Lecture 11: 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

What is phagocytosis promoted by?

Answer 2

• 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 3

What three molecules trigger ‘danger signals’ in innate immune recognition?

Answer 3

• PAMPs
• Bacterial metabolic products
• Heat shock proteins

Question 4

What are the actions of acute phase proteins?

Answer 4

• Enhance host resistance
• Minimise tissue injury
• Promote resolution and repair of inflammatory lesions

Question 5

What are the 3 outcomes of the complement cascade?

Answer 5

• Opsonisation
• Chemotaxis
• Increased vascular permeability

Question 6

Lymphocyte: Effectors and regulators

Answer 6

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 7

Describe the exogenous pathway of antigen processing

Answer 7

• Antigens ingested into vesicles
• Antigens broken down into peptide fragments by acidification and protease degradation
• Vesicles containing fragments fuse with those containing class II MHC
• Peptide presented on cell surface

Question 8

Describe the endogenous pathway of antigen processing

Answer 8

• Abnormal proteins produced by cell due to changes in gene expression
• Peptide fragments broken down by proteosomes
• Peptides transported into lumen of ER by TAP
• Peptide binds to class I MHC
• Class I MHC released from TAP-1

Question 9

APC functions

Answer 9

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