Induction and Monitoring of Active Delayed Type Hypersensitivity (DTH) in Rats

Summary

Delayed type hypersensitivity (DTH) is an inflammatory reaction mediated by CCR7- effector memory T lymphocytes. Here we demonstrate how to induce active DTH in Lewis rats and monitor the inflammatory response.

Abstract

Delayed type hypersensitivity (DTH) is an inflammatory reaction mediated by CCR7- effector memory T lymphocytes that infiltrate the site of injection of an antigen against which the immune system has been primed. The inflammatory reaction is characterized by redness and swelling of the site of antigenic challenge. It is a convenient model to determine the in vivo efficacy of immunosuppressants. Cutaneous DTH can be induced either by adoptive transfer of antigen-specific T lymphocytes or by active immunization with an antigen, and subsequent intradermal challenge with the antigen to induce the inflammatory reaction in a given skin area. DTH responses can be induced to various antigens, for example ovalbumin, tuberculin, tetanus toxoid, or keyhole limpet hemocyanin (KLH).

Here we demonstrate how to induce an active DTH reaction in Lewis rats. We will first prepare a water-in-oil emulsion of KLH, our antigen of interest, in complete Freund's adjuvant and inject this emulsion subcutaneously to rats. This will prime the immune system to develop memory T cells directed to KLH. Seven days later we will challenge the rats intradermally on the back with KLH on one side and with ovalbumin, an irrelevant antigen, on the other side. The inflammatory reaction will be visible 16-72 hours later and the red and swollen area will be measured as an indication of DTH severity.

Protocol

1. Preparation of the emulsion

1. The emulsion is a 1:1 mixture of antigen (DTH can be induced to various antigens: ovalbumin, tetanus toxoid, keyhole limpet hemocyanin....) in aqueous solution added to complete Freund's adjuvant. It is very important to add the antigen to the adjuvant and not the other way round!!!
   
   
2. There is a lot of waste when making and injecting an emulsion, so always prepare 1.5 or 2 times more than what you need.
   
   
3. Dissolve antigen in saline to prepare a 2 mg/ml solution. Do not filter, as you do not want to loose the aggregates!!!
   
   
4. Put complete Freund's adjuvant H37Ra (Difco, catalog # 231131) in a tube and vortex at high speed. Add the antigen drop by drop while vortexing. When all of the antigen is added, vortex for 5 more minutes. The mixture should turn white.
   
   
5. Put the emulsion in a glass syringe and link it to another glass syringe using a 18G bridge (Fisher catalog # 14-825-17L). Send the emulsion from a syringe to the other until it becomes hard (5-10 min). It is best to use two 5 ml syringes. If more than 5 ml of emulsion are required, use several sets of 5 ml syringes.
   
   
6. The emulsion can be stored in the syringes at 4°C for 3 weeks.

2. Immunization of the rats

1. Mix the emulsion in the syringes for a few minutes and transfer to the syringe used for the injection. Inject 200 ml subcutaneously in 1-2 sites at the base of the tail using 23G needles and a Luer-Lok tip 3 ml syringe.

3. Challenge with antigen in the back

1. Seven days after immunization, shave 2 spots on the backs of the rats and inject intradermally 20 ml of a 1 mg/ml antigen solution in one spot and saline (or irrelevant antigen) in the other spot. Do NOT filter the antigen solution, as you may loose aggregates that enhance the inflammatory reaction.
   
   
2. The rats should be anesthesized to avoid movements. Inject the solution intradermally using 27G ½ needles and 1 ml syringes. Change needles between injections.
   
   Note: the challenge can be done in the pinna of the ears instead of the back for more precise measurements. See video at https://www.jove.com/index/Details.stp?ID=325

4. Measurement of DTH

1. The injection site will start turning red and swelling as a sign of inflammation. Measure the diameter of the inflamed area using a ruler or, better yet, a caliper. The maximum swelling should occur between 24 and 72 hours.

Discussion

For a more precise measurement of the DTH reaction we recommend challenging the rats with the antigen in the pinna of the ear. The reaction can then be measured as a difference in ear swelling between the relevant antigen-challenged ear and the ear challenged with either saline alone or with the irrelevant antigen. A demonstration of the challenge in the ear is shown in 1.

Materials

Name	Type	Company	Catalog Number	Comments
Complete Freund’s adjuvant H37Ra	Reagent	Difco Laboratories	231131	Distributed by Fisher under catalog # DF 311-360-5
Keyhole Limpet hemocyanin	Reagent	Sigma-Aldrich	H-5654
Ovalbumin	Reagent	Sigma-Aldrich	A-5503
5 ml glass syringes	Tool	Fisher Scientific	14-823-10 B	Need two 5 ml syringes for each batch of 5 ml of emulsion
18G metal bridge	Tool	Fisher Scientific	14-825-17L
Lewis rats	Animal	Harlan Laboratories		Female rats 7-9 weeks old
23G 1" needles	Tool	Fisher Scientific	14-826 AA	It is best to change needles between rats
3 ml Luer Lock syringes	Tool	Fisher Scientific	05-561-63
DPBS	Reagent	GIBCO, by Life Technologies	14040-182
1 ml regular tip syringes	Tool	Fisher Scientific	22-257-154
27G 1/2" needles	Tool	Fisher Scientific	14-826-48
Electric cordless trimmer	Tool	Braintree Scientific, Inc.	CLP-32130	To shave the rats before antigen challenge in the back.
Use sterile solutions reagents and syringes. The glass syringes and 18G bridges can be autoclaved. Read material data sheet before handling a reagent for the first time and wear appropriate protective equipment.