Innate Immunity

Question 1

Big picture of Complement

Answer 1

OIL:
Opsonization
Inflammation
Lysis

Question 2

Complement pathways

Answer 2

1. Alternative
2. Lectin
3. Classic

Question 3

First complement pathway to be activated?

Answer 3

Alternative

Question 4

Alternative pathway steps

Answer 4

1. C3 cleaved –> C3a & C3b
2. C3b can bind microbe (or be inactivated)
3. C3b forms C3 convertase (C3bBb)
4. C3 convertase continues to convert C3 –> C3a & C3b
5. C3b either:
   a - acts as opsonin
   b - forms C5 convertase (C3bBb5b)
6. C5 convertase converts C5 –> C5a & C5b
7. C5b + C6-9) form membrane attack complex (MAC), which causes lysis

Question 5

Lectin pathway steps

Answer 5

1. MBP cleaves:
   a. C4 –> C4a & C4b
   b. C2 –> C2a & C2b
2. C4b + C3b form C3 convertase (C4b2b)

same as 4-7 for alternative pathway

Question 6

Classical pathway steps

Answer 6

Requires antibodies (IgM & IgG)

1. Ab bind bacteria, C1 binds Ab at another site
2. Conformational change in C1, cleaves C2 & C4

follows the rest of the lectin pathway

Question 7

Classical pathway starting points/trigger

Answer 7

C1qrs, C2, and C4

Fc portion of Ab (IgM, G1, G2, G3) or CRP with C1q

Question 8

Lectin pathway starting points

Answer 8

Plasma-derived mannose-binding lectin/ MBL, C2 & C4

Question 9

Alternative pathway starting points

Answer 9

C3, factor B, D, and properdin

Question 10

What is opsonization?

Answer 10

Coating of pathogen with molecule that enhances phagocytosis by fixation of opsonins (C3b) on pathogen surfaces

Question 11

Anaphylatoxins and function

Answer 11

C3a, C4a, C5a, increase vascular permeability

Question 12

Chemoattractants and function

Answer 12

C3a and C5a, attract neutrophils and monocytes

Question 13

MAC components and function

Answer 13

Membrane attack complex: C5b-C9

Creates perforations in cell membranes –> lysis

Question 14

What recognizes C3b?

Answer 14

Complement receptor 1 (CR1)

Question 15

MAC-induced lysis limitations

Answer 15

Only effective against microbes with thin cell walls, Neisseria species

Question 16

Complement regulation: C3 convertase

Answer 16

down-regulated by decay-accelerating factor (DAF); displaces Bb from C3b

Question 17

DAF deficiency

Answer 17

Uncontrolled complement activation –> RBC lysis, paroxysmal nocturnal hemoglobinuria (PNH)

Question 18

Complement regulation: C1

Answer 18

C1-inhibitor: protease inhibitor that down-regulates C1r/s activation

Question 19

C1-inhibitor deficiency

Answer 19

excessive vasoactive peptides (bradykinins) –> hereditary angiodema

Question 20

C1, C2, C4 deficiency

Answer 20

Increased risk of immune complex disease (SLE)

Question 21

C3 deficiency

Answer 21

Increased risk of encapsulated bacteria infection (pyogenic infections)

Question 22

C5b-C9 deficiency

Answer 22

Increased susceptability to Neisseria infections (gonorrhoeae or meningitidis)

Question 23

Neisseria meningitidis

Answer 23

Gram (-) cocci
Produces polysacc capsule
Fever + petechial rash + hypotension

Question 24

The physiological role of innate immunity

Answer 24

To protect the host during the time between microbial exposure and adaptive immunity responses

Question 25

Neturophil (Cell type and function)

Answer 25

WBC granulocyte

Function: engulf bacteria/fungi; oxidative burst

Question 26

Monocyte/

Macrophage (Cell type and function)

Answer 26

WBC Mononuclear

Function: engulf bacteria, fungi, and cellular debris; produce cytokines; antigen processing

Question 27

Eosinophil (Cell type and function)

Answer 27

WBC granulocyte

Function: Associated with allergic response and parasitic infection

Question 28

Basophil (Cell type and function)

Answer 28

WBC granulocyte

Function: Associated with hypersensitivity and release histamine

Question 29

Mast Cell (Cell type and function)

Answer 29

Bone marrow derived

Function: Granules contain vasoactive amines like histamine, proteases kill bacteria

Question 30

Natural Killer (NK) (Cell type and function)

Answer 30

WBC Lymphocyte

Function: Recognizes stressed or infected cells and kills by secreting macrophage-activating cytokine INF-gamma

Question 31

Dendritic Cell (Cell type and function)

Answer 31

Bone marrow derived

Function: Phagocytosis, Antigen-presenting cell, Initiation of T-cell responses