his research was financed by grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP #2007/04870-9 to JCM and #2008/57830-7 to RPMF) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq #304174-2006-8 to JCM and #471933/2008-2 to RPMF). KCSF acknowledges an MS scholarship (CNPq), ROF a PhD scholarship (FAPESP), DCM post-doctoral scholarships (FAPESP and CNPq), and JCM and RPMF research scholarships (CNPq). We thank Nilton Rosa Alves and Susie Keiko Teixeira for technical assistance; we are most grateful to Dr FA Leone, who kindly provided access to laboratory facilities.