بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor...

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Transcript of بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor...

Page 1: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

بسم الله الرحمن الرحيم

Page 2: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Antigen

Samira Rajaei, MD, PhD.Assistant professor

Department of ImmunologyTehran University of Medical Sciences

Page 3: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Antigen definition

Antigen Anti(body)+ generator

• Antigen

• Immunogen

• Tolerogen

Page 4: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Which cells are the main players of adaptive immunity?

Page 5: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Any substance that may be specifically recognized by an antibody molecule (BCR) or T cell receptor

(TCR)

Antigen

Page 6: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Antibodies can recognize as antigens almost every kind of biologic molecule: Lipids Carbohydrates Proteins Nucleic acids

TCRs mainly recognize peptides

Difference between Ag recognition

Page 7: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Immunogen

Antigens are capable of activating lymphocyte

Page 8: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

All antigens are recognized by specific lymphocytes ① true ②falseAll antigens are capable of activating lymphocyte① true ②false

True/False

Page 9: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Foreign antigens may be administered in ways that preferentially induce tolerance rather than immune responses.

These antigens are tolerogen.

Tolerogen

Page 10: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Small chemicals (dinitrophenol) may bind to antibodies, and are therefore antigens, but cannot activate B cells on their own (they are not immunogenic)

Hapten

Page 11: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Immunogenicity

Foreignness Molecular sizeChemical structure

complexityDosage, Route, individual difference, timing of

administration

Page 12: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Foreignness is essential to immunogenicity

Self-responsive cells are eliminated during lymphocyte ontogeny

More Foreignness; more immunogenicity

Foreignness

Page 13: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

>100000 Dalton <10000 Dalton

Molecular size

Page 14: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Composition Proteins (most potent) Polysaccharides (second potent) Nucleic acids and lipids (are not immunogenic

unless …) Chemical complexity

Homopolymrs of amino acids? Which one of protein structures are more

immunogen? More complex molecules are more immunogen

Chemical structure complexity

Page 15: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

High doses of immunogen may cause a lack of responsiveness (tolerance)

Intermediate doses of immunogen are generally the best immune response inducers

Low doses of immunogen may not induce immune responses

Dosage

Page 16: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Route of administration influences which cells (and how many of them) are stimulated s.c. (subcutaneous) i.d. (intradermal) i.m. (intramuscular) i.v. (intravenous) Oral administration i.n. (intranasal)

Route of immunogen administration

Page 17: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

How to generate antibody against

haptens?

Page 18: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

attach them to a protein before immunization which is called carrier.

attaching a number of hapten molecules to a single molecule of a polysaccharide (render it multivalent)

Hapten+Carrier

Page 19: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

An adjuvant is any substance that enhances the immunogenicity of substances mixed with it

Many adjuvants in experimental use are microbial products, such as killed mycobacteria and LPS, that engage TLRs

What are the differences between Adjuvant and carrier? do not form stable linkages with the immunogen adjuvants are needed primarily for initial immunizations,

whereas carriers are required to elicit not only primary but also subsequent responses to haptens.

Adjuvant

Page 20: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Soluble : (proteins , polysaccharides) + Adjuvants

Particulate: bacteria, virus and RBCs (Adjuvants are not necessary)

Colloidal (non robust immunogens)

Physicochemical structure of Antigens

Page 21: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Delayed release of antigens Adjuvants convert soluble protein antigens into

particulate material, which is more readily ingested by antigen-presenting cells such as macrophages

adjuvants activate dendritic cells to express more MHC, increase the expression of costimulators, and cytokines needed for T cell activation, stimulate migration of the dendritic cells to lymph nodes .

How adjuvants enhance immunogenicity of proteins?

Page 22: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Freund’s adjuvant Incomplete (oil in water emulsion) Complete (oil in water emulsion and dead

mycobacteria)

Alum (aluminum hydroxide or aluminum phosphate)

Types of adjuvants

Page 23: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.
Page 24: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Epitope/Determinant

Macromolecules (proteins, polysaccharides, and nucleic acids) are usually much bigger than the antigen-binding region of an antibody molecule

Any antibody binds to only a portion of the

macromolecule, which is called

a determinant or an epitope

Page 25: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Most of the macromolecules have multiple determinants.

Page 26: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Polyvalency/multivalency

The presence of multiple identical determinants in an antigen is referred to as polyvalency or multivalency. Polysaccharides nucleic acids

Surface of microbs Polyvalent antigens can induce

clustering of the B cell receptors and initiate the process of B cell activation

Page 27: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Globular proteins

Most globular proteins do not contain multiple identical epitopes and are not polyvalent

Proteins could not cross link the B cell receptors.

They need the help of T lymphocytes. Proteins are T-dependent antigens.

Page 28: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Nonoverlapping determinants 2 or more antibody bind to a protein antigen No steric interference

Overlapping determinants Steric interference

Spatial arrangement of epitopes

Page 29: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Allosteric effects (conformational changes positively or negatively effects another antibody binding without Steric interference)

Allosteric Effects

Page 30: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Epitopes formed by several adjacent amino acid residues are called linear determinants.

The antigen-binding site of an antibody can usually accommodate a linear determinant made up of about 6 amino acids.

If linear determinants appear on the external surface or in a region of extended conformation in the native folded protein, they may be accessible to antibodies

More often, linear determinants may be inaccessible in the native conformation and appear only when the protein is denatured.

Linear determinants

Page 31: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Conformational determinants are formed by amino acid residues that are not in a sequence but become spatially juxtaposed in the folded protein.

Conformational determinants

Page 32: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Proteins may be subjected to modifications such as glycosylation, phosphorylation, ubiquitination, acetylation, and proteolysis.

Modifications produce new epitopes.

Neoantigenic determinants

Page 33: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.
Page 34: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

T lymphocytes recognize linear peptide determinants in combination with MHC residues.

Epitopes determined by T cells

Page 35: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

These molecules are able to bind to TCR complex and CD2, causing them to cluster on the cell surface, thereby mimicking the clustering caused by antigen presentation.

They activate the T cells regardless of their antigen specificity. Phytohemagglutinin (PHA), a lectin Concanavalin-A

Mitogens

Page 36: بسم الله الرحمن الرحيم. Antigen Samira Rajaei, MD, PhD. Assistant professor Department of Immunology Tehran University of Medical Sciences.

Molecules that can activate T cells non-specifically

Superantigens bind to MHC class II molecules on APCs and are recognized by TCRs, but not in the same way as an MHC molecule-peptide complex.

Binding is to the Vβ chain of the TCR Staphylococcal enterotoxins Toxic shock syndrome toxin

Superantigens