Membranes were blocked for 1 h with 5% dried skim milk in PBS containing 0.1% Tween 20 (T-PBS) and incubated overnight at 4 c with the indicated primary monoclonal or polyclonal (PAb) antibodies against IBV NP (mouse MAb B017; Abeam), mCherry (rabbit PAb; Raybiotech), IBV NS1 (rabbit PAb; kindly provided by Dr. T. Wolff) (Dauber et al„ 2006) or actin (mouse MAb; Sigma).