B-program is focused on comprehensive research aimed at elucidating pathogenesis of infections caused by bacterial and viral pathogens. In the bacterial area the research is focused mainly at intracellular pathogen Francisella tularensis. F.tularensis has attracted attention historically as a biological weapon, due to its high infectivity in aerosol, and the severity of disease in humans. There is no licensed vaccine currently available, although an attenuated live vaccine strain (LVS) was identified in the middle of the last century and has been successfully used to protect humans. All the efforts are underway to determine proteins involved in virulence mechanisms of this pathogen focusing on development of functional save and fully characterized vaccine against tularemia disease. Another objective is description of specific response of immunity components required for the Francisella infection, e.g. early response of macrophages after Francisella binding to surface molecules and moreover, role of particular proteins in intracellular fate of Francisella in the macrophages. Projects in the area of viruses pathogenic for humans are aimed at several virus groups. In the area of highly pathogenic viruses that cause hemorrhagic fevers, an ongoing collaborative project is focused on creation of a system for identification of causative agents of hemorrhagic fevers based on real time PCR. With increasing effort we have been focusing on elucidating of effects that some viruseselicit on signal transduction cascades of T lymphocytes. These cascades can be crucially affected by viral pathogens such as measles virus, herpetic viruses, lentiviruses and others employing mechanisms that lead to blunting of the T cell response. Other ongoing studies are focused on molecular epidemiology of Varicella-Zoster virus and also some genetic determinants of innate immune responses, such as the receptors and activation mechanisms of NK cells.