1. Department of Paediatrics, County Hospital, Bartók B. 2-27, H-4043 Debrecen
2. Department of Medicine, University Medical School of Debrecen, H-4012 Debrecen
3. Department of Microbiology and Biotechnology, Lajos Kossuth University, PO Box 63, H-4010 Debrecen, Hungary
4. Biochemistry Section, Division of Life Sciences, King's College, Campden Hill Road, London W8 7AH, UK