Adoptive transfers. Total donor PECs from uninfected mice (CD45.2) were isolated as described above and resuspended in 300 l of RPMI medium. These cells were injected i.p. into uninfected recipient mice (CD45.1). Recipient mice were rested for 1 h and either left uninfected or infected with LCMV as described above. Staining to identify donor and recipient cell populations was performed as described below using an anti-CD45.1-fluorescein isothiocyanate (FITC) antibody.