Antigens

What does it mean to be immunogenic?

1. Able to induce an antibody response on its own and/or 2. Able to induce a cell-mediated immunity (CMI) response on its own *not all bacteria are immunogenic. Consider the flora in our gut for instance.

3 major categories of antigens (Ag)

1. Autoantigen - a self Ag (autologous) 2. Alloantigen - an antigenic difference within a species (allogeneic). My antigens vs. my brother's antigens 3. Xenoantigen - an antigenic difference between species (xenogeneic) - traditional antigen from bacteria, etc.

What conditions improve the immune response?

1. Increased exposure time to antigen 2. Immunogens bound to proteins or that are themselves proteins - helps recruitment of both B and T cells 3. Larger, more complex antigens

What defines an antigen?

1. foreignness (greater phylogenetic differences = better response) 2. molecular size (bigger = better response) 3. chemical composition (complexity). So, homopolymers are not good immunogens. 4. Susceptibility to Ag processing/presentation

Epitope

Antigenic determinant. A given Ag usually has multiple epitopes.

T-cells respond to what type of epitope?

Epitope can be anywhere in the protein, including internalized. Reason = T cells receive antigens that have been chopped up, so what was inside the protein is no longer on the inside) Note: epitope must -be sequential -between 8-18 a.a -Ag must interact with T-cell receptor and MHC

B cells respond to what type of epitope?

External epitope. Can be sequential or non-sequential (conformational or discontinuous - refers to shape and where sequences are relatiave to one another)

When haptens are conjugated to carrier proteins, they will stimulate B cell response? T/F

F. Doesn't always occur.

How does dosage and route of antigen intake affect response?

High and low doses generally don't illicit responses. So, IV and SC routes of antigen administration usually don't illicit as good of a response as IM. Antigens ingested orally can tolerize (i.e stimulate anergy/tolerance)

Which form, D or L, of amino acids is able to be degraded for presentation?

L forms.

Adjuvant

LEADS TO STRONGER IMMUNE RESPONSE 1. compound that, when mixed with immunogens, helps make immunogens more immunogenic 2. Doesn't bind to immunogen 3. Can't make haptens immunogenic

What 2 types of substances are poor immunogens?

Lipids (act as happens when attached to proteins) and nucleic acids (can be immunogenic if attached to protein) *anti DNA antibodies CAN be made

Second most immunogenic substances?

Polysaccharides

Types of antigens include

Proteins, polysaccharides, lipids, and nucleic acids

What are often the most potent immunogens?

Proteins. Normal activator of CMI.

Immunogenicity scale

Single amino acids won't be recognized by antibodies. Complex proteins are best recognized.

Types of immunogenic molecules

T-cell independent (thymic independent ): antigen that illicit immune response without activating T-cells. Mostly B-cell response. No memory cells are made. Mostly proteins or carbohydrates. T-cell dependent: Best response. Antigens illicit both T-cells and B-cells. Generates immunological memory. Mitogens: Polyclonol (i.e non specific) activators of T and/or B cells. Ex. LPS. For B cells, they are thymic-independent antigens.

What's an antigen?

any molecule that can interact with the products of the immune response This includes interaction between a receptor (Ab or T-cell receptor) and a ligand (antigenic epitope)

Immunodominant epitope

epitope capable of inducing a more pronounced immune response immunodominant epitopes are usually those that stimulate early (and often the best) responses

What types of substance are not usually immunogenic?

lipids and nucleic acids are usually not immunogenic (we dont respond to these because they are very similar to what we have in our own bodies)

Hapten

small molecules that are antigenic (foreign) but not immunogenic. -univalent (until bound to carrier) -often need to be attached to a carrier to become immunogenic

Polysaccharides (carbs) are sometimes immunogenic. When?

when attached to proteins (glycoproteins), lipids (glycolipids) or when associated with cells (e.g. ABO blood groups)

Is the strength of binding between an antigen and a receptor important in activating an immune response?

yes

How do adjuvants work and why are they used?

Used to improve immune response to vaccines. 1. Increase half-life of immunogens 2. Improve presentation of co-stimulation of antigen-presenting cells to T-cells 3. increase production of cytokines by stimulating Toll-like receptors (TLRs) on antigen-presenting cells APCs