BHK21 and L929 cells were maintained in Dulbecco's modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 2mM L-glutamine, 1 mM sodium pyruvate, antibiotic-antimycotic solution, and 16 nonessential amino acids (complete DMEM). WNV strain TX 2002-HC (WN-TX) was isolated by as previously described [11] . Working stocks of WN-TX were generated by a single round of amplification on Vero-E6 (ccl-81; ATCC) cells, and supernatants were collected, aliquoted, and stored at 280uC. Virus stocks were titered by a standard plaque assay on BHK21 cells as previously described [40] .