IMMUNOGENS AND ANTIGENS

define an antigen

any molecule able to specifically interact with an immune system component

what are the 2 types of antigens

Haptens

Immunogens

define a hapten

any molecule that can interact with the immune system, but by itself cannot stimulate an immune response

which antigen types are immunogenic

haptens → non immunogenic

immunogens → immunogenic

define an immunogen

any molecule that can stimulate an immune response

define immunogenic

able to stimulate an immune system response

explain posion ivy as an example of antigens

urushiol is the oily sap in poison ivy that is an allergen

it consists of mainly catechol molecules

catechol molecules must combine with skin molecules to be able to stimulate ER

define an epitope

the tiny part of an antigen that is recognised and/or interacts with the immune system

what is an epitope also known as

antigenic determinant

how many epitopes do antigens have

they can have one or multiple

what are carrier molecules

large immunogenic molecule to which hapten or other non -immunogenic, epitope bearing, molecule may attach so that it becomes immunogenic

explain haptens in terms of medication

prescribed medication molecules are too small on their own but if they bind to a larger molecule in the body then an unintentional immune response may be stimulated

what are some examples of bacterial immunogens

whole organisms

exotoxins

specific molecules from specific organisms (e.g. haemolysins, enterotoxin, DNases)

why are exotoxins more antigenic than endotoxins

generally due to exotoxins having a more complex structure than endotoxins

how are exotoxins used in public health

they can be made into toxoids for vaccines

what are the 4 major antigen classes

polysaccharides

proteins

lipids

nucleic acids

what are some example polysaccharide antigens

ABO blood antigens

teichoic acid on bacteria

describe the immunogenicity of lipids and nucleic acids

they are rarely immunogenic on their own

couple with a protein carrier to become immunogenic

explain ‘foreignness’ as an immunogenicity requirement

discusses self vs non self

the more foreign a molecule is, the more immunogenic

explain ‘molecule size’ as a requirement for immunogenicity

the larger the molecule, the more immunogenic

describe the size boundaries of immunogens

<1000 Da = too small

>6000 Da = large

1000-6000 = grey area

explain ‘susceptibility to antigen processing and presentation’ as a requirement for immunogenicity

it primarily applies to protein molecules

the better the antigen can be processed and presented, the more immunogenic

however, note not all antigens need processing

what form of antigen to B cells recognise

they recognise the native antigen

what form of antigen do T cells recognise

they recognise the processed antigen

what are the 3 types of epitopes

sequential/linear epitopes

conformational/discontinuous epitopes

hidden epitopes

describe a sequential/linear epitope

binding to a particular amino acid sequence

how can a sequential/linear epitope be altered

nucleic acid changes may lead to altered may lead to altered amino acid sequence

this may inhibit antigen binding

describe a conformational/discontinuous epitope

it relies on 3D structure and location of target amino acid residues within the structure

How can a discontinuous/conformational epitope be altered

change in shape of whole target molecule may prevent antigen binding

describe hidden epitopes

it is when a structural change in the 3D shape of a molecule results in the epitope location being hidden

this means molecules with a binding site for the original epitope can no longer bind

what are 3 factors that can influence immunogenicity

genetic make up

dose / # of doses of antigen

administrative route

what component of genetic make up is influential

MHC genes

how is dosage/number of doses influential

increased dosage/number of doses will increase immune response

how is administrative route influential

it determines what elements of the immune system are present

list the administrative routes

IM → intramuscular

SC → subcutaneous

IV → Intravenous

IN → intranasal

Oral

how are adjuvants linked to immunogenicity

mixing an adjuvant with an antigen will increase the immune response to the antigen

define an adjuvant

a substance, drug, or treatment that helps improve, boost, or support the effectiveness of a main ingredient or primary medical treatment

describe cross reactivity

when a molecule has similar antigenic appearance to the original molecule that stimualted an initial immune response

what are the outcomes of cross reactivity

can be beneficial → use the knowledge in vaccinations

can be detrimental → autoimmune reactions

explain cross reactivity using Streptoccoccus pyogenes as an example

the variable region of host antibodies is made to react with the streptococcus antigen epitope

cardiac muscle in the host may be similar enough in antigenic appearance

this causes the antibody to bind to the host cardiac epitope and cause rheumatic fever