2. Control of the Immune Response

Question 1

once an immune response is initiated, it can be rapidly expanded, therefore for an efficient immune response, __ __ must exist

Answer 1

regulatory mechanisms

Question 2

regulation of immune responses: 2 regulations by antigen

Answer 2

immunity and tolerance

Question 3

regulation of immune responses: 3 major regulators

Answer 3

antigen, antibody, cytokines

Question 4

intrinsic properties and extrinsic factors affect the immunogenicity of proteins

Answer 4

size, dose, route, composition, form, similarity to self protein, adjuvants, interaction with host MHC
- amount of antigen affects immunogenicity response (intermediate dose will increase immunogenicity; high or low dose will decrease immunogenicity)

Question 5

4 ways of regulation by antibody

Answer 5

• antigen blocking
• receptor cross-linking
• passive regulation of antibody affinity
• idiotypic regulation

Question 6

antigen blocking

Answer 6

• competition for antigen with antigen receptor on B cells
• process is dependent on:
  
  • antibody concentration
  • antibody affinity

Question 7

receptor cross-linking

Answer 7

antibody, when bound to antigen, can inhibit B cell differentiation by cross-linking antigen receptors with Fc receptors on B cells

Question 8

passive regulation of Ab affinity

Answer 8

• antibody in low concentrations cannot completely inhibit further antibody production but by sequestering some of the free antigen, it makes it scarce
• only B cells with high affinity receptors for the antigen will bind it
  
  • these cells are the ones that will selectively differentiate and make antibodies of high affinity for the antigen

Question 9

4 properties of cytokines

Answer 9

• pleiotropism
• redundancy
• synergy
• antagonism

Question 10

cytokines in innate immune response

Answer 10

• macrophages, dendritic cells, and NK cells are major producers of TNFalpha, IL-1, IL-6, IL-8, and many chemokines (these are all important intercellular communicators, inducing inflammation, and immune responses)

Question 11

viruses and some bacteria induce IL-12 secretion by dendritic cells that can activate NK cells to produce IFNgamma, what happens next?

Answer 11

naive CD4 T cells, activated in the presence of IL-12 and IFNgamma, are committed to differentiate into Th1 cells

Question 12

other pathogens (e.g. worms) may cause the synthesis and secretion of IL-4 by NKT cells, what happens next?

Answer 12

naive CD4 T cells activated in the presence of IL-4 are committed to differentiate into Th2 cells

Question 13

cytokines in adaptive immune response

Answer 13

• if an adaptive or cell-mediated response develops, T cells (especially CD4+) become a major producer of cytokines
• their effects generally either promote or control further responses and they include IL-2, IL-4, IL-5, IL-10, IL-13, IL-17, IL-22, and TGFbeta (second wave of cytokines)

Question 14

mechanisms of helper T cells mediated activation of B lymphocytes

Answer 14

1. activated helper T cell expresses CD40L, secretes cytokines
2. B cells are activated by CD40 engagement, cytokines
3. B cell proliferation and differentiation

Question 15

costimulatory signals

Answer 15

communicate between two cells

Question 16

depending on the T cell costimulatory molecule and its ligand, you can have __ or __ stimulation

Answer 16

positive or negative

Question 17

idiotype

Answer 17

antigenic constitution of the variable region of an Ig molecule

Question 18

idiotopes

Answer 18

antigenic determinants of which the idiotype is made up

Question 19

paratope

Answer 19

part of the variable region which forms the antigen binding site

Question 20

anti-idiotype

Answer 20

antibody that recognizes idiotypic determinants of other antibodies (reacts to foreign-looking binding site of another Ab)
- anti-idiotypic Ab must have their own idiotypes, and Ab against those idiotypes must also exist (anti-anti-idiotypic Ab) and so on

Question 21

what does Jerne’s proposed idiotype network say about anti-idiotypic antibodies

Answer 21

anti-idiotypic antibodies do exist in circulation but Jerne’s network, while theoretically possible, proved not to play a major role in the regulation of Ab response (unlikely to cause major up/down regulation)

Question 22

major participants of cell network

Answer 22

• macrophages
• lymphocytes (particularly T lymphocytes)
  
  • helper T cells
  • regulatory T cells
  • B cells

Question 23

cellular networks control what?

Answer 23

up/down regulation

Question 24

regulatory T cells (Tregs)

Answer 24

• aka suppressor T cells
• subpopulation of T cells that modulate the immune system
• maintain tolerance to self antigens and prevent autoimmune disease
• immunosuppressive and downregulate the induction and activation of effector T cells
• suppress the immune responses of other cells
• “self-check” for the immune system to prevent excessive reactions
• involved in shutting down responses after they have successfully eliminated invading organisms, and also in preventing autoimmunity

Question 25

T cell precursor cells within the thymus develop into cells with different effector functions

Answer 25

- Tp (T cell precursor starts in thymus) - CD4+ and CD8+ (periphery)

Question 26

CD8+ cytotoxic T cell

Answer 26

- kills infected target cell - participates in macrophage activation - releases perforin and granzymes

Question 27

CD4+ Th1 cell

Answer 27

- produces IFNgamma - promotes cellular activity - participates in macrophage activation

Question 28

CD4+ Th2 cell

Answer 28

- produces IL-4, IL-5, IL-13 - promotes humoral immunity - promotes antiihelminth responses

Question 29

CD4+ Th17 cell

Answer 29

- produces IL-17 - involved in host defense and pathogenesis of autoimmune disease

Question 30

CD4+ Treg cell

Answer 30

- modulates immune response