innate_immune_system_flashcards
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What are the three main components of the innate immune system?
Physical barriers, cells, and soluble mediators.
What is the function of tightly packed keratinised cells in the skin?
They physically limit colonisation by microorganisms.
What are the physiological factors of skin that contribute to innate immunity?
Low pH and low oxygen tension.
What do sebaceous glands in the skin produce and what is their function?
They produce hydrophobic oils that repel water and microorganisms.
What is the role of lysozyme in sebaceous glands?
Lysozyme destroys the structural integrity of bacterial cell walls.
What additional properties do sebaceous glands have?
Ammonia and defensins have anti-bacterial properties.
What is the function of secreted mucous on mucosal surfaces?
It acts as a physical barrier to trap invading pathogens.
What role does secretory IgA play on mucosal surfaces?
It prevents bacteria and viruses from attaching to or penetrating epithelial cells.
How does lysozyme function on mucosal surfaces?
It directly kills invading pathogens.
What is the role of lactoferrin on mucosal surfaces?
It acts to starve invading bacteria of iron.
How do cilia function in the innate immune system?
They directly trap pathogens and contribute to the removal of mucous.
What physical maneuvers assist cilia in removing pathogens?
Sneezing and coughing.
What are the most abundant cells of the innate immune system and their function?
Neutrophils; they are predominantly involved in phagocytosis and killing of microbes.
What is the role of basophils and mast cells?
They release inflammatory mediators such as histamine.
What is the importance of eosinophils?
They are important in defense against parasites.
Where are monocytes produced and what happens to them?
Produced in bone marrow, circulate in blood, and migrate to tissues where they differentiate to macrophages.
What are the primary functions of macrophages?
Phagocytosis and antigen presentation to T-cells.
What are macrophages called in the liver?
Kupffer cells.
What are macrophages called in the kidney?
Mesangial cells.
What are macrophages called in the spleen?
Sinusoidal-lining cells.
What are macrophages called in the bone?
Osteoclasts.
What are macrophages called in the lungs?
Alveolar macrophages.
What are macrophages called in the CNS?
Microglia.
What are macrophages called in connective tissue?
Histiocytes.
What are macrophages called in the skin?
Langerhans cells.
Where do dendritic cells reside and what is their function?
They reside in peripheral tissues and are important antigen presenting cells.
What do dendritic cells do after phagocytosis of microbes?
They migrate to lymph nodes and present antigens to T-cells.
Which T-cells can dendritic cells activate?
Both CD4+ and CD8+ T-cells.
What do Fc receptors on dendritic cells detect?
Immune complexes.
What is the role of cytokines expressed by dendritic cells?
They regulate the immune response.
Where are NK cells present and what is their function?
They are present within blood and may migrate to inflamed tissue.
What do inhibitory receptors on NK cells detect?
Self-HLA molecules to prevent inappropriate activation by normal self.
What do activating receptors on NK cells detect?
Natural cytotoxicity receptors that recognize heparan sulfate proteoglycans.
What is the cytotoxic function of NK cells?
They kill ‘altered self’ such as malignant or virus-infected cells which lack inhibitory signals or have activating signals.
What are the main pro-inflammatory cytokines?
TNF-α and IL-1.
What is the function of chemokines?
They act as chemo-attractants to recruit leukocytes towards the site of inflammation.
What is the role of IFN-γ?
It is released in response to intracellular pathogens (viruses) and is important in macrophage activation.
What is the role of IFN-α?
It is important in defense against viruses.
What does the complement system consist of?
Numerous, tightly regulated soluble factors that circulate in the bloodstream in their inactive form.
What happens once the complement system is activated?
It has numerous roles such as opsonisation, vasodilation, increasing permeability of blood vessels, chemo-attraction, activation of leukocytes, and direct cytotoxicity via formation of the membrane attack complex (MAC).
How can the complement cascade be activated?
Via three pathways: Classical pathway, Mannose-binding lectin (MBL) pathway, and Alternative pathway.
What triggers the classical pathway of the complement cascade?
When an antibody binds to its specific antigen, activating C1 which leads to activation of C2 and C4, then C3 convertase.
What triggers the mannose-binding lectin (MBL) pathway?
MBL binds to carbohydrates on the surface of bacteria, leading to activation of C2 and C4, then C3 convertase.
What triggers the alternative pathway of the complement cascade?
C3 directly binds to bacterial cell wall components such as LPS, leading to autoactivation of C3 convertase.
What is the major amplification step in the complement cascade?
Activation of C3.
What forms the membrane attack complex (MAC)?
The final common pathway involving C5-C9.
What is the function of the membrane attack complex (MAC)?
It punches holes in the bacteria, effectively killing them.
What triggers phagocyte recruitment?
Cellular damage and bacterial products trigger the local production of inflammatory cytokines and chemokines.
How do cytokines and chemokines aid in phagocyte recruitment?
Cytokines activate vascular endothelium enhancing its permeability, while chemokines attract phagocytes.
How do pattern recognition receptors function in recognizing microorganisms?
They recognize generic motifs known as pathogen-associated molecular patterns (PAMPs) such as bacterial sugars, DNA, and RNA.
What is the role of Fc receptors in microorganism recognition?
They allow recognition of immune complexes.
How does endocytosis occur in the innate immune system?
It is facilitated by opsonisation, where opsonins act as a bridge between the pathogen and the phagocyte receptors.
Give examples of opsonins.
Antibodies binding to Fc receptors, complement components binding to complement receptors (CR1), and acute phase proteins such as c-reactive protein (CRP).
What is a phagolysosome and its function?
A compartment formed when a phagosome fuses with a lysosome, where killing of the organism occurs.
What are the oxidative killing mechanisms used by phagocytes?
NADPH oxidase complex converts oxygen to reactive oxygen species (e.g., superoxide and hydrogen peroxide), and myeloperoxidase catalyses production of hydrochlorous acid from hydrogen peroxide and chloride.
What is the role of hydrochlorous acid in oxidative killing?
It is a highly effective oxidant and antimicrobial agent.
What are the non-oxidative killing mechanisms used by phagocytes?
Release of bactericidal enzymes such as lysozyme and lactoferrin into the phagolysosome.
What is the outcome of non-oxidative killing mechanisms?
Broad coverage against bacteria and fungi.
What happens to neutrophils after phagocytosis?
Phagocytosis depletes neutrophil glycogen reserves, followed by cell death.
What is the result of neutrophil death in infected tissue?
Residual enzymes are released causing liquefaction of closely adjacent tissue, leading to the accumulation of dead/dying neutrophils and formation of pus.
What happens in cases of extensive localized formation of pus?
Abscess formation occurs.
