Pre-existing innate immunity Flashcards
What lineage are NK cells derived from?
Lymphoid lineage (as are T and B cells)
However, unlike T/B cells, NK cells do not react to specific pathogens
How do NK cells recognize intracellular pathogen-infected cells or tumor cells?
By using the imbalance between target cell surface MIC (higher) and MHC class I proteins (lower)
Or the presence of IgG bound to the target cell surface
How do NK cells kill target cells?
By using perforin and granzyme to induce target cell apoptosis
What type of molecular signals do neutrophils respond to?
PAMPs and chemokines
What is typically the first leukocyte to enter an infection site?
Neutrophils
Function of activated neutrophil
Killing extracellular microbial pathogens:
Adhere and phagocytose unicellular microorganisms - afterward - cytoplasmic ganules fuse w/ the phagosome and the microorganism is killed by anti-microbial effectors
Also kills by releasing granule contents and reactive chemical species into the extracellular milieu to kill non-phagocytosed pathogens at site of infection (also contributes to tissue damage)
Stimulate wound healing
Major innate immune cells that kill unicellular bacteria and fungi
Does a neutrophil restore its granules after discharging?
No, once they are fully discharged, the nuetrophils die
Dead neutrophils contribute to the formation of pus
Band cells
CBC
Immature neutrophils
Increased band cells (left shift) indicate the a Pt has suffered a strong, often acute, inflammatory/infectious insult
Seg cells
CBC
Mature neutrophils
Increased segs often indicates ongoing bacterial or fungal infection
Macrophages
How do neutrophils and macrophages differ in function?
Macrophages continuosly recharge their lysosomes w/ anti-microbial compounds and do not die after killing microorganisms
Macrophages also bind both PAMPs and DAMPs
What is the fate of the phagosome after neutrophils/macrophages ingest a pathogen?
Fusions with the lysosome to kill pathogen with toxic lysosomal contents
Endocytic PRR’s expressed by macrophages/neutrophils
Opsonins
Bind to microbial surfaces, including encapsulated microbes
IgG and C3b are important opsonins
Mucus
Branched glycoprotein polymer made by mucosal goblet cells
Major function - retain water and keep mucosal epithelium moist
Binds IgA and anti-microbial peptides (AMPs)
IgA - neutralizes
AMPs - kill
What activates neutrophils?
Local inflammation induced by PAMP stimulated macrophages and mucosal epithelia
Pseudomembranous enterocolitis
C. diff secretes toxin that compromises integrity of the gut lining
Cationic anti-microbial peptides
Defensins
Histatins
Cathelicidins
Found in sweat, tears, and mucosal secretions
Many secreted by mucosal epithelium and Paneth cells
Others are made by macrophages and neutrophils
Forms pores and cause osmotic lysis of target cells
C-reactive protein
CRP - secreted from the liver into the blood/lymph and opsonizes pathogens
Lysozyme
Enzyme that degrades PPG
Found in tears, saliva, CSF, and is secreted by mucosal Paneth cells
Neutrophils also release lysozyme into tissues when they migrate to site of infection
Complement pathways
Alternative path
Lectin path
Classical path
Initiated differently but all three merge at the step where the C3 complement protein is cleaved into fragments C3a and C3b
C3b
Chemically reactive opsonin (macrophages and nuetrophils have surface C3b receptors)
Binds to pathogen surface and marks it for destruction - opsonization or stimulation of the membrane attack complex (MAC)
Pro-inflammatory mediators of the complement pathway
C3a
C4a
C5a
Induce inflammation in infected tissues where the cascades are activated
What activates the classical complement pathway?
Antibody or CRP binding to the surface of a pathogen
CRP binds to phosphocholine in bacterial and fungal cells walls (not to human phosphocholine)
At least two adjacent Ab Fc regions are required for activation - 1 IgM pentamer, 2 IgG molecules, or CRP bind to complement factor C1qrs
C1qrs
Binds to IgG, IgM, or CRP
Cleaves C4 and C2 into their a/b componenets
C4b
Binds to the pathogen surface, then binds C2a forming the classical C3 convertase (C4b2a)
Classical C3 convertase
C4b2a - cleaves C3 into its a/b componenets
C3b
Binds to the target cell surface to either acts as an opsonin or to complex w/ the classical C3 convertase to form the classical C5 convertase (C4b2a3b)
Classical C5 convertase
C4b2a3b - cleaves C5 into a/b components to start MAC formation
What activates the lectin complement pathway?
Mannose binding lectin (MBL) binding to mannose-containing surface structures on microorganisms
Mannose-binding lectin
Acute phase protein produced by the liver that is found in the bloodstream after an inflammtory insult
MBL-associated serine proteases (MASPs)
Part of the lectin complement pathway activation
MASPs cleave C4 and C2 - after which C4b attaches to pathogen surface and binds C2a forming the classical C3 convertase (C4b2a)
iC3
Initiates the alternative complement pathway - C3 spontaneously hydrolyzes into C3(H2O) = iC3
Rate of C3 hydrolysis is increased by LPS and other pathogen surface componenets
iC3 binds factors B and D
The alternative complement pathway
What induces factor B cleavage in the alternative complement pathway?
Binding of iC3 (C3H2O) to factors B and D -D then cleaves B
Produces Bb and Ba and yields soluble C3 convertase = C3(H2O)Bb which cleaves C3 into C3a/C3b
C3b binding to pathogen surface binds more factors B and D
C3bBb
Alternative C3 convertase
C3b2Bb
Alternative C5 convertase - cleaves C5 into a/b components to start MAC formation
MAC formation
What types of pathogens are C3 deficient patients susceptible to?
Encapsulated bacterial species (i.e. Streptococcus pneumoniae)
Becuase of C3b opsonization is important in killing encapsulated pathogens early during infection before IgG is made
Most severe form of complement deficiency
What type of pathogens are patients with deficiencies in MAC componenets susceptible to?
They are susceptible to systemic infections by bacteria in the genus Neisseria (Gram -)
These Pt’s typically present after age of ten w/ recurrent episodes of N. meningitidis infections
CR1
Expressed primarily on macrophages, neutrophils, and erythrocytes
Binds to C3b
Phagocytosis or to protect RBCs from complement by inhibiting convertase formation
C3a/C4a/C5a receptors
Expressed on mast cells, macrophages, and neutrophils (along with others)
Binding to C3a or C5a activates release of inflammatory mediators from mast cells and macrophages
Neutrophil chemotaxis toward site of complement activation
Major biologic functions of complement pathways
Cytolysis (MAC formation)
Opsonization (C3b)
Inflammation (C3a/C5a)
Immune complex removal
Where are immune complexes deposited if unable to be removed?
Within areas of high pressure - microvasculature of the kidney glomeruli, joints, and skin
Characterize immune complex disease
Fever
Acute kidney injury
Skin rash
Joint swelling and pain
Clot formation
SLE - immune complexes cause these issues
Passive regulation of complement
C3 and C5 convertases are unstable and active for only a short time after assembly - do not stay activated unless constantly stimulated by Ab/CRP binding, MBL binding, or present of bacterial cell wall components (i.e. LPS)
C1 esterase
aka C1 inhibitor
Soluble in serum
Binds C1 and blocks classical complement cascade initiation
Only classical pathway
Factor H/I
Regulates all complement pathways
Soluble in serum
Bind and cleave C3b = and all convertases that contain C3b
Most important for turning off alternative pathway in absence of paths
Decay accellerating factor (DAF/CD55)
Membrane bound host cell protein
Bind C3b and blocks all C3 and C5 convertases containing C3b
Protects host cell surfaces from C3b opsonization and MAC by all pathways
Membrane inhibitor of reactive lysis
MIRL/CD59
Host cell membrane bound
Binds MAC and prevents C9 polymerization
Paroxysmal nocturnal hemoglobinuria
CD55/DAF or CD59/MIRL deficiency
Results from mutations in the PIGA (phosphatidylinositol glycan class A) gene and prevents addition of GPI (glycosyl phosphatidylinositol) anchors to host cell membrane-bound compliment inhibitory proteins CD55/DAF and CD59/MIRL during hematopoeisis
CD55/DAF and CD59/MIRL are no longer tethered to RBC membranes
Pt’s present w/ episodic dark-colored uring (particularly in the morning) fatigue, tachycardia, and SOB - all due to anemia and reduced O2 saturation
Lab test to assess complement pathway function
CH50 and AH50 tests
CH50 - assays classical and alternative complement pathway function combined
AH50 - assays only alternative complement pathway function (Mg2+ - EGTA buffer inhibits classical pathway activation)
If deficiency is indicated - antigen-capture ELISA will be used to determine which complement factor is lacking
Leukocyte Adhesion Deficiency Type 1
-Due to defective beta-2-integrins (CD18)
-Results in recurrent skin/mucosal infections without purulence
-Delayed umbilical cord separation
-Peripheral leukocytosis
May present w/ loss of adult teeth by adolescence due to periodontitis
Chediak-Higashi Syndrome
Caused by a defective lysosomal trafficking regulator gene (mutated LYST gene)
Immunodeficiency - recurrent infections w/ pyrogenic bacteria (i.e. LPS secreting Gram-)
Oculocutaneous albinism
Neurologic abnormalities
Giant lysosomal granules w/i WBCs
Chronic granulomatous disease
Recurrent infections by catalase-positive organisms w/ normal immunoglobins and no leukopenia:
Staphylococcus aureus
Kurkholderia cepacia
Serratia marcescens
Norcardia
Asperigullus
X-linked disorder
Results from neutrophils having and impaired respiratory burst secondary to defective NADPH oxidase
Nitroblue tetrazolium test - dx CGD and check NADPH oxidase activity
Absence of fluorescence on dihydrohodamine flow cytometry can also dx (dihydrorhodamine is normally oxidized and fluoresces green)
Myeloperoxidase Deficiency
Myeloperoxidase - enzyme in cytoplasm of neutrophils that catalyzes production of hypochlorite from H2O2 and Cl-
Usually asymptomatic but may cause invasive Candida infections
Green discoloration of pus or sputum seen during common bacterial infections is due to the presence of myeloperoxidase
Terminal complement deficiencies
Inability to form MAC - Pt’s susceptible to infections with Neisseria species
Evaluation will show decreased activity of the classical (CH50) complement cascade and of the alternative (AH50) cascade
Deficiency of complement factor C3
Associated w/ recurrent pyogenic infections due to impaired opsonization of bacteria
Hereditary angioedema
Characterized by recurrent episodes of cutaneous and mucosal swelling due to a deficiency of C1 inhibitor along with low levels of serum C4
Deficiency of what complement factor leads to excess production of bradykinin?
A deficiency of C1 inhibitor
Excess production of bradykinin produces angioedema
Histologic characterization of granulomas
Aggregates of activated macrophages that assume an epithelioid appearance (epithelioid macrophages)
Epithelioid macrophages may fuse together to form multinucleated cells (Langhans giant cells) surrounded by a rim of Th1 lymphocytes
CD14
A monocyte marker
Stains the activated epithelioid macrophages that form granulomas
Non-caseating granulomas
Lack a central area of necrosis - i.e. sarcoidosis
Result of increased 1-alpha-hydroxylase activity in macrophages
Hypercalcemia - increased 1-alpha-hydroxylase activity increases vitamin D formation
Four stages of wound healing
- Hemostasis (fibrin clot formation)
- Inflammation (cellular infiltration)
- Proliferation (reepithelization, fibroplasia, and angiogenesis)
- Maturation (collagen remodeling)
Tumor necrosis factor-alpha
Proinflammatory cytokine secreted primarily during the inflammatory phase of wound healing
When does the proliferation phase of wound healing occur?
3 days to 5 weeks after injury
Characterized by angiogenesis - stimulated by FGF and VEGF and the deposition of type III collagen
What characterizes granulation tissue
Proliferating capillaries and fibroblasts
Remodeling (maturation) stage of wound healing
Occurs between 3 weeks and 2 years after injury
Type I collagen is the primary collagen in mature scar tissue (also present in bones, tendons, ligaments, and skin)
Myofibroblasts and metalloproteinase secretion is important for wound contraction
Healing by first intention
Involves limited granulation tissue formation (minimal scar formation and no wound contraction)
Keloids
Large, irregular masses that result from excessive deposition of type I and type III collagen in dermis due to the excess production of transfroming growth factor-beta (TGF-β) by fibroblasts
More commong in African Americans - typical site being earlobes
Increased prod. of hyalinized collagen
Histologic characterization of keloid scars
Abnormally broad, disorganized eosinophilic bands of collagen in the dermis
Hypertrophic scars
Result from localized excess production of scar tissue (increased type III collagen) due to excess production of transforming growth factor-beta (TGF-β)
Histologically - parallel organized arrangement of collagen in dermis
Dupuytren contracture
Consists of fibroblastic proliferation and thickening of the palmar fascia (palmar fibromatosis)
Characterized by inability to extend the fourth and fifth fingers
Fibrotic nodules and cords forming along the flexor tendons that limit the extension of the affected digits are pathognomonic
Congenital torticollis
Unilateral fibrosis of sternocleidomastoid muscle - often caused by intrauterin malposition of the fetal head - may be associated w/ a large body (fetal macrosomia) or decreased amniotic fluid (oligohydraminios)
Contraction of the sternocleidomaastoid muscle causes head to tilt toward affected muscle - chin points away from affected muscle
What is the most common localized form of fibroblast proliferation?
Dupuytren contracture
Peyronie disease
Penile fibromatosis - curved penis due to localized proliferation of fibroblasts on the dorsolateral aspect
During tissue repair, what connective tissue is deposited first?
Type III collagen (by fibroblasts) and then it is replaced by type I collagen
Transforming growth factor alpha (TGF-ɑ)
Promotes epithelial cell proliferation, growth, and differentiation
Transforming growth factor-beta (TGF-β)
Stimulates proliferation of fibroblasts and smooth muscle cells
Also decreased degradation of extracellulalar matrix by metalloproteinases in the skin following an injury
Platelet derived growth factor (PDGF)
Found in alpha granules of platelets
Stimulates the proliferation of fibroblasts, smooth muscle cells, and monocytes
PDGF in excess can cause fibrosis of bone marrow (myelofibrosis)
IL-12
Secreted by macrophages to induce CD4+ helpter T cells to differentiate into TH1 cells
What cytokines are secreted by Th1 cells
Interfereon gamma
Interleukin-2
Proinflammatory
Cytokines secreted by Th2 cells
IL-4
IL-5
IL-6
IL-10
IL-13
What cytokine converts macrophages to epithelioid cells?
INF-gamma
why anti-TNF therapy can cause disseminated TB
Basophils
Leukocyte with numerous deeply basophilic granules w/i cytoplasm that completely hide nucleus
Have surface receptors for IgE
Release histamine
Basic protein
Secreted by eosinophils - toxic to helminthic parasites
Arylsulfatase
Released by eosinophils - neutralizes leukotrienes
What cell secretes histaminase?
Eosinophils
WBCs involved in chronic inflammation
Often associated w/ increased numbers of monocytes and lymphocytes, but eosinophils and basophils are also types of chronic inflammatory cells
Neutrophils with more than five nuclear lobes
Hypersegemented, think megaloblastic anemia
What normally inactivates bradykinin?
ACE - why you cannot give ACE inhibitor (i.e. captopril) to Pt w/ C1 esterase inhibitor deficiency
Familial Angioedema
Familial angioedema
Deficiency of C1 esterase inhibitor
Episodic nonpitting edema of soft tissue (esp the lips)
Severe abdominal pain and cramps - occasionally accompanied by vomiting - may be caused by edema of GI tract
C1 esterase inhibitor prevents conversion of prekallikren and kininogen to bradykinin -
Deficiency of C1 esterase inhibitor leads to excess production of bradykinin and increased vascular permeability - stimulates smooth muscle contraction, dilates blood vessels, and causes pain
ACE inhibitors contraindicated since ACE inactivates bradykinin
CD18
beta-2-integrins - leukocytes adhesion and transmigration during acute inflammation
Deficiency - neutrophils won’t be found at sites of infection (no pus)
Which is the most important cell type for initiating inflammatory responses in tissues?
Macrophages - resident in tissue - recruit nuetrophils
PAMPs bind PRR and induce inflammation - secrete cytokines/chemokines
What complement pathway does LPS induce?
The alternative pathway
What deficiency is indicated by recurrent Neisseria infections of the same Pt?
Late complement deficiency (MAC assembly - C3 and later)
Which complement cascade pathway is responsible for clearing immune complexes once activated?
The classical complement pathway
Therefore, C1q/C2/C4 deficiencient patients are at increased risk for developing systemic erythematous lupus
Leukocyte adhesion deficiency
Leukocyte adhesion deficiency, which is due to defective beta-2-integrins (CD18), is characterized by failure of leukocyte adhesion and migration and results in recurrent skin and mucosal infections without purulence, delayed umbilical cord separation, and peripheral leukocytosis.
Mutations involving LYST
Chediak-Higashi syndrome, which is caused by a defective lysosomal trafficking regulator gene (mutated LYST gene), is characterized by immunodeficiency (recurrent infections with pyogenic bacteria), oculocutaneous albinism, neurologic abnormalities, and giant lysosomal granules within white blood cells.
Defect involving NADPH oxidase
Chronic granulomatous disease, which is characterized by recurrent infections by catalase-positive organisms with normal immunoglobulins and no leukopenia, results from neutrophils having an impaired respiratory burst secondary to defective NADPH oxidase.
Terminal complement deficiencies (C5-C9) result in inability to form the membrane attack complex, which renders affected patients more susceptible to infections with what pathogenic species.
Neisseria
INF-gamma
Non-caseating granulomas, which lack a central area of necrosis, can be found in multiple different clinical disorders, such as sarcoidosis. Th1 cells produce IL-2 and interferon-gamma, which promote further T-cell response, activation of macrophages, and differentiation of macrophages into giant cells. INF-gamma converts macrophages to epithelioid cells, which forms granulomas, while IL-2 stimulates the autocrine proliferation of Th1 cells.
Inheritance pattern of chronic granulomatous disease
X-linked recessive
Dihidrordamine Test
Meaures NADPH oxidase activity - not concentration of neutrophils
Low NADPH oxidase activity - multiple granulomas and chronic infection w/ Aspergillus (Aspergillus pneumonia)
What types of viruses does TLR3 detect?
All RNA viruses (even ssRNA - becomes dsRNA when it reproduces)
Healing by secondary intention
Larger defects that heal w/ granulation tissue formation and possible scar contraction (mediated by myofibroblasts)
Caseating granulomas
Characteristic of certain fungal infections and tuberculosis (classic infectious granulomatous disease)
