1. Institute of Microbiology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
2. Immunology Research Group, Hungarian Academy of Sciences, 1053 Budapest, Hungary.
3. National Reference Laboratory of Immunology, National Center of Infectious and Parasitic Diseases, 1000 Sofia, Bulgaria.
4. Department of Immunology, Eötvös Loránd University, 1053 Budapest, Hungary.