Hypersensitivity type IV

Cell –mediated(Type IV) Hypersensitivity
Learning objectives: At the end of lecture, the students should be able to:
1-Define cell-mediated(type IV) hypersensitivity.
2-Define delayed type hypersensitivity,
3-Describe the morphological features of cell-mediated hypersensitivity.
4-Explain the sequence of celullar events in delayed type hypersensitivity.
5-Discuss types, sources, actions of cytokines in delayed type hypersensitivity.
6-Define T cell-mediated cytotoxicity.
7-Explain the mechanisms of T cell-mediated cytotoxicity.
Cell-mediated (Type IV) hypersensitivity
-Definition.
-Pattern of immunologic response:
1-variety of intracelullar microbiologic agents {such as a bacterium [Mycobacterium tuberculosis], viruses, fungi, protozoa, and parasites.}
2-skin sensitivity to chemical agents.
3-graft rejection.
4-many autoimmune diseases.
Forms of cell-mediated (type IV) hypersensitivity
-Forms:
1-Delayed type hypersensitivity (CD4+helper T lymphocytes.
2-T cell-mediated cytotoxicity (CD8+ T cell)
Delayed type hypersensitivity
-Definition.
-Examples(such as tuberculin reaction)
a protein-lipopolysaccarides component of the tubecle bacillus.
Features of delayed type hypersensitivity
-Morphology:
* At site of reaction reddening and induration.
Dermal edema and deposition of fibrin in interstitium.
*hypertrophy and hyperplasia of endothelial cells.
*Presence of CD4+(helper) T lymphocytes.
*Presence of granuloma and granulomatous inflammation.
Celullar events in delayed type hypersensitivity
-Antigen presenting cells.
-CD4+ T cells.
-TH1 cells----Cytokines secretion.

Cytokines secretion in delayed type hypersensitivity
-Sources.
-Types.
*Interleukine-12 (IL-12).
*Interferon-gamma (IFN- ).
*Interleukine-2 (IL-2).
*Tumor necrosis factors (TNF).
*Chemokines
-Actions.
T cell-mediated cytotoxicity
-Definition.
-Examples.
-The role of cytotoxic T lymphocytes(CTLs) in:
1-elimination of of virus-infected cell.
2-tumor immunity.
Mechanisms of T cell-mediated cytotoxicity
-Mechanisms:
1-Perforine-granzyme-dependent killing.
2-Fas-Fas Ligand-dependent killing.
Questions:
Q1)Describe the histopathological features of granuloma in delayed type hypersensitivity.
Q2)Describe the histopathological features of contact dermititis.
Q3)Discuss the mechanism of perforine-granzyme pathway.
Q4) Discuss the mechanism of fas-fas ligand pathway.
Q5)Explain the roles of cytotokines in pathogenesis of T cell-mediated injury.
* References:
___________
1-MacSween R.N.;and Whaly K.(Murs Textbook of pathology); 13th edition,Arlond.1997.
2-Kumar V.;Abbas A.; and Fausto N.(Robbin and Cortan, Pathologic basis of disease).7th edition. Elsevier Sounder. 2004.
3-Rosal J. (Ackerman s surgical pathology); 9th edition.Mosby.2003.

4-Walts J.B.,Talbot L.c.(general pathology ); 7th edition ,Churchill Livingstone; 1996 .

5-Krishna V.(Text book of pathology );Orient Longman Private