Inflammation and Innate Immunity (part I)

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Inflammation and Innate Immunity (part I)

• Inflammation
• Innate immunity and the initial response to
  infection
• Cytokines that induce inflammation and direct
  inflammatory cells
• Recognition of microbes by Toll-like receptors
  (TLRs) and other innate recognition elements
• Inflammation and recruitment of phagocytes
• Uptake and killing of bacteria by phagocytes
• Innate immunity against fungi, helminths, at
  mucosal epithelium

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Inflammation

• Source Wikipedia

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Inflammation

• rubor et tumor cum calore et dolore
• (redness and swelling with heat and pain)
• --Cornelius Celsus in De Medicina, 1st century
  A.D.
• later functio laesa (disturbance of function)
  was added

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Inflammation

• rubor et tumor cum calore et dolore
• (redness and swelling with heat and pain)
• --Cornelius Celsus in De Medicina, 1st century
  A.D.
• later functio laesa (disturbance of function)
  was added

Inflammation is an adaptive response to noxious
conditions (infection and tissue injury)--an
attempt to restore homeostasis
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Inflammation

• Inflammation can be induced by immune recognition
  of infection or tissue damage (usually good)
• Inflammation can be induced by immune recognition
  that is hypersensitive to environmental
  components or autoinflammatory or autoimmune
  (disease)

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Inflammation

• Inflammation can be induced by immune recognition
  of infection or tissue damage (usually good)
• Inflammation can be induced by immune recognition
  that is hypersensitive to environmental
  components or autoinflammatory or autoimmune
  (disease)
• Acute inflammation influx of white blood cells
  and fluid from blood to fight infection and aid
  tissue repair
• Chronic inflammation inducer of inflammation is
  not removed
• Leads to tissue damage and loss of tissue
  function (joint destruction, lung fibrosis, etc.)
• Current view aggressively fight inflammation in
  certain chronic diseases to decrease/delay
  progressive loss of function

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Inflammation

• Inflammation can be induced by immune recognition
  of infection or tissue damage (usually good)
• Inflammation can be induced by immune recognition
  that is hypersensitive to environmental
  components or autoinflammatory or autoimmune
  (disease)
• Acute inflammation influx of white blood cells
  and fluid from blood to fight infection and aid
  tissue repair
• Chronic inflammation inducer of inflammation is
  not removed
• Leads to tissue damage and loss of tissue
  function (joint destruction, lung fibrosis, etc.)
• Current view aggressively fight inflammation in
  certain chronic diseases to decrease/delay
  progressive loss of function
• Current research suggests that inflammation may
  play an important role in common chronic diseases
  including atherosclerosis, type 2 diabetes,
  neurodegeneration, and cancer

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Immune sentinel cells in the tissues dendritic
cells
Green dendritic cells Blue nuclei of all cells
Langerhans cells (epidermal dendritic cells) in
the skin WJ Mullholland et al. J. Invest.
Dermatol. 126 1541, 2006.
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Infection leads to production of inducers of
inflammation
or dendritic cell
Inflammatory mediators Complex and many, but
include Lipids and Proteins (cytokines/chemokines
)
TNF
Others
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Cytokines

• Cytokines are soluble protein mediators
  secreted by immune cells (mostly) that act on
  other cells to regulate their activity many are
  called interleukins (IL-1, IL-2, etc.) (note
  sometimes exist in cell-bound forms)
• Cytokines have many functions, well focus on a
  few central functions of some key cytokines (see
  Cytokine primer in syllabus/on iROCKET)
• Name of a cytokine often doesnt reflect its most
  important function (TNF stands for tumor
  necrosis factor but main function is to induce
  inflammation)
• A subfamily of cytokines primarily functions in
  directing migration of cells, these are called
  chemotactic cytokines or chemokines
• Chemokines have systematic names CCL1, 2, and
  CXCL1, 2,
• (but older names sometimes used, including IL-8)

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The Initial Response to Infection Innate Immunity

• Recognition of infection by hard-wired
  recognition molecules or recognition of tissue
  damage and cell death, danger
• Rapid mobilization of leukocytes to the site of
  infection and influx of plasma into the tissue
  site. (inflammation)
• Recruited innate immune cells kill
  microbes/virally infected cells (also can promote
  tissue repair but when dysregulated can
  exacerbate tissue injury)
• Also, innate recognition promotes the adaptive
  immune response, which is slower but more
  powerful

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Cytokines and Inflammation

• Macrophages or DCs stimulated via innate immune
  receptors make pro-inflammatory cytokines,
  especially TNF (Tumor necrosis factor), IL-1, and
  IL-6
• TNF and IL-1 signal to endothelial cells to make
  them
• Leaky to fluid (influx of plasma containing
  antibodies, complement components, etc.)
• Sticky for leukocytes, leading to influx of first
  neutrophils, later monocytes, lymphocytes
• IL-6 promotes adaptive immune responses and has
  systemic effects (acute phase response of
  liver, including C-reactive protein or CRP
  levels used clinically as an indication of
  systemic inflammation)

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Leukocyte recruitment to sites of inflammation
or DC
See Abbas and Lichtman Fig. 2-7
Note molecular details of leukocyte
extravasation will be covered in lecture Friday
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Inflammation Neutrophils vs. Monocytes

• Acute inflammation is initially characterized as
  rich in neutrophils later it is more monocytes
  and lymphocytes. This is controlled by which
  chemokines are expressed by the endothelial cells
  and by T cells.
• Neutrophils are dedicated to killing microbes and
  are short-lived. They often damage host tissue
  as a byproduct.
• Monocytes are multi-potential, depending on
  cytokine signals
• IFN-g assume a vigorous killing phenotype
  similar to neutrophils
• IL-4 alternatively activated macrophages
  tissue repair, barrier immunity
• IL-10 assume a wound-healing type phenotype
  (to clean up after infection is cleared)
• GM-CSF assume a dendritic cell phenotype and
  propagate adaptive immune responses

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Anti-Inflammatory Therapeutics

• NSAIDs inhibitors of inflammation and fever
  (block prostaglandin synthesis)
• Glucocorticoids are also potent anti-inflammatory
  drugs natural systemic anti-inflammatory
  mechanism
• Agents that block TNF are effective in treating
  rheumatoid arthritis, Crohns disease, etc.
• Agents that block IL-1 are less effective for
  these diseases but are useful for some genetic
  inflammatory diseases (and are currently in
  clinical trials for more common conditions)

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How is infection first recognized by the immune
system?

• What is seen by innate immunity?
• Microbes evolve rapidly, so innate immunity must
  focus on highly conserved and essential
  components of microbes (cell wall structures
  nucleic acids). So-called Pathogen-associated
  molecular patterns (PAMPs)
• What mediates the recognition?
• Diverse recognition elements 4 key families of
  cellular receptors
• Toll-like receptors (TLRs transmembrane
  receptors)
• C-type lectin receptors (CLRs transmembrane
  receptors)
• RigI-like receptors (RLRs cytoplasmic RNA
  helicases)
• NOD-like receptors (NLRs cytoplasmic sensors)
• Also, recognition of molecules released from
  necrotic cells, tissue damage (damage-associated
  molecular patterns DAMPs or danger).
  Recognized by same families of innate receptors
  as PAMPs (Notetissue damage can also be
  recognized by pain neurons, which can promote
  inflammation)

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TLRs Toll is required for innate defense in flies
J. Hoffmann et al. Cell 1996
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Toll-like receptors and recognition of pathogens
ssRNA
K. Takeda S. Akira, Cell. Microbiol. 5 143-53,
2003
Red circles You should know these ligand/TLR
pairs
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-Cell surface TLRs recognize bacterial cell wall
structures-IntracellularTLRs recognize pathogen
nucleic acids-Location likely aids
discrimination of viral vs. host nucleic
acids(likely connection with SLE)
Cellular localization of Toll-like receptors
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The transcriptional activator NF-kB is a key
player in inflammatory cytokine expression
or TLR or IL-1
IKK I-?B kinase
(Classical Pathway)
Proteasome degrades I-?B
(Potential therapeutic target)
Genes regulated Inflammatory cytokines,
chemokines, immune effector molecules, cell
survival factors
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Sepsis Syndrome very bad(too much of a good
thing)

• Bacterial septicemia leads to activation of TLRs
  on monocytes in the blood, DCs in spleen
• Systemic release of TNF and IL-1 leads to
  inflammation all over the body
• Shock from loss of blood pressure (vasodilation
  and leakage of fluid into tissues)
• TLRs also induce coagulation (via tissue factor)
• Current therapy with some efficacy activated
  protein C promotes fibrinolysis, breaks down
  thrombi
• The combination of effects frequently leads to
  multi-organ failure and death

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Innate recognition by CLRs (examples)
Geijtenbeek and Gringhuis, Nat. Rev. Immunol. 9
465, 2009
NF-?B
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Innate recognition in the cytoplasmNLRs and RLRs
Modified from Abbas and Lichtman Fig. 2-2
Inflammatory cytokines
Secrete anti-microbial peptides into lumen of
crypts of sm. intest.
(Mda5)
Engulfment of bacteria invading the cytoplasm
(autophagy)
Interferon-?
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Common alleles of NOD2 are a genetic risk factor
for Crohns disease

• Several moderately common alleles of the NOD2
  gene (7 of total alleles) increase
  susceptibility to Crohns disease (a form of
  inflammatory bowel disease)
• Two copies of these alleles increase
  susceptibility by 40X
• Mechanism most evidence indicates these are
  loss-of-function alleles unknown which function
  of NOD2 is most relevant

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Processing of IL-1 and related cytokines an
important regulatory step

• Some NLRs assemble to form the inflammasome
  which proteolytically processes IL-1 and related
  cytokines (IL-18) to their active, secreted
  forms.
• Inflammasome in activated by cellular stress or
  recognition of microbial components in the
  cytoplasm

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Processing of IL-1 and related cytokines an
important regulatory step

• Some NLRs assemble to form the inflammasome
  which proteolytically processes IL-1 and related
  cytokines (IL-18) to their active, secreted
  forms.
• Inflammasome in activated by cellular stress or
  recognition of microbial components in the
  cytoplasm
• Genetic periodic fever syndromes are due to
  activating mutations in the inflammasome (active
  when it shouldnt be)
• Inflammasome is activated by some types of small
  crystals that can be phagocytosed by macrophages,
  important role in Gout

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The NALP3-inflammasome activates caspase 1 in
response to cellular insults
Phagocytosed crystals Bacterial pore-forming
toxins Efflux of K Bacterial flagellin Other
insults/stresses

• Combinatorial Regulation of IL-1
• TLRs and NOD1/NOD2 induce synthesis of pro-IL-1
• Inflammasome processes it to generate active IL-1

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Inducers of Inflammation

• Ligands for TLRs, NOD1/2 or CLRs DCs,
  macrophages makeTNF and IL-1
• Virus infections infected cells, pDCs make
  IFN?/? (type 1)
• Tissue damage (cell necrosis etc.) DAMPs
  activate DCs, macrophages probably via TLRs,
  CLRs, inflammasomes (other receptors?)
• Complement fragments (innate activators or IgM or
  IgG antigen)
• Mast cell activation (IgEallergen or innate
  mechanisms release histamine, leukotrienes,
  cytokines) eosinophil-rich inflammation (type 2
  immunity)
• Effector T cells responding to antigen (TNF
  other cytokines chemokines)
• -the 3 types of effector T cells induce
  inflammation of different characters (what white
  blood cells attracted)

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Negative Regulation of Inflammation

• Cells responding to innate stimuli stop making
  inflammatory mediators after short time period
  and convert to making anti-inflammatory lipids
  (resolvins, etc.) and anti-inflammatory cytokines
  (IL-10, TGF-?)
• But incoming inflammatory monocytes can still
  respond to stimuli if present and continue
  inflammation
• Killing the infectious agent and removal of the
  dead cells, debris, crystals, etc. will stop
  stimulation of incoming inflammatory cells
• Systemic elevation of inflammatory cytokines
  (esp. IL-1) induce production of glucocorticoids,
  which are anti-inflammatory (also by stress)
• Regulatory T cells are also anti-inflammatory,
  both by blocking effector T cells and by
  inhibiting innate cells

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Leukocyte recruitment to sites of inflammation
neutrophils are good at killing microbes
or DC
See Abbas and Lichtman Fig. 2-7
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Phagocytosis and Killing of Microbes
Abbas and Lichtman Fig. 2-9
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Phagocytosis and Killing of Microbes

• Key Concepts related to phagocytosis
• Opsonization soluble immune recognition
  elements tag a particle for phagocytosis
  (opsonins include IgG, C3b, Mannose-binding
  lectin, etc.)
• Interferon-? from NK cell or Th1 cell promotes
  killing of internalized microbes by
  monocytes/macrophages
• Killing mechanisms ROI, NO, proteases,
  anti-microbial peptides

Abbas and Lichtman Fig. 2-9
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Phagocytosis and Killing of Microbes

• Key Concepts related to phagocytosis
• Opsonization soluble immune recognition
  elements tag a particle for phagocytosis
  (opsonins include IgG, C3b, Mannose-binding
  lectin, etc.)
• Interferon-? from NK cell or Th1 cell promotes
  killing of internalized microbes by
  monocytes/macrophages
• Killing mechanisms ROI, NO, proteases,
  anti-microbial peptides

Genetic defects in phagocyte oxidase components
chronic granulomatous disease
Abbas and Lichtman Fig. 2-9
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Innate Immunity against fungal pathogens

• CLRs are key innate recognition elements for
  fungi/yeast (TLRs can also play a role)
• Neutrophils are important for killing most fungal
  pathogens
• Some fungal pathogens can establish intracellular
  infections (like some bacterial pathogens)
  interferon-? is important for defense often also
  NO

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Innate Immunity against helminths

• Often multicellular parasites induce a type 2
  inflammation characterized by influx of
  eosinophils and basophils instead of neutrophils
  and monocytes
• This type of inflammation is also seen in asthma
  and allergies, as will be discussed later in the
  course and can be propagated by Th2 adaptive
  immunity and/or IgE
• Innate recognition is not yet understood, may
  include foreign polysaccharides (chitin),
  proteases, tissue damage
• In some parasitic worm infections inside tissue,
  bacteria in the gut/feces of the worm stimulate
  TLRs and neutrophil-rich inflammation, which can
  cause pathology (African river blindness)

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Innate Immunity and Mucosal Epithelium

• Microbes are tolerated outside mucosal epithelium
  when consistent with its function (colon upper
  airways)
• Efforts to keep microbes out of some mucosal
  epithelial regions (small intestines and small
  airways)
• Mechanisms include actions of some surfactant
  proteins in lungs (bind to foreign
  polysaccharides) secretion of anti-microbial
  peptides by Paneth cells in crypts of small
  intestines secretion of mucus by goblet cells
  ?? T cells in epithelial tissue IgA
• IL-13 is an important cytokine promoting mucus
  secretion

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Tomorrow Innate Immunity to Viruses