N-NS4B/WARF4 expression is restricted to WNV lineage I. Panel A shows the reactivity of WNV lineage I with MAb3A12 (lane 3), no reactivity was observed in WNV lineage II (lane 4), VERO cells were used as negative control (lane 2). To monitor the infection of VERO cells with both lineage I and II, the membrane was reprobed with a commercial antibody anti-M (panel B). The M protein and other immature forms were detected in both the WNV lineage I and II (lanes 3 and 4). His-WARF4 and His-preM/M proteins were used as positive controls.