1. Departamento de Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, México D.F., C.P. 02200 México
2. Centre for Human Immunology, Department of Microbiology and Immunology, University of Western Ontario, London, ON N6A 5C1, Canada
3. Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Alexandria University, Alexandria, Egypt