Introduction to Immune Response

Cytokines functions

Mature dendritic cells

↑ Macrophage function

↑ selectin

↑ vascular permeability

↑ function of other immune cells (survival, proliferation, cytotoxicity)

Role of selectins

Receptors on endothelial cells that bind to ligands on neutrophils causing them to decelerate on the blood vessel wall

Give 2 examples of cytokines

interleukins (IL-1)

TNF

Chemokines functions

Attract other immune cells

Chemokine example

IL8

How do chemokines attract inflammatory cells into tissues

By increasing their motility

Pluripotent haematopoietic stem cells can go down what 2 lineages to become what types of cells

What’s the most abundant white blood cell

Neutrophils - comprising well over 50% of WBC’s

Name the 3 main cells of the myeloid lineage

Neutrophils

Macrophages

Dendritic cells

Neutrophils role

phagocytosing and killing microbes

secrete cytokines & chemokines

(make pus)

Process of neutrophil extravasation

Neutrophils develop from where

Bone marrow

Role of integrins

Strong adhesion molecules on neutrophils that facilitate their active migration into tissues

Macrophages are activated by what

PRRs (pathogen recognition receptors) (toll-like receptors) on cell surface

Endosomes (in other cell compartments) that recognise PAMPs (Pathogen Associated Molecular Patterns) & DAMPs (Danger Associated Molecular Patterns)

Give 3 examples of PAMPs/DAMPs

Examples include certain sugars not seen in humans e.g. lipopolysaccharide (LPS/endotoxin), nucleic acids (DNA/RNA), factors released factors by dying cells

Macrophages develop from where

Bone marrow

Macrophage general response to activation

The danger signal activates the macrophage promoting phagocytosis of microorganisms & abnormal cells

The macrophage begins to secrete cytokines and chemokines.

Presents antigens to T cells

4 specific things released by macrophages

Role of TNF

Role of IL-6

Role of IL-8

Role of IL-12

In the complement system associated with macrophages, what is the role of C3a & C5a

Induce inflammation & chemotaxis

What happens when C3a & C5a activate mast cells

Degranulation → mast cells release histamines & other vasoactive amines → enhances vascular permeability

Role of dendritic cells

Present antigens to T cells

Dendritic cells develop from where

Bone marrow

Name the 3 main cells of the lymphoid lineage.

Which are involved in innate / adaptive immunity?

NK cells (innate)

T cells (adaptive)

B cells (adaptive)

How do NK responses generally differ from T & B cell responses 

T & B cells make specific receptors to recognise antigens because they are adaptive - NK cells don’t

How do T & B cells make specific receptors to recognise antigens

Genetic recombination of limited precursors & germline DNA

What type of receptors do NK cells use (where do they come from)

They are germline encoded - not rearranged 

So they don’t recognise specific receptors

What activates NK cells

1. Missing self: MHC doesn’t reach KIR (cells that lack MHC class 1 molecules)

2. Stress induced: Have high stress induced molecules - abnormal proteins

3. ADCC: Antibody-dependent → antibodies recognised by Fc receptors

What is KIR

Strong inhibitory receptors on NK cells that inhibit NK when they recognise MHC

Source of antibodies on cells recognised by Fc receptors

B cells

NK response to activation

Kill with cytotoxic granules containing lytic proteases - perforin & granzyme

Kill with death ligands - TRAIL & Fas

Release cytokines

How do NK cells, macrophages and dendritic cells influence each other

Macrophages produce cytokines → activate NK cells → release cytokines → mature dendritic cells → enhance macrophage function

Where do T cells come from

Bone marrow precursors → Thymus → T Cells

What activates T cells (generally)

TCRs (T cell receptors) recognise a combination of antigen‐derived peptides and MHC

What specific antigens do CD4 and CD8 T cells recognise

(give 3 examples of each)

CD4 T cells → MHC class II antigens (HLA-DR, DD, DQ)

CD8 T cells → MHC class I antigens (HLA-A, B, C)

Function of CD4 and CD8 T cells

CD4 → Help other immune cells & limit unwanted immune response

CD8 → Kill infected cells

Explain the 1st of the 3 signals necessary to fully activate T cells

Signal 1: TCRs bind to antigens → CD4/8 activates ITAMs on CD3z → CD3 activates T cells

Explain the 2nd of the 3 signals necessary to fully activate T cells

Signal adhesion molecules (LFA-1 [on T cell] & ICAM-1 [on APC/tumour cell]) → cause tight binding of APC & T cell → Co-stimulatory molecules (on the APC) bind to CD28 (on T cell) → Prevents apoptosis of T cell & provides 2nd signal → T cell activated

Explain the 3rd of the 3 signals necessary to fully activate T cells

Cytokines released → Clonal expansion & proliferation → T cell activated

What allows T cells to stay active for a long time

Adhesion molecules (LFA1 & ICAM1) form an immune synapse

Why must T cell activation be controlled

Can lead to autoimmune disease

What 3 different T cells have what 3 different responses to activation

Helper T → Activates B cells & helps other immune cells

Regulatory T → Limits excessive/unwanted immune response

Cytotoxic T → Kill infected cells

How are T cells deactivated

“Off switch” molecules: PD1 on T cells binds to PDL1 on APCs → Phosphates dephosphorylate signalling molecules → inhibit kinase activating signals → turn off T cells

Competitive inhibition: CTLA4 competes with CD28 (both on T cells) to bind to CD80/CD86 on APCs → Limits prevention of apoptosis

Tregs: Tregs express ligands for immune checkpoints (PDL1/CTLA4) → release suppressive cytokines & eliminate CD4 & CD8

What problem can occur with Tregs 

They can be overactive in cancer

Where do B cells develop

Bone marrow

How are B cells activated

Helper T cells

or

Follicular dendritic cells present antigens

What 2 cells can B cells differentiate into when activated - what role does each one carry out

Memory B cells - wait to mount rapid response if antigen presents again

Proliferation into plasma cell that makes antibodies → Binds to antigen → Neutralise APC / Mark for destruction by NK cells / macrophages

What decides what role B cells go into

CD4 T cells

CD40L → Memory B

CD40 → Plasma cell

Name the 2 regions of an antibody & their function

Fab region → Antigen binding (variable)

Fc region → links complement & effector cells (NK cells → ADCC / Macrophages → ADPC)

How are TCRs similar to Fabs

Both have 2 different peptide chains

Both have variable, constant & hinge regions

How do TCRs differ from Fabs

TCR = membrane bound with 1 antigen binding site

Fab = not membrane bound. Has 2 binding sites

Do both B and T cells exhibit immunological memory

Yes

What immune cells are involved in humoral immunity

B cells

(Humoral immunity = the part of the adaptive immune system that uses B cells and antibodies to fight pathogens in body fluids)

What type of molecules can antibodies be

Antigens can be proteins, carbohydrates, lipids, nucleic acids, small molecules released in a soluble (secreted) version

Via what mechanism do B cells have the ability to make millions of antibody molecules capable of recognizing numerous antigens

Via somatic recombination B cells have the ability to make millions of antibody molecules capable of recognizing numerous antigens

Yellow = Region

Purple = Heavy/Light Chain

Green = Other

The BCR (B Cell Receptor) is a complex containing an antibody on the surface of the B cells, which is linked to signalling molecules, e.g. ….

tyrosine kinases

Strength of B cell activation depends on what

how good a fit the BCR is for the antigen

How is the BCR used in B cell cancer treatment

Some B cell cancers are treated by using kinase inhibitors that block signalling through the BCR

Compare Primary vs Secondary Immune Response

Primary response: slower, lower antibody levels

Secondary response: rapid, strong, long-lasting

Where do Follicular Dendritic Cells present antigens to B cells

In the germinal centre of lymph nodes

How does B cell selection for antibody production work

Only B cells that receive the strongest survival signal (best antigen:antibody fit) are selected and survive.

Others undergo apoptosis (programmed cell death)

When the B cells are selected what other cell selects whether they become antibody producing Plasma cells or Memory B cells

Helper CD4 T cells provide additional survival signals helping the selected B cells to mature into either antibody producing Plasma cells or Memory B cells

Following antigen recognition what do B cells do to increase their efficiency & to make the tightest fit possible to antigen

B cells rapidly proliferate and mutate their Ig genes to make the tightest fit possible to antigen

MHC stands for what

major histocompatibility complex

What is MHC & what does it do

MHC is a genetic locus that controls histocompatibility

In early transplantation experiments, the donor and recipient were found to need the same MHC locus (tissue type) in order to avoid graft rejection. Why?

MHC molecules are recognized by T cells, via their T-cell receptors (TCRs) and unless the donor and recipient are matched for these molecules the host T cells see the donor cells as foreign and induce rejection

Alternatively, donor T cells see host cells/tissues as foreign and cause graft versus host disease.

True / False: MHC genes are highly polymorphic

True

MHC antigens in humans are aka what

HLA antigens (human leukocyte antigens)

The T‐cell receptor (TCR) complex has how many chains, called what

2 - alpha and Beta

Co‐clustering of CD4 or CD8 with the TCR complex facilitates signal propagation though what mechanism through what molecule

through phosphorylation of immunoreceptor tyrosine‐based activation motifs (ITAMs) within the CD3 ζ chain

Clinical significance of CD3 ζ (zeta)

an important component of artificial TCR’s e.g. CAR-T

In what stage of T cell activation (which signal involving which molecule) can T cell receive too much activating signal? What happens then?

In T cell activation by signal 2 (using CD28)

A strong activating signal, if not balanced by a strong anti-apoptotic signal from an anti-apoptotic protein (Bcl-xL) can induce apoptosis - activation‐induced cell death)

Name 2 Immune Checkpoint Receptors and their Ligands

Immune Checkpoint Receptors (PD-1 and CTLA4)

Ligands (e.g. PD-L1 and CD80/86)

How do immune checkpoints inhibit activating signals

Activation of immune checkpoints → phosphatases dephosphorylate signalling molecules → inhibit activating signals

Do phosphatases & kinases work together or oppose each other? Explain

Phosphatases oppose the action of kinases.

Kinases phosphorylate amino acid substrates, typically inducing cellular activation e.g. tyrosine kinases

Phosphatases inhibit activating signals

When are CTLA-4 and PD-1 upregulated on activated T cells

usually after prolonged activation

What type of T cell is often overactive in cancer

Tregs → impaired immune response