Chagas' disease is a chronic, debilitating and incapacitating illness, caused by the protozoan parasite Trypanosoma cruzi when infective trypomastigotes invade host-cells. Although the mechanism of trypomastigotes interaction with mammalian cells has been intensively studied, the signal transduction mechanisms involved still remain to be elucidated. Our group has previously shown that the conserved FLY domain (VTVXNVFLYNR), present in all members of the gp85/trans-sialidase glycoprotein family, coating the surface of trypomastigotes, binds to cytokeratin 18 (CK18), present on the surface of LLC-MK₂ epithelial cells, and significantly increase parasite entry into mammalian cells [Magdesian et al. (2001) JBC 276:19382-9]. These findings indicated that T. cruzi entry might occur through an active, parasite-driven process with the parasite actively pursuing signal transduction in host cells. In order to characterize the mechanism involved in the FLY domain potentiation of T. cruzi infection, we analyze different signaling cascades in mammalian cells exposed to this domain.  Our data shows that the FLY domain, present on the surface of trypomastigotes or on latex beads binds to CK18 and promotes CK18 dephosphorylation, host cell plasma membrane reorganization and activation of the extracellular signal-regulated kinase (ERK1/2) antiapoptotic signaling cascade, culminating in an increase of approximately 9 fold in the number of parasites/cell. Inhibition of ERK1/2 phosphorylation by U0126 completely blocks the adhesion of FLY domain to cells and blocks by 57% the host cell infection by T. cruzi, indicating that the conserved FLY domain is an important tool that trypomastigotes have evolved to specific exploit the host cell machinery and guarantee a successful infection.