Chapter 14 - Type IV Allergies

Type IV Hypersensitivities

Cell-mediated (delayed) reactions; Results when T cells respond to antigens displayed on self tissues or transplanted foreign cells; Symptoms arise one to several days following the second contact with antigen

tuberculin reaction (Type IV)

• Acute skin inflammation at the tuberculin extract injection site

• Mainstay diagnostic tool for TB infections

helper T cells, eosinophils

In tuberculin reactions, _______ ___ _______ release cytokines that recruit macrophages, neutrophils, and _________ to the site, causing a red bump

contact dermatitis

Allergen (i.e. poison ivy/oak) penetrates the outer skin layers

contact dermatitis, cytokines

• allergen processed by skin dendritic cells and presented to T cells

• Subsequent exposures attract lymphocytes and macrophages

• Cells release enzymes and ______ that damage epidermis

organ transplantations, graft

• Although it is life-giving, it is plagued with the natural tendency of lymphocytes to seek out and destroy foreign antigens

• The bulk of the damage that occurs in _______ rejections are attributed to cytotoxic T-cell action

MHC classes I and II, genes, foreign

In graft rejection:

• _________ are extremely important for regulating the immune response

• People can exhibit variability in the pattern of these markers, but the pattern is identical in cells of the same person

• Similarity is seen in related siblings and parents, but the more distant the relationship, the less likely that the MHC ______ and markers will be alike

• When a donor tissue (graft) displays varying/different MHC molecules, T cells of the recipient (host) will react to graft as a _______ substance

T cells, antibodies

Host rejection of graft:

• Cytotoxic T cells of host recognize foreign class I MHC markers on grafted cells

• Helper and cytotoxic __ _____ bind grafted tissue and begin rejection process (within 2 weeks)

• ________ formed against the graft contribute to damage

• Result is destruction of vascular supply and death of graft

indigenous

• Some grafted tissues (bone marrow) contain _______ populations of lymphocytes

• Make it possible for graft to reject the host

graft vs host disease

• Graft attacks host tissue bearing foreign MHC markers

• Effects are systemic and toxic

• papular, peeling skin rash is the most common symptom; other organs are also affected

• Occurs within 100 to 300 days of the graft

autograft

transplant from one body site to another on same individual

isograft

tissue from an identical twin is used

allograft

between genetically different individuals of same species; most common graft

xenograft

tissue exchange between individuals of different species