

Can exist as a monomer, when attached to the B cell surface as a receptor or as a pentamer when in serum (held together by a J chain)


What are the functions of IgM?

The first antibody produced during the primary response
The antigen receptor on B cells.
Activates part of innate defences, stimulates activation of T cells
Agglutinates particulate antigens (bacteria)


What is IgD?

A monomer found in serum and on the B cell surface as a receptor
Found in very low amounts
Has an unknown function


What is IgA?

The primary antibody secreted by cells of the mucous membranes
Low amount and monomeric in serum but dimeric in secretions


What are the functions of IgA?

Neutralizes bacteria and viruses by preventing them from attaching to mucous membranes
Passes passive immunity through breast milk


What is IgE?

A monomeric antibody found in low levels in serum
Antigen receptors on mast cells (tissues) and basophils (blood)


What are the functions of IgE?

Anaphylactic hypersensitivity


What does it mean when you find only IgM in the blood?

There is a very recent infection present (acute).
No IgG


What does it mean when you find only IgG in the blood?

There is an infection that has been around for a very long time (chronic).
No IgM,


How does the humoral immune response work?

The classical complement pathway is activated first.
When an antibody binds to an antigen C1 is activated and splits C4 and C2 to form C4b2a (C3 convertase) which splits C3 into C3b and C3a
C3b binds to the microbe-antibody complex and the remaining components join in to form the MAC attack.
C3a works with C5a to act as anaphylatoxins.


What does the humoral immune system do?

Activate phagocytic cells by binding phagocytes
Neutralization by blocking the receptors of viruses, toxins and nutrient transport molecules.


What are T-lymphocytes (T cells)?

Cells that mature in the thymus
Recognize an antigen presented by one of the body's own cells (not free), that is complexed with an MHC
Help macrophages kill intracellular parasites
Inhibit intracellular replication of viruses
There are Cytotoxic T cells and Helper T cells.


How do T-cells work?

The T-Cell receptor binds to the complex of MHC molecules and peptide and then activates.
Act as surface markers


What happens when there is both Th1 cells and Class 2 MHC?

The T-cell releases macrophage activating factors


What are cytotoxic T cells?

Has a CD8 protein on it
Differentiate into Tc which destroy infected or cancerous cells.
Recognize antigens presented by MHC Class I


What are helper T cells?

Has CD4 protein on it
Differentiate into Th1 which activates macrophages and Th2 which activates B cells and produces interleukins
Recognizes antigen presented by MHC Class II


What happens when parasites are larger than the phagocytic cells?

Antibody-dependent cellular toxicity (ADCC)
The effector cells bind to antibody molecules, coating the target cells and activate.
Macrophages, eosinophils and NK cells are released to damage the targets.


What is the lymphoid system?

A collection of tissues and organs designed to bring B and T cells into contact with antigens that enter the body.
Since lymphocytes only recognize 1 or 2 antigens, they need to be brought around to find it.


What are lymphatic vessels?

Vessels that carry lymph collected from fluid that bathes the body tissues.
Lymph goes from the capillaries into surrounding tissues, supplying them with oxygen and nutrients from blood.
Most lymph will reenter capillaries but some with reenter lymphatic vessels and are taken back to lymph nodes where cells and proteins are removed.


What are the primary lymphoid organs?

Bone marrow and thymus
Both B and T cells originate in bone marrow
B cells mature in bone marrow
T cells mature in the thymus


What do T and B cells develop from?

Hematopoietic stem cells in the bone marrow


What happens when lymphocytes mature?

They gather in the secondary lymphoid organs, waiting to encounter antigens


What are secondary lymphoid organs?

Sites where lymphocytes gather to collect antigens (lymph nodes, spleen, tonsils, appendix)
When lymphocytes make contact with the antigen they proliferate, forming clones of cells specific for that antigen


What are mucosal associated lymphoid tissue (MALT)?

IgA play a key role in the adaptive immune response that prevents microbes from invading the mucosal surface.
Proteases, lysozme in the saliva
If it does enter, IgE works


What are skin associated lymphoid tissue (SALT)?

Prevents microbes from invading the skin.


What is clonal selection of B cells?

Only B cells are capable of making sure the correct antibodies bind to the antigen.


What is clonal expansion of B cells?

When cells bind to the antigen, they begin dividing and produce a population of clones.
Can have small mutations to evolve and a few may become memory cells (CD27, IgG, IgA or IgE)


What else is required by lymphocytes before activation can occur?

A 2nd opinion (accessory signal) from helper T cells (Th) before it can proliferate fully and causes cytokine release


How is the 2nd opinion before full proliferation helpful?

Helps prevent the immune system from mounting a response against itself.


How is the clonal selection and expansion of T cells compare to that of B cells?

The process itself is similar.
Some the cells release cytokines, others have cytotoxic functions.
There is no further selection as a result of somatic mutations.
Some of the expanded will differentiate into T memory cells and CD45RO.


Is the epitope that interacts with T cells the same as the one that interacts with B cells?



What are memory cells?

Cells that are more readily stimulated by an antigen, will mount an even greater response with B cells (mutation and selection) and T cells (increased expression of accessory adhesion molecules)
Basic principle of vaccines


How does T lymphocyte activation (T-dependent antigens) work?

Phagocytes eat a pathogen and present the antigen. T cells recognize the MHC-antigen complex that is presented and then begin to differentiate.


What is the difference between Class I and Class II MHC?

Class II is expressed by macrophages.
Class I is expressed by all body cells.


What are T independent antigens?

Instances in which the T cell is not need to activate the B cell.
Polyclonal activators, repeating determinants.


What are polyclonal activators?

Stimulate a wide variety of B cells independently of their specific antigen receptors


What are repeating determinants?

Give rise to low affinity IgM rather than IgG antibody response and do not induce a memory response.
Cross link receptors


What are cytokines?

Soluble intercellular communication factors (hormones of the immune system)
Non-antigen specific molecules (interferon)
Contribute to control of infection and development of pathology


What is an interferon?

A molecule secreted by a virus infected cell that interferes with the viral replication in bystander cells.
Th1 type acTivates B cells


How are the T helper cells antagonized?

Mutual antagonism between the 2.
IL-4 downregulates Th1 cells
IFNgamma (interferon) suppresses the activity of Th2 lymphocytes