This manuscript was reviewed by a professional science editor and by a native English-speaking copy editor to improve readability. We gratefully acknowledge funding from FAPESP-BIOEN (08/52074-0) and CNPq (308197/2010-0) to MAVS. EAOC (12/21064-4), GMQC (08/58243-8) and AVP (12/02671-7) are supported by FAPESP fellowships. EAOC; GMQC and AVP designed and performed the experiments. EAOC and MAVS analyzed the data and wrote the manuscript.