Lecture 2 innate immunity Flashcards
What are the two phagoctyes?
Macrophages and neutrophils. Both recognize, ingest and destroy many pathogens.
Where are macrophages?
Reside in the tissues, esp connective tissue, submucosal layer of the intestinal tract also in the brain.
What are neutrophils?
Short lived cells abundant in blood not present in normal healthy tissue which is different to macrophages.
Which are the first cells to encounter pathogens?
Macrophages but they are rapidly reinforced by large numbers of neutrophils. These are the first cells to cross the blood vessel wall and enter inflammatory sites.
What receptors do neutrophils use?
The macrophage mannose receptor, scavenger receptors which bind negatively charged ligands e.g., lipoteichoic acids and CD14. Ligation of these leads to phagocytosis after which the cells die.
What is inflammation defined by?
Pain-Exit of fluid and plasma proteins from blood and accumulation in tissue.
Increased redness, swelling and heat from increased blood flow.
What is inflammation initiated by?
Rapid production of cytokines and chemokines by macrophages in response to pathogens. Rapidly enforced neutrophils-first cell attracted from blood and followed by monocytes, eosinophils and lymphocytes. Induces clotting further downstream to contain infection and prevent spread of pathogens through the blood. Initiated process of tissue repair.
What are inflammation mediators?
Secreted by macrophages and other cell types in response to pathogens or in allergic reactions. Examples Lipids such as prostaglandins, leukotrienes and platelet activating factor then proteins such as cytokines and chemokine.
What do inflammatory mediators do?
Promote the recruitment of phagocytes and production of opsonising molecules. Bind to pathogens facilitating recognition of this pathogen by receptors of the immune system. For easier recognition by immune system.
What happens when wounding occurs?
Two other protective pro-enzyme cascades are triggered:
The kinin system- plasma pro-enzyme cascade that triggers the release of inflammatory mediators e.g., bradykinin-causes influx of plasma proteins and pain to immobilize the affected area and contain the infection.
The coagulation system-leads to formation of fibrin clot.
What is an example of a response to a wound?
Infectious organism entering through a wound in the skin. The organism must adhere and cross the epithelium to establish an infection. A local inflammatory/immune response may prevent this. If not it helps to contain the infection and delivers the infectious agent to local lymph nodes.
How do neutrophils and macrophages recognise they are dealing with a pathogen?
By pattern recognition receptors. E.g., mannose-binding lectin. Toll-like receptors. Both of these are present on and within phagocytes either in the cytoplasm or membrane and signal the presence of pathogens.
What are toll-like receptors?
Essential to innate immunity. First described in Drasophila embryos as recognising a protein called Spaetzle and this triggers formation of a dorso-ventral axis called the Toll pathway. 10 receptors in mice and humans. Each recognise a distinct set of molecular patterns through which most pathogens are recognised. Activation leads to production of cytokines, chemokines and cell surface receptors (e.g., B7.1, B7.2 that can stimulate T cells).
What does TLR 4 do?
Signals presence of LPS a cell wall component of gram negative bacteria e.g., Salmonella.
What does TLR-1, TLR-2 and TLR-6 recognise?
Peptidoglycan, lipoproteins, lipoarabinommannan, zymosan (yeast).
What does TLR-3 recognise?
dsRNA.
What does TLR-5 recognise?
Flagellin.
What does TLR-9 recognise?
Unmethylated CpG DNA
How do LPS signals bind to TLR4?
Do not interact directly. But bind to the acute phase protein formed in the liver in response to an infection (come to this later). Released into the serum and bind to LPS. This complex is then recognised by a receptor on the surface of the phagocyte (the CD14) this takes up the LPS complex which can bind to LBP. The complex of LPS, the binding protein and CD14. This activates a TF called NFkB in a phosphorylation reaction. Releases a promoter. Binds to gene promoters. cytokine and chemokines. Produced and released by macrophage.
How does extravasation begin?
Cytokines produced by macrophages cause dilation of local small blood vessels. Leukocytes move to periphery of blood vessels as a result of increases expression of adhesion molecules. The cytokine induced changes lead to neutrophils and monocytes (macrophage precursors). They can leave to infection site (extravasation).
What happens after extravasation has occurred?
Leukocytes migrate to the site of injury by chemotaxis. Movement along a chemical concentration gradient. Together these changes cause the characteristic signs of inflammation (redness, swelling, pain). Blood clotting occurs in the microvessels.
How does extravasation of monocytes occur?
Microorganisms in the tissue are recognised by the macrophages that reside there. Macrophages mature continuously from monocytes that leave the circulation and migrate into tissues throughout the body. They recognise and bind to blood vessel walls due to the adhesion molecules on the vascular endothelium. Endothelium bound chemokines signal to the monocyte to migrate.
What are the steps of phagocytosis?
Recognition and attachment of the particle to be ingested (the macrophage expresses receptors for many bacterial constituents). Bacteria binding to macrophage receptors initiate the release of cytokines and small lipid mediators of inflammation. Engulfment with formation of phagocytic vacuole. Killing or degradation of the ingested material.
What toxic molecules do macrophages and neutrophils produce to kill the micro organism?
NO, O2-(superoxide) and H2O2. Superoxide is generated by NADPH oxidase=the respiratory burst as it is accompanied by a transient increase in oxygen consumption and production of H2O2. Further chemical and enzymatic reactions produce hydroxyl radicals, hypochlorite and hypobromite ions. Killed microorganisms are then degraded by lysosomal hydrolases.
