72 Questions
Which type of immune response is triggered by tissue damage or pathogen invasion?
Innate Immune response
What does the physiological barrier of skin do to microbes?
Prevents their entry
Which enzyme found in tears and saliva cleaves peptidoglycans of bacterial cell walls?
Lysozyme
What is the main function of dendritic cells in the innate immune response?
Antigen presentation to T/B cells
What is the role of neutrophils in the innate immune response?
Phagocytosis of pathogens
Which of the following best describes the main focus of Theme 2 - Innate Immunity?
Explaining the non-specific arm of the immune system
What is the primary function of Toll-like receptors (TLRs) and Pattern Recognition Receptors (PRRs) in innate immunity?
Recognizing pathogen-associated molecular patterns (PAMPs)
What is a key role of cytokines and chemokines in inflammation?
Recruit immune cells to the site of infection
Which process involves engulfing and digesting pathogens or cellular debris by immune cells?
Endocytosis
What is a significant feature of the complement system activation?
Aids in opsonization and lysis of pathogens
Which stage of phagocytosis involves the binding of Pathogen Associated Molecular Patterns (PAMPs) or Damage Associated Molecular Patterns (DAMPs) to Pattern Recognition Receptors (PRRs) on phagocytes?
Recognition
Which molecule can be recognized by Dectin-1, a Pattern Recognition Receptor expressed on myeloid lineage cells?
β1-3 glucan
Scavenger receptor SR-A, found on macrophages (MFs) and some endothelial cells, is known to bind which molecule?
Modified low-density lipoprotein
What is the primary function of Mannose Receptor, another Pattern Recognition Receptor expressed on macrophages and dendritic cells?
Binds to mannose/fucose/α mannan
Which stage of phagocytosis involves the actual internalization of the recognized pathogen or particle by the phagocyte?
Ingestion
In phagocytosis, when cells bind opsonins coating the surface of particulate matter or microbes, this type of recognition is classified as:
Indirect (opsonic)
What is the main function of Psoriasin on skin and secretions?
Inhibit bacterial growth
Which antimicrobial protein is particularly effective in disrupting bacterial membranes, especially in bacteria?
Cathelicidins
Who first described the phenomenon of phagocytosis?
Ilya (Eli) Metchnikoff
Which type of cells primarily carry out phagocytosis?
Neutrophils
What is the general purpose of endocytosis in a cell?
Internalizing extracellular material
Which mechanism of endocytosis is characterized by the specific uptake of ligands or immune complexes?
Receptor-mediated endocytosis
What is the main size range of particles that are internalized and digested during phagocytosis?
>1mm
Which antimicrobial peptides aggregate to form pores in cytoplasmic membranes?
Defensins
Which surfactant protein functions by blocking bacterial surface components through binding?
SP-A
What is the role of Cathelicidins in disrupting microbial membranes?
Disrupt microbial membranes
Which receptor is responsible for binding LPS from gram-negative bacteria on monocytes?
CD14
Who identified TLR4 as the receptor for LPS and received the Nobel Prize for this discovery?
Beutler
Which intracellular receptors interact with PAMPs and DAMPs, activating the NFkB pathway and autophagy?
NOD-like receptors
Which receptors bind viral dsRNA and initiate anti-viral cytokine production?
RIG-like receptors
What is the function of opsonins in the immune response?
Mediate uptake through phagocyte receptors
What is the role of leucine-rich repeats in Toll-like receptors?
Binding to LPS from gram-positive bacteria & fungi
Which signaling pathways are activated upon ligation of cell surface Toll-like receptors?
NFkB and IRF transcription factors activation
What is the main difference between cell surface and intracellular Toll-like receptors?
Cell surface TLRs mainly detect viral DNA/RNA, while intracellular TLRs mainly detect bacteria/fungi PAMPs.
Which molecules can be recognized by AIM2-like receptors and cGAS/STING in the context of immune response?
DNA molecules from bacteria and viruses
Innate immunity is considered the 'specific' arm of the immune system.
False
Phagocytosis is a process involved in the adaptive immune response.
False
Toll-like receptors (TLRs) are involved in innate immune cell activation.
True
The complement system activation only involves one main cell type.
False
Cell-mediated innate immunity primarily involves chemical mediators rather than cells.
False
The first line of defense, known as FAST, is triggered by tissue damage from trauma or infection.
True
Innate immunity comprises three main types of defensive barriers: Anatomical, Physiological/chemical, and Inflammatory.
False
Skin's acidic environment with a pH range of 3-5 promotes the growth of microbes.
False
Lysozyme is an enzyme found in tears and saliva that cleaves peptidoglycans of bacterial cell walls, particularly gram-negative bacteria.
False
Neutrophils are categorized as antigen-presenting cells in the innate immune system.
False
Natural killer cells are part of the adaptive immune response rather than the innate immune response.
False
Pattern Recognition Receptors (PRRs) on phagocytes only bind to Pathogen Associated Molecular Patterns (PAMPs) and not to Damage Associated Molecular Patterns (DAMPs).
False
Scavenger receptor SR-A is only found on dendritic cells, not on macrophages.
False
Dectin-1 binds to β1-4 glucan found on fungi and bacteria.
False
The Mannose Receptor has 10 extracellular domains.
False
Phosphatidylserine is a Damage Associated Molecular Pattern (DAMP) found on the surface of damaged cells and apoptotic cells.
True
Indirect recognition in phagocytosis involves cells binding directly to the pathogen/particle.
False
Psoriasin disrupts microbial cell membranes by binding to them.
False
SP-A and SP-D are examples of defensins.
False
Cathelicidins are mainly found on skin and secretions.
False
Endocytosis is the general purpose of a cell externalizing material that is present on the inside of the cell (intracellular).
False
Pinocytosis involves specific uptake of ligands, growth factors, or hormones via receptors.
False
Phagocytosis is carried out by B cells and mast cells to internalize, kill, or digest particulate matter.
False
Receptor-mediated endocytosis involves invagination of the plasma membrane to form 'clathrin coated pits'.
True
Macro-pinocytosis is a mechanism where cells take in large 'gulps' of extracellular material.
True
Phagocytes are involved in 'cell drinking' through pinocytosis to bring in nutrients.
False
'Cell surface receptors cluster and associate clathrin around 'pits' in endosomes during pinocytosis.'
False
SR-B can only bind oxidised LDL and vimentin on the surface of apoptotic cells.
False
CD14 has a signaling domain in its cytoplasmic tail.
False
Toll gene was identified in Drosophila by Beutler in 1996.
False
TLR5/5 recognizes CPG DNA from gram-positive bacteria and fungi.
False
TLR9 detects single-stranded DNA and double-stranded RNA.
False
B cells, T cells, and granulocytes express all Toll-like receptors.
False
NOD-like receptors interact with extracellular PAMPs and DAMPs.
False
RIG-like receptors bind DNA molecules from bacteria and viruses.
False
Opsonins like IgG enhance cell attachment by cleaving pathogen cell walls.
False
Toll-like receptors can only exist as homodimers, not heterodimers.
False
Study Notes
- Innate immunity is the non-specific first line of defense against damage and infections, ready from birth.
- It includes anatomical, physiological/chemical, phagocytic/endocytic, and inflammatory features.
Anatomical Features:
- Skin acts as a mechanical barrier and has an acidic environment and commensal microflora.
- Mucosal surfaces, such as the respiratory, digestive, and urinary tracts, have cilia, mucus, and secretions that hinder bacterial attachment and provide competition.
- Epithelial cells have tight junctions that limit entry.
Physiological/Chemical Features:
- The body maintains a core temperature of 37°C (98.6°F), which inhibits microbial growth.
- Chemical mediators and antimicrobial proteins/peptides (AMPs) are produced.
- Examples include lysozyme, lactoferrin, psoriasin, surfactant proteins, defensins, cathelicidins, histatin, dermicidin, and complement components.
Phagocytic/Endocytic Features:
- Phagocytosis is the process of cells internalizing and digesting foreign particles or pathogens.
- Receptor-mediated endocytosis specifically binds ligands, growth factors, hormones, or immune complexes to receptors.
- Phagocytic cells include neutrophils, monocytes/macrophages, dendritic cells, and eosinophils.
Inflammatory Features:
- Tissue damage or pathogen invasion triggers a response involving T/B effector cells and immune cells.
- Phagocytes release inflammatory mediators, such as cytokines and chemokines, to recruit other cells and initiate tissue repair.
- The complement system is activated, leading to the formation of the membrane attack complex (MAC) and opsonization.
- Pattern recognition receptors (PRRs), including toll-like receptors (TLRs) and other PRRs, recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) to initiate an immune response.
Innate Immunity Defensive Barriers:
- Anatomical: Skin, mucosal surfaces, epithelial cells.
- Physiological/chemical: Temperature, chemical mediators, AMPs.
- Phagocytic/endocytic: Pinocytosis, receptor-mediated endocytosis, phagocytosis.
- Inflammatory: Cytokines, chemokines, complement system, PRRs.
Phagocytosis Mechanisms:
- Invagination of the plasma membrane to internalize extracellular material.
- Pinocytosis: Cell drinking to bring in nutrients and aid cellular osmoregulation.
- Macro-pinocytosis: Larger "gulps" that may play a role in membrane recycling.
- Receptor-mediated endocytosis: Specific uptake of ligands via receptor clustering and association with clathrin-coated pits.
Innate Immunity Cells:
- Phagocytes: Monocytes/macrophages, neutrophils, dendritic cells, and eosinophils.
- TLRs and other PRRs: C type lectin receptors, scavenger receptors, NLRs, RIG-like receptors, ALRs, and cGAS/STING.
Phagocytosis Stages:
- (1) Recognition: Direct (non-opsonic) or indirect (opsonic) binding of pathogens or particles to PRRs.
- (2) Ingestion: Cell surface receptors and cytoskeletal rearrangement lead to phagosome formation.
- (3) Digestion: Lysosomal enzymes degrade the engulfed material.
- (4) Exocytosis: The resulting vesicle, now called a lysosome, fuses with the plasma membrane to release its contents.
PRRs:
- Pattern recognition: Direct binding of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs).
- Examples: LPS, Flagellin, glycoproteins, mannose/fucose/α mannan, β1-3 glucan, mannans, and phosphatidylserine.
- C type lectin receptors: Mannose Receptor, Dectin-1, and DC-SIGN.
- Scavenger receptors: SR-A and SR-B.
TLRs:
- Membrane-bound receptors that activate complex signaling pathways upon ligand binding.
- Toll gene discovered in Drosophila in 1996, TLR4 identified as LPS receptor in 1998.
- Function: Induce inflammatory responses and activate adaptive immunity.
- Examples: TLR1, TLR2, TLR3, TLR4, TLR5, TLR7, TLR8, TLR9, TLR11.
Intracellular TLRs:
- Detect viral DNA and RNA, inducing type I interferons.
- Examples: TLR3, TLR7, TLR8, TLR9.
Cell Surface TLRs:
- Expressed mostly by immune cells (MCs, MFs, DCs).
- Bind bacterial and fungal LPS and flagellin.
- Activate complex signaling pathways leading to inflammation.
NLRs, RIG-like receptors, ALRs, and cGAS/STING:
- Bind intracellular PAMPs and DAMPs.
- Activate the NF-κB pathway and autophagy.
- Induce production of cytokines and inflammatory responses.
Test your knowledge on antimicrobial peptides and proteins such as Psoriasin, Surfactant Proteins, and Defensins. Learn about their functions, mechanisms of action, and specificity against different pathogens.
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