Immuno exam 1 - Dr. Quan

Question 1

. Basic Complement functions

Answer 1

• Control of inflammatory reactions
• Chemotaxis
• Clearance of immune complexes
• Cellular activation
• Antimicrobial defense
• **opsonization and cell activation
• **chemotaxis→site of infection
• **lysis of target cells

Question 2

Complement activation pathways

Answer 2

• proenzymes with AS masked→activation with proteolysis cleavage→causes exposure of AS→functions!
• Opsonization function: generates active complement fragments that attach to bactiera→bind to CR receptors on phagocytes→phagocytosis
• Complement-mediated chemotaxis function: microbial surface stimulate activation of complements (C3b→microbe→release of C3a and C5a) →fragments coat microbes and induce chemotaxis →leukocytes kill invading microbes
• Complement-mediated cytolysis function: act of complement system leads to formation of membrane attack complex (MAC)→lysis of microbe
Complement pathway activators: IgM, IgG, lectin

Question 3

• Summary alternative pathway:

Answer 3

o Spontaneous cleavage of C3 generate C3a, C3b
o C3b in fluid deactivated by hydrolysis
o C3b covalently binds to cell surface
o Self surface bound C3b binds to factor H
o C3bH deactivated by factor I
o C3b bound to the surface of microbes binds to factor B
o C3bB cleaved by factor D to generate C3bBb
o C3bBb is the alternative pathway C3 converatse
o C3bBb catalyze significant amount of C3 cleavage
o …..want: C5b

Question 4

• Summary of classical pathway:

Answer 4

o Activated C1 cleave C2 and C4 to form C4b2a
o C4b2a is the classical C3 convertase
o C4b2a3b is the classical C5 convertase

Question 5

C3 convertase

Answer 5

• Necessary in innate immunity as a part of complement system which eventuate in the opsonization of particles, release of inflammatory peptides, C5 convertase formation, and cell lysis.
• C3 convertase cleaves only C3, central molecule of complement system.

Question 6

complement chemotactic factors

Answer 6

• C3b, C3a, C5a

Question 7

opsonins

Answer 7

• Tags placed on microbes to be bale to be phagocytosed
• Macromolecules attached to the surface of a microbe and can be recognized by neutrophils and macrophages
• IgG
• Complement factor C3

Question 8

Fc receptors

Answer 8

• Found on phagocyte
• Fab region of IgG receptor reacts with organism
• Fc RI—high affinity binding
• Fc RII—low affinity binding
• Fc RIII—intermediate affinity binding

Question 9

CD16 function

Answer 9

•	Intermediate binding Fc RIII receptor 
•	RIIIB for neutrophils only
•	RIIIA for NK and Macrophages only 
•	Loss of CD 16 is a signal for macrophages to phagocytose the neutrophils—a signal that they are apoptotic
o	Displays death sign

Question 10

. The killing mechanisms for phagocytosis

Answer 10

• Phagocytosis, cytokine production, granules
• Oxidative mechanisms via phagolysosome
• Non-oxidative via granules and enzymes

Question 11

9. Function of opsonization?

Answer 11

• Opsonization: the process of attaching opsonins, such as IgG or complement fragments, to microbial surfaces to target the microbs for phagocytosis
• Microbs need to be tagged with osonins or they will not be phagpcytosed
• Primary opsonins: IgG (Ag first binds to IgG then binds to phagocyte Fc receptors) And complement factor C3 (which binds to microbe then is bound to C3b receptor on phagocyte)

Question 12

antibody isotypes

Answer 12

• IgG: major Ig in serum; neonatal immunity
• IgD: B cell surfaces
• IgE: found on basophils and mast cells; kills large parastites; contributes to allergic rxn
• IgA: secreted into saliva
• IgM: B cell receptor; first secreted Ab in response to initial antigenic challenge

Question 13

genes controlling Ig expression

Answer 13

• Light chain
o VL: gamma on chromosome 22
o CL: kappa on chromosome 2
• Heavy chain: CH2/CH3 on chromosome 14

Question 14

Ig genes in mature B cells

Answer 14

• V, J, C

* All have to be cut specifically to contribute to diversity

Question 15

• Mechanism 1:

Answer 15

o Germ line DNA: DNA which is passed down through the gametes before it is modified by somatic recombination or maturation
o Pro-B cells (bone marrow stem cells) contain germ line DNA.
o The gene loci for Ig production in Pro-B cells are non-functional due to the lack of open reading frame

Question 16

• Mechanism 2:

Answer 16

o Production of kappa chain protein (CL)
-Germ line DNA for k Chain production is made up by three different gene units: Vk, Jk, and Ck. The presence of complete VkJkCk is not productive.
o There are about 30 Vk segments, 5 Jk segments and 1 Ck unit
o B cell DNA contains rearranged germ line DNA with selected V, J segments
o After deleting intron, B cell mRNA contains a complete open reading frame that consists of VxJyCk
o Constant region is encoded by Ck gene
o Variable region is encoded by VxJy
o The variability of k chain by recombination is 30 x 5 = 150

Question 17

• Mechanism 3:

Answer 17

Production of gamma chain (VL)
-Germ line DNA for 1 Chainproduction is made up by three different gene units: Vl, Jl, and Cl. The presence of complete VlJlCl is not productive.
o There are 30 Vl segments, 7 Jl segments combined with 7 Cl unit
o B cell DNA contains rearranged germ line DNA with selected V, J segments
o After deleting intron, B cell mRNA contains a complete open reading frame that consists of VxJyCy
o Constant region is encoded by Cl gene
o Variable region is encoded by VxJy
o The variability of l chain by recombination is 30 x 7 = 210

Question 18

• Mechanism 4

Answer 18

Production of heavy chain

Question 19

• Mechanism 5:

Answer 19

o Recombinational inaccuracy
o Instead of end to end joining, a few nucleotides can be cut during recombination
o This is not precise

Question 20

• Mechanism 6:

Answer 20

o N-nucleotide addition

o A few nucleotides may be inserted between D and JH and between VH and D to create further diversity

Question 21

• Mechanism 7:

Answer 21

o After antigen stimulation, the V, D, J genes in B cells can make single base changes
o Somatic mutation→increases affinity of antibody

Question 22

• Mechanism 8:

Answer 22

o Class switching

o Alternative splicing produce IgD and IgM

Question 23

SUMMARY of MECHANISMS

Answer 23

• Multiple germ line V genes
• V-J and V-D-J recombinations
• Recombination inaccuracies
• N-nucleotide addition
• Somatic mutation
• Assorted heavy and light chain combination
• Class switching

Question 24

. MAC components

Answer 24

• Complement-mediated cytolysis function: act of complement system leads to formation of membrane attack complex (MAC)→lysis of microbe

Question 25

T cells maturation mechanisms

Answer 25

• Low affinity recognition of peptide/MHC complex on epi cell→ single positive and rescued from programmed cell death
• Failure to recognize peptide-MHC complex on epi cell→apoptosis
• High affinity recognition of peptide-MHC compexes on APCs→apoptosis