A sensitive delayed-type hypersensitivity model in the rat for assessing in vivo cell-mediated immunity

Area of Science:

• Immunology
• Toxicology
• Pharmacology

Background:

• Chemicals can alter cell-mediated immunity (CMI), a key immune response.
• Delayed-type hypersensitivity (DTH) assays are crucial for evaluating CMI modulation.
• Standardizing DTH assays is essential for reliable assessment of chemical effects.

Purpose of the Study:

• To identify and optimize a DTH assay for assessing chemically induced CMI changes in rats.
• To establish a reproducible and sensitive method for evaluating immunomodulatory chemicals.

Main Methods:

• Evaluated various DTH assay parameters including antigens, adjuvants, doses, and routes of administration.
• Utilized a footpad swelling reaction in rats, sensitized with bovine serum albumin (BSA) and Freund's complete adjuvant (FCA).
• Measured footpad thickness 24 hours post-challenge and assessed the impact of immunosuppressants like dexamethasone and cyclophosphamide.

Main Results:

• An optimized DTH assay using BSA and FCA in rats demonstrated significant footpad swelling (7-8 mm vs. 3-4 mm).
• The assay showed high reproducibility (CV = 5%) and sensitivity to immunosuppressive drugs.
• Histopathology confirmed a mononuclear cell infiltrate, characteristic of Type IV hypersensitivity.

Conclusions:

• The developed DTH footpad swelling assay is a highly quantitative, sensitive, simple, and reproducible method for assessing chemically induced CMI modulation in rats.
• This model is suitable for toxicological and pharmacological studies investigating immunomodulatory effects of chemicals.