B10.BR mice were immunized with 1610 10 particles of recombinant virus per mouse either by intramuscular injection (50 ml) in the right hindlimb, or by oral gavage (100 ml) using oral feeding needles (18G, 2.25 mm dia., Popper & Sons, Inc, New Hyde Park, NY). For nasal immunization, mice were anesthetized with isoflurane. Once anesthesia was achieved, 1610 10 particles of virus slowly delivered as a bolus into the nostrils using a standard micropipette (Gilson, Middleton, WI) as previously described [39] .