Antigens and antigen presenting cells

Where are cytokines produced?

Cytokines are produced by many cell types.

Dendritic cells, Macrophages, B cell. Antigen capture

Dendritic cell = multiple Macrophage = Multiple B cell = Only by BCR

pH endosomes vs lysosomes vs phagosomes

Endosomes = 6.8 Lysosomes = 5.5 Phagosomes = 5.5

Exogenous antigen processing vs endogenous antigen processing

Exogenous - Extracellular pathogen - Processed via endocytic pathway - processed antigens presented on MHC class II molecules on APC surface. - CD4+ TCR recognises antigen - Antibody production and CD4+ Th1 enhanced (cellular and immune responses) Endogenous - Intracellular pathogen - Processed via cytosol and proteasome - Processed antigens presented on MHC class I molecules on APC surface - Cell mediated immunity enhanced e.g CD8+ cytotoxic T lymphocytes. Cytokines are secreted in both exogenous and endogenous processing once the antigens have been recognised by T cells.

For which type of pathogens is variation, dift and shift particularly important?

Extracellular pathogens and their surface antigens - antibodies are the primary defence.

Carrier

Foreign proteins to which small non-immunogenic molecules (haptens) can be coupled to stimulate an immune response. Self proteins such as albumin can also serve as carriers e.g allergy to drugs.

Example of pathogen shift

Haemagglutinin of influenza virus.

Cytokine produced from proliferated T cells that stimulates macrophage activation

IFN gamma

Cytokine clinically important in asthma and eosinophil activation

IL-13

Cytokine produced from activated T cell upon binding with APC in the adaptive immune response.

IL-2

Immune response to antigenic drift

Immune response is partially but not fully protective. - Subtle variation in protein so some antibodies bind giving partial protection. - No antibodies recognise drifted epitope.

Immune response to antigenic shift

Immune response ot protective. - Two virus strains circulating in same host - Major variation in protein - No antibodies recognise shifted protein

Entry into cells. Inactivated vaccine vs modified live vaccine.

Inactivated vaccine = Phagocytosis / endocytosis / sIg binding. Modified live vaccine = Direct entry into cytosol.

Intracellular pathogen vs extracellular pathogen

Intracellular - Antigen = virus / bacterium - Processing = endogenous - MHC class I restricted - T cells involved = CD8+ (cytotoxic T cells) - Predominant outcome = CMI - Location = site of replication Extracellular - Antigen = virus / bacterium / parasite - Processing = exogenous - MHC class II restricted T cells involved = CD4+ (T helper cells) - Predominant outcome = Antibody - Location = site of replication.

How to determine which type of immune response willbe stimulated?

Intracellular pathogens will result in the cell mediated immune response predominating. Extracellular pathogens will result in the adaptive immune response predominating. BOTH the cell mediated and adaptive immune response will be stimulated, however, one type will predominate depending on the nature of the pathogen.

Intramuscular vs intranasal vaccines.

Intramuscular = systemic Intranasal = local (mucosal)

Use of lectins

Lectins offer a way for molecules to stick together without getting the immune system involved, which can influence cell-cell interaction.

Cytokines

Low molecular weight soluble proteins, that bind to cell surface receptors and provide signals that can result in a number of outcomes.

In the naive animal, where is the immune response generated?

Lymph nodes at the draining site of where the antigen exposure was.

MHC type associated with... Dendritic cell, Macrophage, B cell

MHC class II

Consequences of pathogenic drift

Mild epidemic occurs as degree of cross protection still exists

Consequecnes of pathogenic variation

Multiple (consecutive) infections with the same pathogen

Is antigenic variation at a genomic level?

NO

Cytokines are induced in an antigen dependent manner (stimulus). Is the action of cytokines antigen dependent also?

NO, the action of cytokines is antigen Independent.

Locations where immune response started. Naive vs primed.

Naive = Lymph nodes draining site of antigen exposure. Primed = Local site of antigen exposure

Lymphoid tissue involed. Naive vs primed.

Naive = Lymph nodes, spleen Primed = MALT (e.g GALT, BALT)

Immune response time. Naive vs primed.

Naive = slow (>3 days) Primed = Fast (1-2 days)

Are all cyotkines secreted?

No, most are secreted but others are membrane bound.

Consequences of pathogenic shift

Pandemic occurs as population has no immunity.

Pathogen variation

Pathogen exists as multiple strains (serotypes)

Size of particles engulfed. Phagocytes vs endosomes

Phagocytes contains much bigger particles than endosomes. Endosomes contain particles 15-100nm.

Pathogen drift

Point mutations in the DNA which lead to a coding change in the amino acid. resulting in a small change in the structure of the protein.

How does antigenic shift occur?

RNA segments are exchanged between viral strains in a secondary host.

Pathogen shift

Reassortment of segments in the genome between different strains of the same pathogen leading to dramatic changes in the expressed protein. Change so radical proteins no longer recognised by the immune response causing serious disease outbreaks

Autocrine

Self signalling

Potential consequences of pathogen shift

Serious disease outbreaks as changed protein expression is not recognised by the immune response.

Endocrine

Signals to distant cells

Paracrine

Signals to nearby cells

What is required for secreted of a cytokine to occur?

Stimulation (antigen dependent). Require only picomolar concentrations to have an effect.

Cytokines involved in initiating the immune response. Th1 vs Th2

Th1 Th2 - IL-2 + + - IFN gamma ++ - - TNF alpha ++ -

Cytokines central to the production of antibody (IL-4) and antibody switching (IL-5) Th1 vs Th2

Th1 Th2 - IL-4 -- ++ - IL-5 -- ++

What dictates the type of antigen processing and presentation?

The route of antigen entry.

Antigen processing and presentation

The routes by which antigen enters a cell is processed within the cells to form peptides and these are then presented on the surface of the APC in association with MHC.

Autoimmunity

When own tissues induce an immune response.

Does the form of antigen (pathogen) dictate the type of immune response?

YES

Lectins

a type of protein that can bind to cell membranes. They are sugar-binding and become the "glyco" portion of glycoconjugates on the membranes.

Example of pathogen variation

e.g 84 serotypes of S. pneumoniae.

Example of pathogen drift

e.g Haemagglutinin and neuraminidase of influenza virus.

Severe consequences of antigenic variation, drift and shift

- Alters the antigens, therefore specific immune response no longer recognises them - Particularly important for extracellular pathogens and their surface antigens, against which antibodies are the primary defence.

Examples of Haemaglutinin

- Antibodies - Lectins

Immune response in the primed animal.

- Antigen can be captured, processed and presented locally. - Efficient - Memory cells

The 3 types of cytokine activation

- Autocrine - Paracrine - Endocrine

Dendritic cells, Macrophages, B cell. Naive or memory T cells

- Dendritic cell = Both - Macrophage = Memory - B cell = Memory

Dendritic cells, Macrophages, B cell. Naive vs primed

- Dendritic cell = Both - Macrophage = primed - B cell = primed

4 Types of antigen presenting cells

- Dendritic cells (multiple subtypes) - Macrophages - B cells - Basophils (proven only in mouse)

Life span of effector cells vs memory cells

- Effector cells short lived (days / weeks) - Memory cells long lived (months / years)

The two types of antigen processing

- Endogenous - Exogenous

Direct entry to the cytosol - type of antigen processing and example.

- Endogenous antigen processing - MHC class I restricted - e.g Intracellular pathogens

Arm of the adaptive immune response generated with an intranasal vaccine with live whole virus

- Endogenous processing - MHC class I restricted - Cell mediated immunity - Local (mucosal)

Arm of the adaptive immune response generated with an intramuscular vaccine with live whole virus

- Endogenous processing - MHC class I restricted - Cell mediated immunity (CD8+) - Systemic

Arm of the adaptive immune response generated with an intramuscular vaccine with ISCOMS containing two proteins of the pathogen

- Endogenous processing - MHC class II restricted - Cell mediated immunity (CD8+) - Systemic

Arm of the adaptive immune response generated with an intramuscular vaccine with a viral vector encoding a single protein of the pathogen

- Endogenous processing - MHC class II restricted - Cell mediated immunity (CD8+) - Systemic

B cells, APC and others present to what type of cells in response to intracellular pathogens, and the cytokines produced.

- Endogenous processing - MHC I restricted. - Presents to CD8+ T cells (cytotoxic) - CMI - Cytokines = IL-2, IFN gamma

Phagocytosis / endocytosis / binding to sIg - type of antigen processing and example.

- Exogenous antigen processing - MHC class II restricted - e.g extracellular pathogens

Arm of the adaptive immune response generated with an intranasal vaccine with inactivated whole virus

- Exogenous processing - MHC class II restricted - Antibody (CD4+) - Local (mucosal)

Arm of the adaptive immune response generated with an intramuscular vaccine with inactivated whole virus

- Exogenous processing - MHC class II restricted - Antibody (CD4+) - Systemic

Arm of the adaptive immune response generated with an intramuscular vaccine with recombinant, inert vaccine.

- Exogenous processing - MHC class II restricted - Antibody (CD4+) - Systemic

Types of pathogens that enter the cell via phagocytosis/endocytosis/ sIg binding?

- Extracellular virus or bacteria. E.g inflenza virus, ospsonised bacteria with capsules, non-encapsulated bacteria. - Inactivated virus / bacterial vaccines - Proteins

When an endogenous pathogen has entered the cell, how does genomic replication come about?

- Following uncoating, the viral genome is transported to the site of replication - RNA genome replication can occur exclusively in the cytoplasm, but genomes of DNA viruses and some RNA viruses have to enter the nucleus for replication - Mechanism for genome transport to and passage through nuclear envelope required

How pathogenic variation, drift and shift create difficulties for health/vaccine design.

- How can multiple serotypes be protected against? - Continuous surveillance of circulating strains - Repeated updating of strains in vaccines.

Cytokines in the innate immune response

- IL-1 - IL-12 - IFN gamma - TNF alpha - Chemokines

Cytokines in the innate immune response that stimulates inflammation and activates macrophages

- IL-1 - TNF alpha - Chemokines

Cytokines involved in cell mediated immunity

- IL-2 - IFN gamma

Cytokines produced from proliferated T cells that stimulates CTL differentiation

- IL-2 - IFN gamma

Cytokines produced by APC which present to CD4+ Th1

- IL-2 - IFN gamma CMI

Cytokines in the adaptive immune response

- IL-2 - IL-4 - IL-5 - IFN gamma

Cytokines produced from proliferated T cells that stimulates B cell antibody switching

- IL-2 - IL-4 - IL-5 - IFN gamma

Cytokines involved in antibody production

- IL-4 - IL-5 - IL-10 - IL-13

APC B cells presented to which T cell

- IL-4 - IL-5 - IL-10 - IL-13 Antibody produced

Cytokines produced by APC which present to CD4+ Th2 cells

- IL-4 - IL-5 - IL-10 - IL-13 Antibody produced

Types of vaccines available

- Inactivated pathogen - Modified live pathogen - Immune stimulating complexes (liposomes) - Individual purified recombinant proteins - The effect off adjuvants

Types of pathogens that enter cell directly into the cytosol

- Intracellular virus or bacterium - Pathogens DNA which results in protein synthesis - Modified live virus / bacterial vaccines - Immune stimulating complexes (liposomes).

Vaccine containing live whole virus vs vaccine containing an inactivated whole virus

- Live whole virus = endogenous, MHC I, CD8+ (CMI) - Inactivated whole virus = exogenous, MHC II, CD4+ (Antibody)

What is the MHC-peptide complex recognised by and what does this result in?

- MHC-peptide complex recognised by circulating lymphocytes. - Cytokines secreted - Adaptice immune response enhanced.

Memory cells in the immune response of the primed animal. Memory cells vs naive cells.

- More sensitive to re-stimulation by antigen on APC than naive cells - Produce cytokines more quickly - Synthesise more cytokines.

Dendritic cells ability as APCs

- Non specific macropinocytosis (engulfment of large volumes of surrounding fluid) - Phagocytosis - Efficient with soluble antigens from extracellular fluid

Pathogen drift vs pathogen shift

- Pathogen drift = point mutation = small change in protein - Pathogen shift = Reassortment of genomes = Radical change in protein

Macrophages ability as APCs

- Phagocytosis - Inefficient with soluble antigens.

3 evolutionary straategies used by pathogens to evade the immune response

- Variation - Drift - Shift

2 possible routes of antigen entry into cells

- phagocytosis / endocytosis / binding to sIg - Direct entry to the cytosol

The outcome of antigen presentation in steps.

1. Antigen recognition by lymphocytes (>2 signals) 2. Cytokine synthesis 3. Lymphocyte activation 4. Clonal expansion 5. Development of effector T or B cells 6. Development of T or B cells specific for that antigen

Mechanism of cellular entry of intracellular virus/bacteria

1. Attachment 2. Entry 3. Uncoating 4. Genome replication 5. Gene expression 6. Assembly 7. Release

Mechanism of cellular entry of extracellular virus/bacteria (Endocytic pathway)

1. Entry across celllular membrane via Phagocytosis / endocytosis 2. Phagosome / endosome results 3. Phagosome / endosome in cytosol moves to golgi aparatus 4/ Phagosome / endosome processed and antigen moved to cell membrane via secretory vesicles. 5. Pathogens antigen presented on the antigen presenting cell.

Exogenous antigen processing (MHC class II pathway). Steps involved.

1. Extracellular pathogens e.g bacteria 2. Proteins processed via the endocytic pathway 3. Resultant peptides are presented by MHC class II molecules on surface of APC 4. Recognised by T cell receptor of CD4+ T helper lymphocytes 5. Cytokines are secreted 6. Enhances humoral and cellular immune responses e.g antibody or CD4+ Th1

Steps involved in the migration of immature dendritic cells during the immune response of a naive animal.

1. Immature dendritic cells reside in peripheral tissues 2. Dendritic cells migrate via afferent lymphatics to regional lymph nodes 3. Mature dentrici cell in the deep cortex.

Endogenous antigen processing (MHC class I pathway). Steps involved.

1. Intracellular pathogens e.g some viruses 2. Proteins are processed via the cytosol and proteasome 3. Resultant peptides are presented by MHC class I molecules on the surface of the APC 4. Recognised by T cell receptor of CD8+ T cytotoxic lymphocytes 5. Cytokines are secreted 6. Enhances cell mediated immunity e.g cytotoxic T lymphocytes.

Hapten

A small molecule that alone cannot elicit antibody production. Must be attached to a larger molecule (e.g carriers) to act as an antigenic determinant and elicit antibody synthesis.

Haemagglutinin

A substance that causes red blood cells (RBCs) to agglutinate.

In what instance may albumin act as a carrier for haptens to elicit an immune response?

Allergy to drugs.

Adjuvant

Any substance which when mixed with an antigen will enhance the immune response to that antigen.

Antigen

Anything causing an immune response, usually foreign material but may be own tissues (autoimmunity)

When extracellular pathogens are entering B cells, what method of entry do they use?

Binding to sIg and endocytosis.