Technotes

Technotes

Delayed Type Hypersensitivity

Introduction

Delayed type hypersensitivity (DTH), also known as cell mediated immune memory response or type IV hypersensitivity is characterized by erythema and induration at the site of contact in 

sensitized humans or animals. It is involved in the pathogenesis of many infectious diseases (tuberculosis, leprosy, blastomycosis, histoplasmosis, toxoplasmosis, leishmaniasis, etc.), autoimmune diseases and granuloma due to infection of foreign antigens. Another form of DTH is the contact dermatitis caused by poisonivy,chemicals or heavy metals, etc. Systemic injection of an antigen in an animal results in fever, synthesis of acute phase proteins and death in some instances. The histology of DTH can be diff erent for diff erent species, but in general it is characterized with an infl ux of immune cells at the site of injection, either macrophages and basophils in human and mice or neutrophils in guinea pigs and induration which becomes apparent within 24-72 hours. T cells (either CD4+ or CD8+ depending on the antigen) are required to initiate the reaction even though they make up only a small fraction (10-20%) of the infl ammatory infi ltrates. Cytokines secreted by helper T cells (monocyte chemotactic factor, interleukin-2, interferon γ, TNFα/β) represent the early hallmarks of the infl ammation. However, it remains unclear whether the recruitment of other immune cells to the site of challenge is directly regulated by T cells.



PharmaLegacy Models and Research Tools


DTH Rodent Models:

Dinitrofl uorobenzene (DNFB) induced DTH in ICR, Swiss, or BALB/c mice (Related to contact           dermatitis in human)

* Oxazolone induced DTH in ICR, Swiss, or BALB/c mice (Related to contact dermatitis in human)       

* Methylated bovine serum albumin (mBSA) induced DTH in C57BL6 mice or SD rats (Related to chronic transplant rejection and multiple sclerosis in human. Sheep red blood cells (SRBC) induced DTH in Swiss mice (Related chronic transplant rejection in human.)

Rodent model characteristics:

* Peak response at 24-48h, rare erythema and diff erent numbers of lymphocytes/monocytes across diff erent models       

* High throughput and requirement for smaller quantity of compound

* Low variability between subjects using inbred animals

* Higher concentration of antigen/hapten for induction in certain strains    

Measurement of infl ammatory responses and molecular pharmacology:

* Ear/paw swelling

* Myeloperoxidase assay (neutrophils and granulocytes)

* Cytokine production: TNFα, interferon γ, IL-1β, IL-4, IL-6, Cox-2, (ELISA or Q-PCR)

Histopathology:

* H&E staining: induration and infi ltrations

* Immunohistochemistry: specifi c T cell response and cell proliferation