Type IV Hypersensitivity Reactions

Question 1

what is type IV known as

Answer 1

delayed type hypersensitivity reaction (DTH)

Question 2

what cell type does type IV involve?

Answer 2

antigen-specific Th1 cells

Question 3

what is the reason for the damage that IV causes?

Answer 3

damage of host tissues comes from activity of antigen-nonspecific immune cells, responding to cytokines and chemokines that were secreted from the activated Ag-specific T cells, CD8 cells can be involved

Question 4

steps of IV reaction

Answer 4

1. activation of Ag-specific Th1 and Th17 cells in a PREVIOUSLY SENSITIZED PERSON
2. production of proinflammatory cytokines by Ag-specific T cells
3. recruitment and activation of Ag-nonspecific inflammatory leukocytes

Question 5

timing of type IV reactions?

Answer 5

1. sensitization stage

2. elicitation stage

Question 6

how long does the sensitization stage take?

Answer 6

BEFORE type IV occurs takes about 1-2 weeks

Question 7

how long does the elicitation stage take?

Answer 7

THE ACTUAL TYPE IV REACTION, takes 48-72 hours

Question 8

what is the effector stage of DTH?

Answer 8

Th1 memory cells are activated and produce cytokines

Question 9

what cytokines cause tissue destruction and inflammation in the effector stage of DTH?

Answer 9

IFN-gamma
TNF-alpha
TNF-beta

Question 10

what does IL-2 do in the effector stage?

Answer 10

activates T cells and CTLs

Question 11

what do chemokines do in the effector stage?

Answer 11

facilitated macrophage recruitment

Question 12

what cytokines increase local granulocyte and macrophage proliferation in the effector stage?

Answer 12

IL-3 and GM-CSF

Question 13

what occurs during the effector stage of DTH?

Answer 13

inflamed area becomes red and fluid filled
the tissue damage activates clotting cascades and tissue repair, and the continued exposure to Ag causes chronic injury and repair = granuloma formation

Question 14

what does IFN gamma do during DTH

Answer 14

1. induces expression of vascular adhesion molecules

2. activates macrophages, increasing release of inflammatory mediators

Question 15

what do TNFalpha and beta do during DTH?

Answer 15

1. cause local tissue destruction

2. increase expression of adhesion molecules on local blood vessels

Question 16

what do IL-3 and GM/CSF do during DTH?

Answer 16

stimulate monocyte production by bone marrow stem cells

Question 17

what causes contact dermatitis

Answer 17

lipophilic compounds penetrate the skin and attach to carrier molecules on cells

Question 18

what substances commonly cause contact dermatitis?

Answer 18

2,4-dinitrochlorobenzene (DNCB)
nickel, chromium
poison ivy, poison oak

Question 19

how do granulomas form?

Answer 19

ag is resistant to elimination and keeps attracting macrophages, giant cells form and in 21-28 days, granulomas form.

Question 20

TB skin test is caused by what?

Answer 20

cutaneous inflammatory reactions by type IV. 48-72 hours after challenge with tuberculin Ag.

Question 21

what is GVHD

Answer 21

graft vs host disease, where transplanted immune cells recognize the host (recipient) cells as foreign, T CELL MEDIATED DISEASE

Question 22

3 phases of GVHD

Answer 22

1. conditioning regimen damages and activates host tissues to secrete cytokines that upregulate MHC Ag
2. donor T cell activation
3. multiple inflammatory cascades (th1 CD4–>TNFa, IL-1__>apoptosis)