1. Department of Experimental Pathology, CINVESTAV-IPN. A. P. 14-740, México 07300, D.F.
2. Program of Molecular Biomedicine, ENMyH-IPN, Fracc. "La Escalera," Ticomán, CP 07320, México, D.F.
3. Department of Experimental Pathology, CINVESTAV-IPN. A. P. 14-740, México 07300, D.F. and Program of Molecular Biomedicine, ENMyH-IPN, Fracc. "La Escalera," Ticomán, CP 07320, México, D.F.