Immuno: Immune response to infection Pt.1 Flashcards
What are the two main routes of infections of pathogens?
- External epithelia (e.g. skin)
- Mucosal surfaces (e.g. GI tract)
List some features of skin that makes it an effective barrier to infection.
- Consists of tightly-packed keratinised cells
- Low pH
- Low oxygen tension
- Sebaceous glands
What do sebaceous glands produce that has antibacterial effects?
- Hydrophobic oils - repels water and microorganisms
- Lysozyme - destroys the structural integrity of the bacterial cell wall
- Ammonia and defensins - anti-bacterial properties
Describe the defensive features of mucosal surfaces.
- Traps invading pathogens
- Cilia promote the removal of mucus
- Contains secretory IgA which binds to pathogens and prevents them from attaching to and penetrating epithelial cells
- Contains lysozyme and other antimicrobial peptides
- Lactoferrin starves invading bacteria of oxygen
How do commensal bacteria act as a barrier to infection?
Competes with pathogenic bacteria and produces various antimicrobial agents
List the cells of the innate immune system.
- Polymorphonuclear cells
- Monocytes/macrophages
- NK cells
- Dendritic cells
List the soluble components of the innate immune system.
- Complement
- Acute phase proteins
- Cytokines and chemokines
List some key features of cells of the innate immune system.
- Identical responses in all individuals
- Cells express genetically-encoded receptors (PRRs) that allow them to detect pathogens at the site of infection
- Cells have phagocytic capacity
- Cells secrete mediators (e.g. cytokines/chemokines) that regulate the immune response
Name the resident macrophage in the following tissues/organs:
- Liver
- Kidney
- Bone
- Spleen
- Neural tissue
- Connective tissue
- Skin
- Liver = Kupffer cells
- Kidney = Mesangial cells
- Bone = Osteoclasts
- Spleen = Sinusoidal lining cells
- Neural tissue = Microglia
- Connective tissue = Histiocytes
- Skin = Langerhans cells
How do macrophages differ from polymorphonuclear cells?
They can process antigens and present them to T cells
Outline the process of phagocyte recruitment in response to infection.
- Cellular damage and bacterial products trigger the production of inflammatory mediators (cytokines and chemokines)
- Cytokines enhance vascular permeability
- Chemokines attract phagocytes (chem = chemistry = attract)
Describe how cells of the innate immune system recognise pathogens.
- Neutrophils mobilised very quickly from BM and migrate to site of infection
- Pattern-recognition receptors (PRRs) recognise generic motifs called PAMPs (e.g. bacterial sugars, DNA and RNA)
- Fc receptors on these cells allow binding to the Fc portion of immunoglobulins thereby allowing phagocytosis of immune complexes
What are examples of PRRs?
- Toll-Like Receptors (TLRs)
- Mannose Receptors
What is opsonisation?
The molecular mechanism that uses opsonins to make a molecule (e.g. antigen) more palatable to the phagocyte.
I.e. opsonins act as a bridge between the pathogen and the phagocyte receptors
Which other factors can bind to phagocytes to facilitate phagocytosis?
- Complement components (e.g. by binding to CR1)
- Acute phase proteins (e.g. CRP)
- Antibodies
How do NK cells determine whether to lyse cells or not?
- They have inhibitory receptors which recognise self HLA and they have activating receptors that recognise heparan sulphate proteoglycans
- The balance of these signals determines the response
- I.e. if HLA downregulated, activatory signal will become dominant
- They kill ‘altered self’ cells (e.g. malignancy or virus-infected cells)
