To evaluate this hypothesis we plan to enroll between 100 - 300 patients over the course of 2 years from both countries. Blood samples before and at predetermined time points after the application of Purified Protein Derivative (PPD) will be obtained to determine the fraction of CD4+ T cells which produce interferon gamma in response to stimulation with PPD with a 16hr antigen stimulation assay. Appropriate staining will be done to ascertain the phenotype as well as cytokine production (Interferon gamma, ( IFN gamma), Interleukin 2 (IL2) and Tumour Necrosis Factor (TNF)). Additionally lymphocyte proliferation will be studied using 5-(and-6)-carboxyflouorescein diacetate succinimidyl ester (CFSE.)