chapter 16 immune system- Adaptive Immunity

innate immunity

present at birth

immediate

nonspecific

Adaptive Immunity

develops after exposure to antigen

slower

higly specific

memory response - involve in immunizations

two types of adaptive immunity

humoral and cell mediated

humoral immunity

antibodies produced

B cells

plasma and memory cells

cell-mediated immunity

team of t cells

direct cell killing

intracellular pathogens

important for viral infections

kill infected cells

What type of cell is a B cell?

A lymphocyte

What do B cells differentiate into?

Antibody-producing plasma B cells

When do B cells encounter antibodies?

When they encounter an antigen

What is the role of plasma cells?

To produce antibodies

antibody

host defense protein produced in response to foreign structures, circulates in the bloodstream

What is cell-mediated immunity?

A type of immunity that involves T cell lymphocytes.

What do helper T cells do?

They stimulate B cells.

What do cytotoxic T cells do?

They kill infected host cells.

Antigen

molecules that elicit the production of antibodies

-can exist in a singular structures

Epitope

A small segment of antigen that can elicit an immune response

-can have more than one in this

haptens

very small molecule that must bind to another immunogen in order to be recognized

-alone will not, not large enough, must be bound to another large immunogen

APC and examples

antigen-presenting cell

ex: dendritic cells, B cells

What does antigenicity measure?

How well antigens elicit an immune response.

What is the threshold for each antigen?

The just right amount of antigen required to generate the best response.

What happens with low antigen levels?

They only activate a few B cells.

What can high antigen levels lead to?

Peripheral tolerance.

order of proteins, carbohydrates, and nucleic acids; lipids in immune response

1. proteins= vairety

2. Carbohydrates - dont really stimulate immune response

3.nucleic acid lipids

What is immunological specificity in adaptive immunity?

Antibodies are generated for specific antigens.

Can antigenetically related organisms provide immune protection against each other?

Yes, some antigenetically related organisms may generate immune protection against each other.

Which two viruses are known to provide cross-protection due to immunological specificity?

Cowpox and Smallpox.

What must key virulence proteins share to allow for cross-protection?

They must share similar structures.

antibodies

-provide immunological response

-Circulate in blood and lymph can be found on surface of B cells (numeral)

antibodies consist of 4 polypeptide chains

2 long heavy chains, and I short light chains

Two identical antigen-binding sites

variable and constant regions

Five classes of antibodies determined by heavy chain

IgM, IgA, IgG, IgE, IgD

Heavy chain constant regions play a role in

function of antibodies

heavy chain of all IgA is the same but different of IgG

same structure different heavy chain

Isotype

different antibodies of species

allotype

antibody differences between individuals of a specie

Idiotype

different antibodies within an individual (depends on antigen)

What is the most abundant antibody in blood and tissue fluids?

IgG

What is one function of IgG?

Opsonizes microbes to improve phagocytosis

How does IgG interact with viruses?

Neutralizes viruses

What pathway does IgG activate in the complement system?

Activates the classical pathway

What is a unique characteristic of IgG regarding the placenta?

IgG can cross the placenta

can be good and bad

IgD

commonly found on Surface of B cells

IgE

mainly found on surface of most cells and basophils

Allergic Responses

IgA

secretory antibody that is secreted across mucosal surfaces

-dimer held together by chain; found in tears, Saliva, breast milk

IgM

often circulates

Ferris wheel shaped pentameter

usually first antibody detected

heavy chains

monomers

IgM -> IgG

A more efficient antibody very adapted

What is the primary antibody response?

Antigen binds to B cells that only make antibodies against that antigen, primarily producing IgM.

What happens to B cells during the primary antibody response?

B cells proliferate and differentiate into antibody-secreting plasma cells and memory B cells.

What type of antibody is produced first in the primary response?

IgM is produced first.

What is the eventual class switch in antibody production after the primary response?

The class switch is to IgG.

How does the abundance and efficiency of IgM compare to IgG?

IgM is abundant but not efficient compared to IgG.

Some activated B cells become

memory cells

memory cells that encounter antigen again quickly trigger

secondary antibody response

Immunization

Exposure

-vaccine or natural memory cells created allow for a rapid response when the pathogen is encountered again

B cell receptors

-Found on B cells to help identify correct antigen

-Typically have IgD or IgM

-may be 50, 000 receptors specific for the same antigen

-can be coded to produce antibodies for certain antigen

How can B cells be activated?

B cells can be activated in two ways: T cell independent and T cell dependent.

What is T cell independent activation of B cells?

B cell receptors bind antigen with multiple copies of epitope, resulting in capping.

What is T cell dependent activation of B cells?

Antigen binds to B cells; CD40 ligand on T cells binds to CD40 on B cell surface.

capping

cluster binding of B cell receptors on B cell

capping

cluster binding of B cell receptors on B cell

cd4o

receptor on T cell

What is the role of T cells in the immune system?

T cells are critical to directing and balancing the immune system.

What are the two groups of T cells based on differentiation proteins?

Helper T cells and Cytotoxic T cells.

What surface protein do Helper T cells display?

CD4 antibody.

What surface protein do Cytotoxic T cells display?

CD8.

What type of immunity do Helper T cells mediate?

Cell-mediated immunity.

What type of immunity do Cytotoxic T cells mediate?

Cell-mediated immunity only.

cytotoxic

kill cells

coreceptors mediate how

T cells recognize antigen

How T cell recognize

T cell activation is dependent upon antigen presenting cells (APC's

-T cell only recognize antigens presented on MHCs

What is the function of Class I MHC?

Class I MHC are found on all nucleated cells (not RBC).

Where are Class II MHC found?

Class II MHC are found on antigen presenting dendritic cells, macrophages, and B cells.

How T cells recognize antigens

Antigen made by intracellular pathogens (endogenous antigens)are presented on MHC1 molecules

↳ results in destruction of infected cell

-By CD8 T-cells

-Antigen produced outside of the APC(exogenous antigens)are engulfed and attach to MHC2 molecules

↳ results in antibody production

What do T cell receptors (TCRs) bind to?

Antigens

Where are T cell receptors (TCRs) located?

On the surface of T cells

What must antigens be attached to for TCRs to bind?

MHC proteins on APCs

What complex do T cell receptors (TCRs) form with CD3?

CD3 complex

What do CD3 proteins do when activated by TCRs?

Signal the nucleus and trigger proliferation of the T cell

What is the role of CD4 in activating cells?

binds to MHC II/antigen complex.

What is the role of CD8 in activating cells?

binds to MHC I/antigen complex.

What is the second signal required for T cell activation?

CD28 on T cell binds to B7 on APC.

B7

ligand

helps activate T cells

T cell must be able to recognize and differentiate self from nonself

process of selection

-learn to recognize in thymus

regulatory cells

negative selection that survived

positive selecton of t cell

t cells that weakly recognize self are allowed to live

-weak response to antigens, enter peripheral self

negative selection of T cells

t cells that bind to strongly to self are destroyed

- go through apoptosis

Some self-reactive t cells live and become

Regulatory T cells

-prevent autoimmune disease

-block activation of self-reactive lymphocytes

-protect from self-reactive cells

Superantigens do not

require processing and presentation by APCs

What do superantigens bind to?

Outside of T cell receptors on T cells and MHC molecules on antigen-presenting cells (APCs).

What is the effect of superantigens on T cell activation?

They can activate many more T cells than usual, with no antigen specificity involved.

How many T cells can be activated at once by superantigens?

Up to 30% T cells can be activated at once.

What can excessive T cell activation by superantigens lead to?

A cytokine storm.

What type of immunity is mediated by Cytotoxic T cells?

Cell mediated immunity

What must Cytotoxic T cells bind to for activation?

Antigen presented on APCs via MHC I molecule

Which cytokine is required for the activation of Cytotoxic T cells?

IL-2 produced by Th1 helper cells

What do activated Cytotoxic T cells do after leaving the lymph node?

They travel to the site of infection to kill infected cells

What type of pathogens are Cytotoxic T cells important for clearing?

Intracellular pathogens

Which cells express MHC I molecules?

All nucleated cells

What process do Cytotoxic T cells induce in infected cells?

Apoptosis

induce apoptosis

perforin

granzymes

perforin

create pore in host cell