Immuno 3
Explain how CRP triggers the classical complement fixation pathway with C4 and C2
CRP complexes with C1, which when bound cleaves C4 --> C4a and C4b (similar to MBL action on C4) C4b binds pathogen surface, forms the Classical C3 convertase cleaving C3 --> C3a and C3b
Name the pathogens detected by complement receptors 3 and 4
Gram negative LPS, Leishmania (lipophosphoglycan), Bortella pertussis (hemagglutinin), Candida/Histoplasma (glucans)
Name the pathogens detected by CD14
Gram negative LPS, Peptidoglycan, LTA, mannuronic acid
Describe the types of molecules bound by mannose-binding lectin
mannose-containing carbohydrates of bacteria, fungi, protozoa, and viruses; it is also an acute-phase protein.
Explain the NK-cell circulation pattern
originate and develop in bone marrow -->blood -->tissue --->lymph ---> blood
Describe how MBL forms classical C3 convertase (C4bC2a)
Activated MBL complex cleaves C4 ---> C4a (soluble anaphylatoxin) and C4b (binds pathogen surface). MBL then cleaves C2 --> C2a (binds C4b) & C2b. C4bC2a = Classical C3 Convertase - component of both lectin and classical pathways
Explain how dendritic cells initiate adaptive immunity
Activation, proliferation, and differentiation of NK cells driven by dendritic cells. Production of effector NK cells that secrete cytokines and kill virus-infected cells.cWhen NK cells are abundant and outnumber dendritic cells, they can kill the dendritic cell. NK cells suppress the dendritic cell function. When NK cells are scarce and are outnumbered by dendritic cells, they drive the dendritic cells to mature into the form that initiates adaptive immunity. The innate immune system response is failing to terminate the infection and the adaptive immune response is initiated
List what cells can make IFN & have IFN receptors.
All Cells
Explain what induces the synthesis of mannose-binding lectin (MBL)
Bacteria induced macrophages to produce IL-6 --->hepatocytes synthesize acute-phase proteins. CRP, fibrinogen, and mannose-binding lectin - acts as an opsonin and complement activator.
Name the pathogens detected by Dectin-1
Bacteria-myobacterial ligand; Fungi-B-glucans
Name 2 prominent acute-phase proteins
C-reactive protein (CRP), and serum amyloid A protein - concentrations rise hundredfold
Describe function of CRP
C-reactive protein acts as an opsonin, triggering the classical pathway of complement fixation in the absence of specific antibody. C-reactive protein also binds to the surface of phagocytes, suggesting that it can deliver pathogens to these cells for elimination.
Describe the role of classical C3 convertase
Classical C3 Convertase cleaves C3 ---> C3a and C3b which opsonizes the pathogen surface
Explain the role of integrins in the immune system
Contribute to adhesive interactions between cells. Such interactions enable cells of the immune system to communicate with each other and with other types of cell.
Explain what initiates the type I interferon response
Cytoplasmic sensor proteins (RIG-1-like receptors / RLRs) detect viral nucleic acids and initiate a defensive response - secretion of type I interferons and NFκB à inflammatory cytokine release
Describe the function of NOD-like receptors
Detect products derived from intracellular degradation of phagocytosed pathogens from the phagolysosome. Recognize components of bacterial cell walls
TLR
Extracellular domain recognizes pathogens, cytoplasmic domain conveys this information to the inside of the cell. Leucine-rich repeat region (LRR) - pathogen recognition domain with 20-30 repeated AAs rich in hydrophobic leucine
Explain how IL-12 results in further macrophage activation via NK cells
IL-12 induces NK cells to proliferate and secrete cytokines that sustain macrophage activation.
Describe the positive cytokine feedback loop involving NK cells & macrophages
IL-12 secreted by macrophages directs the activation and recruitment of NK cells. IL-12 most effective with a NK Cell Synapse --> direct delivery of IL-12 onto NK cell's surface. iii. IL-15 remains bound to macrophage E surface, also --> NK cell activation, proliferation and survival. iv. Differentiated effector NK cells secrete IFN-γ (Type II interferon) which acts on macrophages
List the inflammatory cytokines released by resident macrophages
IL-1B, TNF alpha, IL6, IL12
Describe the role of inflammasomes in increasing IL-1B secretion by macrophages
IL-1β is made by activated macrophages, which by autocrine feedback amplifies its own synthesis. Its binding stimulates the macrophage to make large quantities of proIL-1β which accumulates in the cytoplasm. Uptake of ATP -->↓ [K+] inflammasome assembly. Inflammasome - consists of NLRP3 (NOD-like receptor lacking a CARD domain), Adaptor Protein (with CARD domain), and procaspase I. Procaspase I is bound by the CARD of the adaptor protein, and becomes oligomerized as the inflammasome assembles, creating a high concentration there --> auto-proteolysis into active caspase I. Caspase I cleaves proIL-1β ---> IL-1β which is secreted
Name 3 cytokines that function as pyrogens.
IL-1β, IL-6, TNF-α
Name cells that dendritic cells interact with in innate immunity & adaptive immunity
In innate immunity, dendritic cells interact with NK cells, whereas in adaptive immunity they turn their attention to T cells.
Describe initiation of the acute phase response.
Increase for some 30 plasma proteins involved in immune response, with decreases in other plasma proteins like albumin. IL-6, and to a lesser extent IL-1β and TNF-α alter plasma protein secretion by hepatocytes
List two main effects of IFN-a & IFN-B on NK-cells.
Induce NK-cell mitosis and proliferation. Induce NK cell differentiation into cytotoxic effector cells that kill virus-infected cells.
IL-1B
Induce blood vessels to become more permeable, enabling effector cells and fluid containing soluble effector molecules to enter the infected tissue
TNF- α
Induce blood vessels to become more permeable, enabling effector cells and fluid containing soluble effector molecules to enter the infected tissue
IL-6
Induces fat and muscle cells to metabolize, make heat and raise the temperature in the infected tissue
Describe the role of TNF-α on neutrophil recruitment
Induces vascular endothelium to express ICAM-1 & ICAM-2 - adhesion molecules that function as ligands for complement receptor CR3 and LFA-1 on neutrophils (integrin adhesion molecules)
Describe how the binding of ICAM-1 & ICAM-2 on endothelium to CR3 and LFA-1 on neutrophils is strengthened and its effect on neutrophil movements
Interactions are weak at first, but binding of CXCL8 to its receptor conformational changes of CR3 and LFA-1 which strengthen their binding with the ICAMs, immobilizing the neutrophil on the vascular endothelial surface.
Explain the general goals of the type I interferon response
Interfere with viral replication by the infected cell. Signal neighboring cells that they should prepare for viral infection. Alert immune system that an infection has occurred. Make infected cells more susceptible to killer lymphocyte attack
Describe the extravasation (diapedesis) process including LFA-1, CR3, CD31, CXCL8, and elastase
LFA-1 and CR3 - bind ICAMs to tightly bind to endothelial surface. CXCL8 - chemotactic agent, strengthens ICAM binding and directs neutrophil movement towards its source (macrophages) within connective tissue. Elastase - secreted by neutrophils, allows it to breach endothelial basement membrane along with other enzymes that degrade the laminins and collagens of the BM. CD31 - cell adhesion molecule needed for diapedesis
In general terms, describe the range of phagocyte receptors present on neutrophils.
LPS receptor (CD14), mannose receptor (CD206): Bacteria-LPS, Cps, ManLam, N-formyl-Met receptor, CR3/CR4, scavenger receptor
Describe the interaction of the two main phagocytes - macrophages & neutrophils
Macrophages are long-lived: reside in the tissues, work from the beginning of infection, raise the alarm, and have functions other than phagocytosis. ii. Neutrophils are short-lived dedicated killers that circulate in the blood, awaiting a call from a macrophage to enter infected tissue, and die within a few hours after entry ---> pus. Arrival of neutrophils is the first series of reactions termed the inflammatory response - cells and molecules of innate immunity are recruited into sites of wounding or infection
Describe the benefits of fever.
Most bacterial and viral pathogens grow and replicate faster at lower temperatures. Adaptive immunity becomes more potent at higher temperatures. Human cells become more resistant to the deleterious effects of TNF-α during fever. Cytokines also induce the lethargy, somnolence, and anorexia that accompany fever, which may represent tactics for fighting infection by not wasting energy on other activity.
List 3 safety features that prevent NK cells from attacking healthy cells
NK cells must have direct contact with target cell (only kill 1 target cell at a time). Kill response made by sum of interaction between many different NK cell receptors. iii. Ground state for NK cell interaction with target cell is active inhibition which must first be overcome by activating receptors before killing can occur
Describe distribution of dendritic cells in the body & their function
Take up pathogens and present them on their cell surface to NK cells. NK cell pathogen recognition strong synaptic interaction
Describe process of formation of phagolysosomes.
Phagosomes fuse with cellular organelles called lysosomes. Acidic vesicles with degradative enzymes and toxic substances for destroying pathogen
Describe difference between plasmacytoid dendritic cells (3-16) and myeloid dendritic cells (3-21).
Plasmacytoid - present in blood and lymphoid tissue, secrete type I IFN (resemble plasma cells). Myeloid - found as resident cells in all tissues of the body, secrete IL-15 (resemble macrophage)
Explain the effect of IFN binding its receptor (IFN response)
Prevent viral replication by activating host genes that destroy viral mRNA and inhibit translation of viral proteins. Increase expression of ligands for NK-cell receptors. Activate NK cells to kill virus-infected cells
Name the 3 types of preformed neutrophil granules & the products contained within each type.
Primary (or azurophilic) granules marked by the presence of the enzyme myeloperoxidase. Secondary (or specific) granules marked by the protein lactoferrin. Tertiary (or gelatinase) granules marked by the enzyme gelatinase
Explain the effect of IFN-γ on macrophages
Primary source of IFN-γ in the innate response is NK cells. --> further macrophage activation = more efficient in phagocytosis and pathogen destruction. IL-12 and IFN-γ create a positive feedback loop that increases strength of the innate response.
Describe the role of NADPH oxidase & role in respiratory burst
Produces superoxide radicals in the phagosome that are converted into hydrogen peroxide by superoxide dismutase --> ↑ pH (7.8-8.0) antimicrobial proteins become active. pH reaches neutrality after 10-15 minutes and lysosomes fuse --> phagolysosome -->↓ pH. Respiratory burst - transient increase in O2 consumption --> products are toxic oxygen species that diffuse out of the cell and damage other host cells. Burst is accompanied by inactivating enzymes like catalase that degrades H2O2
Describe basic structure of toll-like receptor
Protein is a transmembrane polypeptide with a Toll-interleukin receptor (TIR) signaling domain on the cytoplasmic side of the membrane and a horseshoe-shaped sensor domain on the other side.
Describe process of receptor-mediated endocytosis
Receptor-bound pathogen is surrounded by the macrophage membrane and internalized into a membrane-bound vesicle called and endosome or phagosome
Describe how innate immunity cells use receptors to differentiate human cells from pathogens
Receptors expressed by macrophages, NK cells, and others recognize structural features that distinguish microbial carbohydrates, lipids, proteins, and nucleic acids from human counterparts. Recognize bacteria, fungi, viruses, parasites, and unhealthy infected human cells. Each cell contains many different innate immune receptors, each of which can recognize multiple pathogenic species that share a particular type of cell-surface carbohydrate
Explain the benefit of having TLR's on both the plasma membrane & in intracellular locations
Receptors in the first group, which includes TLR4, are located on the plasma membrane and recognize carbohydrate, lipid, and protein structures on the outer surfaces of pathogens. By contrast, receptors in the second group are located inside the cell and in the membranes of endosomes, and recognize features that distinguish the nucleic acids of pathogens from the nucleic acids of human cells
Explain how NOD-like receptors and their CARD domain activate NFkB
Recruit signaling proteins (RIPK2) that have the same type of CARD domain as the NOD receptors and dimerize with it upon ligand (pathogen) recognition ---> RIPK2 activation. RIPK2 (kinase) activates TAKI (kinase) activates IKK activates NFκB
IL-12
Recruits and activates natural killer (NK) cells that in turn secrete cytokines that strengthen the macrophages' response to infection
CXCL8
Recruits neutrophils from the blood and guides them to the infected tissue
Explain how recognition of lipopolysaccharide causes a change in macrophage gene expression
Released by bacteria binds CD14, and forms complex with TLR4 dimer and MD2 ---> cytoplasmic TIR domain of TLR4 binds MyD88 - adaptor protein - brings together two signaling components. Signaling cascade --> activation of IKK (inhibitor of κB Kinase). IKK relieves inhibition of nuclear factor κB (NFκB) by κB (inhibitor of κB). NFκB translocates to nucleus, and initiates transcription of genes for cytokines, adhesion molecules and other proteins necessary to establish inflammatory state in the tissue
Name adhesion molecules/ligand responsible for rolling of neutrophils on the endothelial surface
Selectins (endothelial cells) bind s-Lex glycoproteins (neutrophil surface). These weak interactions slow the neutrophils down relative to the blood flow, causing them to roll along the endothelial surface
Define "cytokine" and explain how these cause changes in a cell.
Small soluble proteins used as a means of communication between cells. In general, cytokines are short-lived molecules that exert their influence within a short distance from the cell that made them, and in some instances the cytokine-secreting cell makes direct contact with the cell it will influence.
Explain how NK cells kill virus-infected cells
Synapse bond strengthens, and NK cell undergoes intracellular cytoskeletal reorganization to facilitate quick, precise, and clean delivery of toxic cargo. Membrane-bound Lytic granules contain enzymes proteins, and proteoglycans --> apoptosis. NK cell detaches, and target cell DNA starts to fragment by the cells own nucleases --> nucleus disrupted --> membrane integrity lost --> cell shrinkage and death
Describe what TLR3 senses & how it leads to IFN‐B production
TLR3 - recognizes double-stranded viral RNA --> production of IFN-β only (via TF activation). Other TLRs (7 & 8) recognize ssRNA synthesis and secretion of IFN-α and IFN-β
Describe two main functions of NK cells in the innate immune response to viral infection
The first is to kill cells infected with virus. This sacrifice of cells hosting the virus impedes virus replication and thus its spread to neighboring cells. The second function of NK cells is to maintain, and even increase, the state of inflammation in the infected tissue. This is achieved by their secretion of inflammatory cytokines that act mainly on the resident macrophages and increase their capacity to secrete inflammatory cytokines and to phagocytose viral particles and microorganisms in the extracellular environment. NK cells thus contribute to defense against both intracellular and extracellular pathogens.
Describe the working definition of a human NK cell by protein expression (CD3(-), CD56(+))
The working definition of a human NK cell is a lymphocyte that expresses CD56, a protein of unknown function expressed by all NK cells, and lacks CD3, a cell-surface protein present on all T cells.
Describe the function/location of plasmacytoid dendritic cells
They are present in the blood, where they comprise fewer than 1% of the total leukocytes, and are also found in the lymphoid tissues but not in other tissues. They are therefore considered to be professional interferon-producing cells.
Describe how RLR's (RIG-I-Like Receptors) can induce secretion of type 1 IFN's & Inflammatory cytokines
Viral replication in cytoplasm produces uncapped RNA with a 5′-triphosphate. RLR binding to viral RNA induces association with MAVS and dimerization. Dimerization initiates signaling pathways that activate. IRF3 and NFκB IRF3 causes synthesis and secretion of type I interferons, and NFκB causes synthesis and secretion of inflammatory cytokines
Explain the sequence of events when a virus infects a human cell (in 1 sentence)
When a virus infects a human cell, it uses the machinery of the cell to transcribe, translate, and replicate its genome, resulting in the presence in the cytoplasm of viral nucleic acids.
Explain how dendritic cells activate NK cells
When one or more NK-cell receptors detects pathogen-induced changes on the dendritic-cell surface, the two cells form a strong interaction with a synapse between them. Signals induced in the dendritic cell lead to the expression of IL-15, which induces NK cells to proliferate, differentiate, and survive.
Define "Lectin"
cell-surface receptors and plasma proteins that recognize carbohydrates
Define the NK-cell synapse & its function
immunological synapse that helps hold the cells together through which information and material can be exchanged. Interacting sets of receptors and ligands concentrate in specific lipid rafts