Innate immunity and antigen presentation

Question 1

Brief definition innate immunity

Answer 1

Physical barrier to infectious agents, such as microbicidal factors in body fluids (lysozyme, complement) and phagocytic cells.
Involve acute phase proteins

Question 2

Phagocytosis summary

Answer 2

Adherence, membrane activation, phagosome formation, fusion and digestion and release of degraded products

Question 3

What is phagocytosis promoted by?

Answer 3

• PAMPS: Pathogen associated molecuar patterns, receptors for common bacterial cell wall components. weak interactions.
• Receptors for C3b complement component (complement mediated opsonisation)
• Receptors for Fc region of antibodies (immune complex mediated opsonisation)

Question 4

What are the three types of PAMPS

They act as ligands that neutrophils recognise, and also that cells like dendritic cells recognise and release danger signals to immune system

Answer 4

Common cell wall structures: Lipopolysaccharides, peptidoglycans (mannans, mannoproteins

Bacterial metabolic products: N-formylmethioine peptides

Heat shock proteins: released by stressed cells

Question 5

Acute phase proteins: Release, action

Answer 5

Release: Plasma proteins produced due to a danger signal from a dendritic cell for example IL-1. produced in the liver.

Act to promote tissue repair and resolution and limit damage. Enhance host resistance

Question 6

Complement generalised?

Answer 6

First complement components bind to common cell wall components.’
Set off enzymatic set of reactions, activating furhter complement components that: Increase vascular permeability, chemotaxis of neutrophils and opsonisation (C3b)

Question 7

Primary and secondary lymphoid organs

Answer 7

Primary: Bone marrow and Thymus (T cells originate in bone marrow and mature in thymus)
Secondary: Lymph nodes (tissue), spleen (blood), accessory lymphoid tissue (mucosal surfaces)

Question 8

Cells of adaptive immune system
Lymphocyte: Effectors and regulators

Effectors: ____ production ( B cells); ____ ____ _____ (CD8 T lymphocytes); NK cells; ____ ____- ____ _____, ADCC, K cells.
Last two functions of same subset of cells

Regulators: ____ production (CD4 Tcells): ____ (viruses, bacteria, intracellular agents); ____ (parasites, allergies, multicellular); ____( regulatory T cells, down regulation); ____ (mucosa and inflammation)

Answer 8

Effectors: Antibody production ( B cells); antigen specific cytotoxicity (CD8 T lymphocytes); NK cells; antibody dependent cellular cytotoxicity, ADCC, K cells.
Last two functions of same subset of cells

Regulators: Cytokine production (CD4 Tcells): TH1 (viruses, bacteria, intracellular agents); TH2 (parasites, allergies, multicellular); Treg( regulatory T cells, down regulation); TH17 (mucosa and inflammation)

Question 9

Antigen transport and presentation

• Multiplying ____ in infection site e.g ___. _____ cells uptake ____, release ____ _____ also. Are ____
• Transport through the _____ to _____ nodes, and rest in _____ region
• Present _____ to _____ that travel through/into the ____
• _____ specific cells are recruited

Answer 9

• Multiplying bacteria in infection site e.g skin. Langerhans cells uptake antigens, release danger signals also. Are APC’s
• Transport through the lymphatics to lymph nodes, and rest in paracortical region
• Present antigens to lymphocytes that travel through/into the node
• Antigen specific cells are recruited

Question 10

APC functions

Answer 10

Antigen collection and transport
Antigen concentration
Antigen processing
Antigen presentation to lymphocytes
Co-stimulation of lymphocytes: by surface molecules or pro-inflammatory cytokines
Tolerance induction

Question 11

Exogenous pathway of antigen presentation

Answer 11

Dendritic cells

Antigenic material is phagocytosed (fused with protease), and combined with a Class II MHC such as HLA DP, DQ or DR. Then expressed on the cell surface membrane

Question 12

Endogenous pathway of antigen presentation

Answer 12

Inside any nucleated cell of our body

Viral infection, or altered gene expression by tumour cell?
New proteins made and broken down by proteosomes.
Some breakdown products on Class I MHC HLA A, B and C through TAP complex then MHC I to surface

Question 13

Exogenous pathway versus Endogenous

Answer 13

Exogenous: peptides derived form ingested material; only specialised APC’s (dendritic,, B cells), presented by MHC II.

Endogenous: Peptides derived from cytoplasmic proteins, normal metabolism( viral peptides, modified self peptides (tumours), presented by MHC I