Immunosuppressed patients latently infected with TB are at higher risk of developing active TB than patients with normal immune functions. Especially two patient categories are at risk: HIV positives and patients receiving TNF-a blocking medication. Existing methods of diagnosis and surveillance of latent TB infection can not identify who will develop active TB and who can control the infection. There is a need for better understanding of TB specific immune functions,as we believe deficient TB specific immune reactions is a key in reactivation of latent TB infection.