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SFM > Complement Immune System > Flashcards

Complement Immune System Flashcards

1
Q

What are the general “5 steps” of alternative complement system?

A
  1. initiation of complement activation
  2. C3 cleaved: C3a inflammation
  3. C3b deposited on microbe: opsonization and phagocytosis
  4. C5 cleaved: C5a inflammation
  5. membrane attack complex (MAC): lysis of microbe
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2
Q

What other medically important proteolytic cascades does complement system cooperate with? (2)

A
  • blood coagulation pathways
  • kinin-kallikrein system: regulates vascular permeability
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3
Q

What does Factor B do in alternative complement system?

A
  • Bb is a serine protease
  • active enzyme of C3 and C5 convertases
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4
Q

What does Factor D do in alternative complement system?

A
  • plasma serine protease
  • cleaves factor B when it is bound to C3b
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5
Q

What does properdin (Factor P) do in alternative complement system?

A
  • stabilizes C3 convertases (C3bBb) on microbial surfaces
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6
Q

What does C1 do in classical pathway?

A

initiates the pathway

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7
Q

What does C1q do in the classical pathway?

A

binds to Fc portion of antibody that has bound to microbe antigen, to apoptotic cells, or to cationic surfaces

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8
Q

What does C1r do in classical pathway?

A
  • serine protease
  • cleaves C1s to make it an active protease
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9
Q

What does C1s do in classical pathway?

A
  • serine protease
  • cleaves C4 and C2
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10
Q

What does C4 do in classical pathway?

A
  • C4b covalently binds to microbe, complement is activated
  • C4b binds C2 for cleavage by C1s
  • C4a: unknown
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11
Q

What does C2 do in classical pathway?

A
  • C2a is a serine protease
  • active enzyme of C3 and C5 convertases to cleave C3 and C5
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12
Q

What composes the classical C3 convertase?

A

C4bC2a

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13
Q

What composes the classical C5 convertase?

A

C4bC2aC3b

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14
Q

What does MBL do in lectin pathway?

A

agglutinin, opsonin, complement fixing

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15
Q

What does MASP1 do in lectin pathway?

A

forms complex with MASP2 and collectins for ficolins and activates MASP3

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16
Q

What does MASP2 do in lectin pathway?

A

forms complex with lectins, especially ficolin-3

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17
Q

What does MASP3 do in lectin pathway?

A

associates with collectins or ficolins and MASP1, cleaves C4

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18
Q

What is the activation requirement for classical pathway?

A
  • antibodies: 1 IgM or 2 IgG
  • C1
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19
Q

What is the activation requirement for lectin pathway?

A
  • does not use C1
  • bacteria/pathogen needs to have mannose antigen
  • MBP binds to bacteria, MASPs are activated
20
Q

What is the activation requirement for alternative pathway?

A
  • C3 undergoes spontaneous hydrolysis
  • FB and FD are needed
21
Q

What does C1-inhibitor do in the regulation of complement pathways?

A
  • inactivates C1r, C1s (classical) and MASPs (lectin) (all irreversible)
  • also inhibits kallikrein-kinin and coagulation cascades (complement activation)
22
Q

What does Factor 1 (F1) do in the regulation of complement system?

A
  • inactivates/degrades C3b and C4b (inhibits formation of convertases)
  • requires cofactor activity by one of the following: MCP, CR1, Factor H, C4BP
23
Q

Which regulatory proteins destabilize CP C3 convertase? AP C3 convertase?

A
  • CP C3: DAF, CR1, C4BP
  • AP C3: DAF, CR1, Factor H
24
Q

Which regulatory proteins inhibit MAC assembly?

A

CD59, S protein, vitronectin

25
Q
  • disease caused by complement deficiency
  • immune-complex disease
A

C1, C2, C4

26
Q
  • disease caused by complement deficiency
  • susceptibility to capsulated bacteria
A

C3

27
Q
  • disease caused by complement deficiency
  • susceptibility to Neisseria
A

C5-C9

28
Q
  • disease caused by complement deficiency
  • susceptibility to capsulated bacteria Neisseria but no immune-complex disease
A

Factor D, properdin (factor P)

29
Q
  • disease caused by complement deficiency
  • similar affects to deficiency of C3 (suspectibility to capsulated bacteria)
A

Factor I deficiency

30
Q
  • disease caused by complement deficiency
  • autoimmune-like conditions including paroxysmal nocturnal hemoglobinuria
A

DAF, CD59

31
Q
  • disease caused by complement deficiency
  • hereditary angioneurotic edema (HAE)
  • the edema in HAE is caused by this deficiency, as the enzyme inactivates cleaving of kininogen to bradykinin; build up of bradykinin is causing of edema
A

C1-inhibitor (C1-INH) deficiency

32
Q

What are the diagnostic tests for meningitis?

A

blood cultures (bacterial growth), imaging (CT or MRI of the head), lumbar puncture

33
Q

What would the CSF from a lumbar puncture show in the case of meningitis infection?

A
  • low glucose level
  • increased WBC count
  • increased protein
  • PCR would be needed to determine presence of pathogen, testing needed for presence of anti-viral antibodies
34
Q

What are the most common causes of meningitis?

A
  • viral infections
  • bacterial infections: pnemococcus (most common for bacteria) and meningococcus (highly contageous, teenagers and YAs, the one that causes local epidemics)
35
Q

How should you (the physician) proceed with treatment in a suspected meningitis case?

A

start empiric antimicrobial therapy aka IV antibiotics Ceftriaxone and Vancomycin (until more specific results can be obtained, bacterial infections tend to worsen without tx)

36
Q

What are the warning signs of immunodeficiency disorder? (8)

A
  • eight+ ear infections in 1 year
  • 2+ serious sinus infections in 1 year
  • 2+ bouts of pneumonia in 1 year
  • 2+ deep-seated infections, or infections in unusual areas
  • recurrent deep skin or organ abscesses
  • need for IV antibiotic therapy to clear infection
  • infections with unusual or opportunistic organisms
  • family history of primary immunodeficiency
37
Q

How do you clinically test classical, alternative, and terminal (MAC complex) pathways of the complement system?

A
  • CH50 test: amount of patient’s serum that will lyse 50% of sheep RBCs coated WITH antibody (tests classical and terminal components)
  • AH50: same as CH50 except sheep RBCs are WITHOUT antibody (tests alternative and terminal components)
38
Q
  • deficiency in complement system
  • rare, hereditary genetic condition that is life threatening
  • sx: edema in various body parts, hands, feet, face, airway; abd pain, nausea, vomiting (caused by intestinal wall swelling)
  • airway edema can cause death by asphyxiation
  • defect in gene that encodes for protein C1-inhibitor (C1-INH)
A

hereditary angioedema (HAE) or C1 inhibitor deficiency

39
Q

What is the cause of swelling in hereditary angioedema (HAE)?

A
  • C1-INH inactivates plasma kallifrein, which is an enzyme that cleaves plasma kininogen to produce bradykinin
  • in HAE, patients have deficiency in C1-INH, thus there is more bradykinin production than normal
  • the bradykinin causes swelling seen in HEA
40
Q

How do you confirm diagnosis of a patient suspected of paroxysmal nocturnal hemoglobinuria (PNH)?

A

test the expression of DAF (CD55) and CD59 on the surface of WBCs by a flow cytometry

41
Q
  • deficiency in complement system
  • failure to regulate formation of MAC
  • somatic mutation causes deficiency of glycosylphosphatidylinositol (GPI)
  • cells lack surface proteins (~40) linked through GPI anchor of cell membranes, most important being DAF (CD55) and CD59 that protect RBCs from complement action
  • sx: intravascular hemolysis, thrombosis, anemia
A

paroxysmal nocturnal hemoglobinuria (PNH)

42
Q

What type of therapeutic antibody would be used for:

  • autoimmune diseases
  • sepsis
  • age-related degenerative diseases
  • transplant rejection, I/R injury
A

complement inhibiting antibodies

(inhibition targets key components of complement cascade: C1, C3, C5, F1, and FD)

43
Q

What type of therapeutic antibody would be used for:

  • viral infections
  • bacterial infections
  • cancer: hematological tumors
  • cancer: solid tumors
A

complement stimulating antibodies

(activation via Fc-induced complement activation (e.g. anti-CD20 for B-cell lymphomas))

44
Q
  • deficiency in compliment system
  • half of all patients have renal disease (most important prognostic factor for poor outcome)
  • renal involvement manifested clinically by hypertension and edema
  • sx: malar erythema (butterfly rash), fatigue, headaches, edema, joint pain
  • lab findings: proteinuria, pyuria, hematuria
A

Systemic lupus erythematosus (SLE)

45
Q

How does the complement system play a role in pathogenesis of glomerular injury?

A
  • production of reactive oxygen intermediates and inflammatory cytokines (C5a) by attracted inflammatory cells
  • production of proteases (when MAC complex forms, it is believed to activate mesangial and epithelial cells to release proteases)
46
Q

What are the 2 mechanisms in immune-mediated vasculitis?

A
  • immune-complex deposition
  • direct antibody interaction

SFM (21 decks)

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