Ch. 8 Humoral elimination of extracellular microbes and toxins

Question 1

IgG effector function

Answer 1

• neutralize microbes by binding to them and blocking their funct.
• opsonize for phagocytosis
• activate classical complement pathway
• antibody dependent cytotoxicity by NK cells (ADCC)
• neonatal immunity - transfer across placenta
• feedback inhibition to turn off response when antigen/antibody complex binds back to B-cells

Question 2

IgA effector function

Answer 2

• mucosal immunity - only one that can cross mucosa
• secreted into lumens of gastrointestinal and respiratory tracts
• ## neutralizes antibodies

Question 3

IgM

Answer 3

Pentimer - activates classical pathway of complement

- first antibody

Question 4

IgE effector Function

Answer 4

• Antibody-depend. cytotoxicity by eosinophils (ADCC)

- mast cell degranulation - immediate hypersensitivity reactions

Question 5

FcR receptors on which cells

Answer 5

• B-cells - antibody feedback inhibition (IgG)
• Macrophages, neutrophils - phagocytosis (IgG)
• NK cells - Antidbody dependent cellular cytotoxicity (ADCC) - (IgG)
• Eosinophils and Mast cells - (IgE)

Question 6

Main Effector Functions of antibodies

Answer 6

• Neutralize microbe
• opsonization and phagocytosis
• ADCC with NK cells
• ADCC with eosinophils
• activation of the complement system

Question 7

4 broad steps to activation of complement in all three pathways

Answer 7

• Binding of C proteins to microbe/antibody on microbe
• Formation of C3 convertase
• cleavage of C3
• Formation of C5 convertase

Question 8

Alternative Pathway

Answer 8

• C3->C3a C3b
• C3b stabilized on microbes
• Factor B cleaved by D
• C3bBb -> C3 converstase
• C3bBb3b -> C5 convertase

Question 9

Classical

Answer 9

• C1q binds Fc IgM or IgG
• C1r/s cleaves C4
• C4b and C1 cleave C2
• C4bC2a-> C3 convertase
• C4bC2aC3b -> C5 convertase

Question 10

Lectin Pathway

Answer 10

• MBL binds mannose on microbe
• MBL Cleaves C4
• MBL/C4 cleaves C2
• C4b2a -> C3 convertase
• C4b2a3b -> C5 convertase

Question 11

Late steps of complement pathway

Answer 11

• C5b recruits C6, C7, C8
• These form a complex and recruit C9 which forms a pore and lyses the microbe
• Membrane attack complex - MAC

Question 12

Functions of complement system

Answer 12

• Most important - opsonization and phagocytosis - C3b binds to microbe. Type 1 receptor (CR1) on macrophages and neutrophils recognize C3b and phagocytose
• Activation of immune system - C3a, C4a, C5a stimulate leukocytes and attract them - act on endothelial cells
• Complement- mediated cytolysis - late steps lead to Membrane Attack Complex
• Stimulate humoral immunity - when antigens bind to BCR on B-cells there needs to be a second signal to activate B-cells. C3d binds to a CR2 on the b-cells to give this second signal

Question 13

Inhibition of complement

Answer 13

• DAF - blocks formation of C3/5 convertase (blocks C3bBb, blocks C4bC2a binding to C3b)
• MCP - helps Factor I break down C3b to inactive forms
• C1 inhibitor
• Factor H - dissociation of C3 convertase in alternative, co-factor for Factor I

Question 14

mucosal immunity

Answer 14

• IgA production induced at mucosa by TGF-beta
• B1 cells also make it at mucosa
• Poly-Ig receptors are special Fc R that endocytose IgA into endothelial cells and release them into the lumen

Question 15

Neonatal immunity

Answer 15

• Passive immunity

- IgG is passed across placenta and then across intestines from milk by neonatal Fc receptors (FcRn)