Since the above studies have shown that SF2/ASF regulates alternative splicing of CD200, we wondered whether expression of SF2/ASF increased in A/J mice post infection. We performed western blotting using anti-SF2/ASF antibody. As shown in Figure 7E , no obvious difference of SF2/ASF level was seen between A/J and C57BL/6J mice before viral infection. Increased expression of SF2/ASF was detected in lungs of A/J mice 12 h postinfection, whereas no increase of SF2/ASF in C57BL/6J mice even 36 h postinfection, suggesting that the role of virus on host CD200 expression is mediated by SF2/ASF.