PDCD1 and infection: This contrasts with data from previous studies of parasitic helminth infections, where a blockade of PD1 during infection with Litomosoides sigmodontis led to a major restoration of Th2 responsiveness mediated by PDL-2 (52), or exposure to adult schistosome worms (prior to the Th2-polarized chronic phase of infection), where T cell anergy was induced via PDL-1-mediated regulation (53).