General characteristics of Antigens Flashcards by Mary Doody

Entry of antigens into the body

By the skin and mucus membranes- tissue damage

Cytokines and leucocytes are at the site of injury

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ASF= African Swine Fever, and why is it so serious?

50 proteins on the surface

The neutralization part is hidden- cannot be found by the immune system- so no AB’s are produced against it

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3 Characteristics of the antigen

Immunogenicity
Tolerogenicity
Antigenicity

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Immunogenicity

Ability of a molecule to elicit an immune response– effector cells and antibodies

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Tolerogenicity

Ability of antigen to prevent immune response

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Antigenicity

Ability of molecule to be identified by Atg recognising immune cells

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What are the 2 most important components of the antigen?

Carrier

Epitope (where the ab binds)

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Specificity of the antibodies

Specific for the carrier
Specific for the epitope
Specific for both the carrier and the epitope

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Cross-reactivity

When there is similarity between the epitops- but not the very same
Used in vaccinations e.g turkey herpes virus as vaccine for Marek’s disease
TB- M. Bovis and M. Avium

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Factors Influencing Immunogenicity

Immunogen
Biological System
Epitope
Method of admin

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Factors Influencing Immunogenicity: Immunogen

Foreignness- how many non-self epitopes- usually correlates with size! Also, remember D-aa is not in mammals
Size- larger, more epitopes, may be spaced further apart
Chemical: Proteins: tertiary are the strongest
Polysaccharide: rare- glycoprotein
NA: rare
Lipids: NONE
Degradability

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Factors Influencing Immunogenicity: Epitope

Composition- aa sequence, the longer and more complex the better e.g Gly polymer not immunogenic
Structure
linear- necessary for T-cells
conformation- B-cell
Number
many of the same or of different epitopes
accessibility e.g hidden epitopes

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Factors Determining Antigenicity

Biological factors
Route of admin
Quantity of antigen
Antigen competition- polyvalent vaccines
Adjuvants- immunostimulation- depot effect
Antigen type- T dependent/independent

+cultures can be infected by non-pathogenic viruses

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Factors determining antigenicity: Biological factors

Here there are huge individual differences 
Genetic factors- MHC, TCR, BCR
Age- too young, too old 
Condition
Keeping 
Feeding

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Factors Influencing Immunogenicity: Route of admin

Parenteral vs enteral

Oral tolerance vs oral vaccination

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Factors Influencing Immunogenicity: Quantity of antigen

No effect or tolerated

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Factors influencing the effect of the Atg: Booster effect

2nd dose of the vaccine generates a stronger immune response than the first, this is due to the immunological memory and B and T cells i.e the acquired immune response

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Factors Influencing Immunogenicity: Adjuvant

Any substance than when given with an antigen, it enhances the immune response to that antigen.
Negative side effects:
-prolong the presence of the antigen
-inflammation
-activate innate immune system- complement cascade and phagocytosis

What are the 3 possible ways of recognition

Pathogen/Non-self:
- markers and metabolic products of microorganisms
- PAMP
Missing self
- self markers on the surface of normal cells, which can block the immune response
Altered self
- markers not resembling healthy self-markers

Visible self

Antigens of the body that are tolerated

Invisible self

Antigens that are not tolerated but are ignored under normal circumstances

Visible non-self

This is what the immune system usually reacts with

Invisible non-self

Non-self antigens that are not reacted with

2 main functions of the immune system

Attacks foreign (non-self)
Tolerates self
(the body is self and the rest of the universe is foreign)

What are the 2 things necessary for an immune response to occur?

Pathogen | Danger

Stranger model of the immune response

Pathogen-- PAMP3 and these bind to the PRR on the dendritic cell Dendritic cell maturation- a peptide MHC complex seems to appear CD60 and/or CD86 co-stimulatory molecule Then this dendritic cell migrates to the lymph nodes and the TCR of a T-cell binds to the MHC

Danger model of the immune response

Necrotic cell death Stimulates the release of DAMP's and these then bind to the DAMP receptor of the Dendritic cell From here it is the same as the stranger model DAMP= damage associated molecular pattern

What is the Pathogen-Associated Molecular Pattern (PAMP)

Exogenous molecular patterns that can activate the non-specific immune response It's receptor consists of specific proteins on the surface that react with the antigens

PAMP and gram (+)

**Lipotechoic acid Lipoprotein Peptidoglycan

PAMP and gram (-)

**LIPOPOLYSACCHARIDE (how they recognise it is foreign) Lipid A Porin Peptidoglycan (much thinner than gram (+))

PAMP and acid-fast

**Mycolic acid Porin Galactan Peptidoglycan (thin)

Some other examples of PAMP

``` LPS of gram (-) is NB Lipoproteins Peptidoglycan layer Mannose, dextrose Flagellin Haemaglutinin ```

DAMP (damage associated molecular pattern) can be

Extracellular and intracellular

Some examples of DAMPs

``` Hyaluronic acid is NB!!! Heat shock protein DNA Fibrinogen Cholesterol ```

What are the 2 basic types of receptors

1. Pattern Recognition Receptor (PRR) - can bind to PAMP or DAMP - can be on the surface or in the cytoplasm 2. Opsonin Recognition Receptor (ORR) - opsonins

The types of ORRs

Fc receptors Complement receptors Lectin receptors (mannose)

The types of PRRs

``` Scavenger receptor (SR) Mannose receptor (MR) LPS receptor (CD14) **Toll-like receptor (TLR) NOD-like receptor (NOD1, NOD2) Retinoic acid inducible gene (RIG)-like receptor ```

LPS receptor (CD14) ligand and action

Ligand: LPS Action: removal of microbes and induction of inflamm cytokines (for recognition)

Toll-like receptor (TLR) ligand and action

Ligand: Pathogen patterns on the cell surface or the endosome Action: Signal to adaptive immune system

NOD-like receptor (NOD1, NOD2) ligand and action

The peptidoglycan layer on gram (-) and acts in the CYTOSOL Action: Inflamm IL-6, IL-12, TNF apoptosis- IL-1

Scavenger Receptor (SCAR)

Scavenger= animal/organism that feeds on organic dead matter-- FUNGI are NB Are macrophage receptors that recognise low density lipoprotein (LDL) elements of the bacterial cell wall and eukaryotic cell membrane

Mannose Receptor family, location and action

Location: Macrophages Immature DC Endothelial, epthelial and Kuppfer cells Action: Recognition of carbohydrates of pathogens

Nod-like receptors (NLR) more specifically

NOD: Nucleotid-binding oligomerization domain React to microbial intracellular PAMPs NOD1: peptidoglycans---> IL-1, IL-8 NOD2: muramyl dipeptide---> defensin NOD3: viral NA, silica

RIG-Like receptor

RIG: Retinol acid Inducible Gene Action: - Viral dsRNA detection - Capsase activation - Trigger the production of IFN-1