1. Department of Propaedeutics of Internal Diseases, Faculty of Medicine, Medical University—Plovdiv, 4000 Plovdiv, Bulgaria
2. Department of Immunology, The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3. Department of Developmental Biology, Paisii Hilendarski University of Plovdiv, 4000 Plovdiv, Bulgaria
4. Faculty of Medicine, Sofia University “St. Kliment Ohridski”, 1407 Sofia, Bulgaria