Innate immunity

what is involved in humoural immunity?

soluble proteins

what is it called when there are cells induced for an immune response?

cell mediated immunity

what is the first line of defence?

epithelial cells and mucus membranes

describe what happens during alternative complement activation

o   Occurs in the presence of an invading pathogen (bacterial pathogen)

o   C3 produced by the liver is constantly circulating in blood and lymphatic system in low concentrations

o   It hydrolyses into two subunits C3b and C3a

o   In the presence of bacterium, C3b will bind to the bacterial cell surface (polysaccharide in cell wall)

o   This is then sufficient to start the alternative complement cascade

o   C3b becomes stabilised on the bacterial surface by Factor D and picaridin

o   Factor B binds to C3b to form C3 convertase

o   C3 convertase then converts as much C3 as it encounters into C3a and C3b

o   This C3b covers as much of the bacterial surface as it can (the bacterial cell is being opsonised)

describe what happens during the cell mediated resposne

o   Neutrophils (polymorphs) and monocytes have receptors on their surface for C3b

o   Neutrophils and monocytes are phagocytic so recognise the bacteria that is opsonised so can destroy it

o   Neutrophils and monocytes are also always circulating, waiting for C3b

§  Monocytes are short lived as they differentiate a lot and these turn into macrophages

§  These are localised at strategic points in the body, where they may come across a bacterial cell or pathogen

how does phagocytosis occur?

o   There is attachment of the macrophage to bacterial cell engulfed by C3b via pattern recognition receptors

o   Pseudopodia forms a phagosome

o   The granule fuses and kills the bacterial cell by releasing lysozymes

o   The microbial products are then released and what happens with these depends on the cell type

what is c3a?

o   C3a is a chemoattractant and is used by the neutrophils to be attracted to the site of infection

what occurs in the immune response after phagocytosis?

-              Neutrophils are attracted to sites of infection by C3a and release vacuole contents after phagocytosis

o   C3a is a chemoattractant and is used by the neutrophils to be attracted to the site of infection

o   The chemoattractant form a concentration gradient which the neutrophils follow

o   Neutrophils are active moving cells so can pass through blood vessels and such

o   The release of C3a also stimulates the liver to produce more C3 (amplification of the innate immune response)

This increases opsonisation

what happens during an acute inflammatory response?

-              Polymorphs pass up the concentration gradient through C3a to the site of infection

-              Neutrophils then bind to C3b engulfing a bacterial cell

-              Mast cell degranulation – part of the inflammatory response

o   Granules inside degranulate to release their mediators

o   Mediators include platelet activating factors, histamines etc

o   These mediators follow the C3 gradient by chemotaxis and move to the site of infection

o   Increases volume of blood and changing elasticity of blood vessels, allowing more polymorphs to pass through

o   Increases flow of C3

o   Mast cell degranulation caused by C3a

why is there inflammation during infection?

increased blood flow to the site of infection

what is different about a gram negative infection?

-              more soluble proteins are recruited as part of the immune response so, the complement pathway keeps on going

-              C3 is not degraded by the enzyme and is recruited on to the enzyme called C5 convertase

-              C5 convertase breaks down C5 into C5a and C5b

-              C5B binds to cell membrane and attracts more proteins part of the complement pathway

-              Also forms a pore (membrane attack complex) in the lipopolysaccharide layer

what can and can’t viruses be eliminated by?

-              Viruses can be eliminated by humoral response BUT NOT COMPLEMENT

what type of pathogen is the complement pathway limited to?

bacteria and some fungi

what is MHC class I?

o   protein that allows cells to be recognised as self

o   So, all healthy cells have this

what can viruses do to MHC class I?

-              Virally infected cells can withdraw the MHC class I molecule from the surface of the host, so cell is no longer recognised as self, so is destroyed

-              The cell can then release cytokines (specifically interferons) to signal that there is a viral infection

-              Natural killer cells will recognise the infected cell as non-self

o   These are filled with granules, which destroy the infected cells