Dear Thanu. You need to be a bit more specific in terms what you want to know. For example, PPD can be readily used to stimulate IFN-gamma release in the whole blood assay to test for TB reactivity, and we have used it as an Ag in DC-CD4 T cell assays. If you check in PubMed the articles related to bovine TB, and generating a new vaccine for bovine TB, there are a number of publications in which PPD is used. Does that help for the start? Feel free to ask details directly

The tuberculosis skin test is also known as the tuberculin test or PPD test.The PPD test is used to determine if someone has developed an immune response to the bacterium that causes tuberculosis (TB). It induces interferon synthesis and release from mast cells and active skin cells or melaocytes, it makes third line of defense.The standard recommended tuberculin test is the Mantoux test, which is administered by injecting a 0.1 mL volume containing 5 TU (tuberculin units) PPD into the top layers of skin of the forearm.Skin tests should be read 48-72 hours after the injection. The basis of the reading of the skin test is the presence or absence and the amount of induration (localized swelling).A negative test does not always mean that a person is free of tuberculosis.

Thanu, if you use PPD in a DC-Tc (CD4) assay, you can stimulate them to proliferate and secrete IFNg. The response you get is dependent on timing (as in pulsing of APC with PPD), the dose, cell numbers (on both sides) etc. 

Thank you both for your answers. we're looking at T-ceel proliferation induced by cultured DCs and Macrophages in th epresence of an effective antigen and we decided to use PPD. As we've not worked with PPD before, we weren't sure of the recommended concentration to use and the time of incubation. Dirk Werling, I've noticed that these conditions varies and weren't consistent throughout the literature but most of all no one really explained the priniciples of actions of PPD. However, thanks for your input, we ahve an idea of where/how to begin.

The principle of using ppd is as follows:

The ppd when inoculated is identified by the memory T cells in an individual who is already exposed to TB. These memory cells get activated and send out signal (chemotaxis)to other cells for recruitment to the site of inoculation. There is also release of migration inhibition factors that lead to accumulation and later prolonged deployment of cells. It take something about 24-48 hours for the development of swelling. 

For detail you may see the delayed type hypersensitivity reaction.