Introductory Immunology Flashcards
How are microbes recognised by the immune system?
Components of innate immunity recognise structures that are shared by various classes of microbes and are not present on host cel
Receptors of innate immune system are encoded in the germline and not subject to recombination - identical receptors on all cells of same lineage
Innate immunes system responds in same way to repeat encounters with microbe
Adaptive immune system responds more efficiently to each successive encounter with a microbe
What are the components of the innate Immunity? (5)
Epithelial barriers - skin, g.i tract, respiratory tract Phagocytes Complement Soluble factors Cytokines
Name and describe the phagocytes
Neutrophils and monocytes - blood cells that are recruited to sites of infection where they recognise and ingest microbes
neutrophils - most abundant
- first cell type to respond to most infections
- cannot survive long periods in extravascular tissues
Monocytes - can survive long periods in extravascular tissues where they become macrophages
Dendritic - perform a key role in linking the innate and adaptive immune response
How do phagocytes respond to an infection in extravascular tissue?
Migrate to extravascular tissue infection by binding to endothelial adhesion molecules and are attracted to the site by chemo-attractants
If an infectious agent breaches the epithelia the resident macrophage recognises it and produces cytokines
- tumour necrosis factor (TNF) and interleukin-1 (IL1)
TNF and IL-1 stimulate endothelial cells to express adhesion molecules; E-selectin and P-selectin
What are the four stages of leukocyte movement from circulatory system to site of infection?
1 - rolling
2- integrin activation
3 - tight stable adhesion
4 - migration rough endothelium
What are the receptors on phagocytes?
Toll like receptors (TLRs)
- specific for different components of microbes
- TLR-2 is essential for macrophage responses to several bacterial lipoglycans
- TLR-4 binds lipopolysaccharide (LPS)
- TLR-5 binds flagellin
- TLR binding activates a transcription factor NF-kB, which stimulates production of cytokines and enzymes
N-formylmethionine-containing peptide
- promotes increase integrin avidity and cytoskeletal changes
Describe phagocytosis
Phagocytes internalise microbe into a compartment known as the phagosome
Phagosome fuses with lysosome - phagolysosome
Microbe is bound to receptors that deliver signals that activate enzymes
- phagocyte oxidase
- inducible nitric oxide synthase
- lysosomal proteases
What are natural killer cells?
Lymphocytes that respond to intracellular pathogens
Produce macrophage-activating interferon gamma
Make up 10% of lymphocytes
Cytoplasmic granules and characteristic surface markers
NK cell recognise host cells that are altered by invading pathogens
What is the complement system?
Collection of circulating and cell membrane proteins
Role in host defence against microbes (bacteria in particular)
Complement = assists in antimicrobial activity of antibodies
Bacteria can activate complement without antibody interaction
What is the acute phase response?
Proteins that circulate in the plasma involved in defence against infections
MBL (mannose-binding lectin)
- recognises microbial carbohydrates
- coats the microbe and facilitates complete and phagocytosis
Surfactant protein - protects the lungs
CRP (C-reactive protein) - binds phosphorylcholine on microbes
What are cytokines?
Mediate cellular reactions of immunity
Soluble proteins
Interleukins: produced by leukocytes to act on leukocytes
Innate immunity- principal source of cytokines are macrophages
Adaptive immunity - principal source of cytokines are Th cells
What is an antibody?
Molecule composed of four polypeptide chains
Two identical light chains
Two identical heavy chains - determine isotype of antibody and effector function
Each contain one variable region and one constant region
What is the difference between innate and adaptive immunity?
Innate
- not improved by repeated infection
- uses lysozymes, antimicrobial peptides and acute phase proteins to fight infections
- consists of phagocytes and natural killer cells
- quick response
Adaptive
- improved by repeated infection
- uses antibodies and cytokines to fight infection
- consists of lymphocytes
- slower response
