Chapter 2 Flashcards by Christina Johnson

Immunogen

macromolecules capbale of triggering an adaptive immune response by inducing the formation of antibodies or sensitized T cells in an immunocompetent host
can specifically react with antibodies or sensitized T cells

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Antigen

a substance that reacts with an antibody or sensitized T cells but may not be able to evoke an immune response in the first place

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Relationship of immunogen to antigen

Immunogen = antigen; antigen =/= immunogen

Immunogen is basically a type of antigen; angiten is a broader term

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Biological properties of an individual that influence the immune response

age (middle aged = best)
overall health (nourishment/fatigue/stress) 
dose (quantity of immunogen)
route of inoculation (IV, ID, SubQ, oral) 
genetic capacity (MHC)

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Immunogenicity

the ability of an immunogen to stimulate a host response
depends on macromolecular size, foreigness, chemical composition/molecular complexity, ability to be processed and presented with MHC molecules

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Immunogenicity characteristics

molecular weight - the bigger the beter (response)
foreigness - allows distinguishing self from nonself
chemical composition/chemical complexcity - longer/larger chains of proteins/amino acids (more complex shapes)
ability to be processed - must be degraded and presented to MHC to create a response

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Epitope

key portion of the immunogen (determinant site)

molecular shapes or configurations that are recognized by B/T cells

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Linear/conformational epitope

LE - (sequential) amino acids following one another on a single chain
CE - One+ chains folded to make linear and conformational epitopes

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Antigen-presenting cell (APC)

cell that degrades and presents immunogens for immune response

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Haptens

nonimmunogenic materials that, when combines with a carrier, create new antigenic determinants
small substances that cannot create a rxn on their own
categorized as antigens (not immunogens)
hapten + carrier = precipitation and agglutination reaction

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Examples of haptens

Catechols (H) (poison ivy) + tissue proteins of skin -> rxn of skin
Penicillin (Normal body proteins + hapten)

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Adjuvant

a substance administered with an immunogen that increases the immunce response in order to provide immunity to a particular disease help make immunization more effective protect immunogens from degradation + allow a longer response time (larger immune response)

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Autoantigens

antigens that belong to the host do not evoke an immune response under normal circumstances

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Autoimmune Disease

when autoantigens become self reactive to the body

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Alloantigens

antigens from other members of the host’s species and are capable of eliciting an immune response important to tissue transplantation and blood transfusions

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Heteroantigens

antigens from other species (other animals, plants, or microbes)

Heterophile anitgens

heteroantigens that exist in urelated plants or animals but are either identical or closely related in structure so that antibody to one will cross-react with antigen of the other
(blood group A/B antigens and bacterial polysaccharides)

SRBCs

Sheep red blood cells important to the development/study of heterophile antigens

MHC location and function

located on all nucleated cells in the body
function in determining self/non-self, can function as antigens, activate T cells
once called HLA - Human Leukocyte antigens

MHC system

most polymorphic system found in humans

- code for proteins immune recognition/ diverse immunogens

MHC gene coding

found on short arm of chromosome 6

- 3 categories/ classes

MHC class 1

found at 3 loci; A,B,C

- only one gene coding for each particular molecule

MHC Class 2

found in the D region
loci are DR,DQ, DP
one gene codes for alpha chain; 1+ gene(s) code for beta chain

MHC Class 3

Found between Class 1 and class 2 regions on chromosome 6

- codes for C4A, C4B, C2, and B complement proteins, Cytokines and tumor necrosis factor

Roles of MHC classes

MHC class 1 and 2 - involved in antigen recognition (influence the antigens Tcells respond to) MHC class 3 - secreted proteins that have an immune function (not expressed on cell surfaces

Alleles

alternate forms of a gene that code for slightly different varieties of the same product

Polymorphic system (MHC)

many possilbe alleles at each location at each loci (HLA-A) 2,013 (HLA-B) 2,605 (HLA-C) 1,551 Low probability that 2 individuals will express the same MHC molecules

characteristics of MHC genes

- codominant (all alleles expressed) - Haplotype inheritance (closely linked, genes inherited together) - each inherited chromosomal region has a package of genes for A,B,C,DR,DP,DQ - One haplotype inherited from each parent

expression of MHC class 1

- on all nucleated cells - highest on lymphocytes and myeloid cells - low/undetectable on liver hepatocytes, neural cells, muscle cells and sperm

Structure of Class 1 MHC molecules

Glycoprotein dimer of two noncovalently linked polypeptide chains alpha chain (heavier), folded into 3 domains, inserted in the cell membrane, hydrophobic Beta 2- microglobulin (lighter) encoded by one gene on chromosome 15 (not polymorphic) (this is the same in every Class 1 molecule, essential for folding of alpha chain, no cell membrane penetration

expression of MHC class 2

found on APCs (B lymphocytes, monocytes, macrophages, dendritic cells, thymic epithelium)

Structure of Class 2 MHC molecules

DP,DQ,DR - 2 noncovalently bound polypeptide chains (heterodimers) DR expressed the most (accounts for 1/2 of all Class 2 molecules) DR beta - most highly polymorphic

Antigen presentation

process by which degraded peptides within cells are transported to the plasma membrane where T cells can then recognize them

MHC classes present to which T cells

Class 1 molecules peptides synthesized withine the cell to CD8 T cells (viral, tumor, parasitic antigens) Class 2 molecule present exogenous antigen to CD4 T cells (bacterial infections, extracellualr pathogens)

Class 1 MHC-peptide interaction

Endogenous pathway of antigen presentation synthesized in ER and bind peptides from where they are bound on the ER forms a complex and moves to the cell surface where it can be recognized by T cells CD8+ T cells produce cytokines that cause lysis of the entire cell

Proteasomes

large cytoplasmic complexes of the proteases cleave peptides for delivery to class 1 molecules

Transporters associated with antigen processing

proteins responsible for ATP-dependent transport of peptides to class 1 molecules most efficient with 8-16 amino acids in size

Class 2 MHC - peptide interaction

synthesized in ER (+invariant chain), transported to endosomal compartment where they can bind to peptides binds to peptides of 13-18 amino acid residues once bound, molecule is transported to cell surface for recognition by T cells CD4+ recruits and triggers B-cell response

Clinical importance of MHC molecules

``` Ankylosing spondylitis Celiac disease Rheumatoid arthritis Type 1 diabetes (autoimmune diseases) Vaccine sensitivity ```