Tissues were prepared as 10% (w/v) homogenates in HBSS supplemented with 10% heat-inactivated (56uC for 30 minutes) fetal bovine serum and antibiotics (200 U/ml penicillin and 50 mg/ml streptomycin). Serum for virus and neutralizing antibody assays was separated from whole blood by centrifugation at 1,500 x g for 15 minutes and stored at -80uC until assayed. Tissue homogenates were similarly clarified by centrifugation, and supernatants were harvested and stored at 280uC until assayed.