SERPINH1 and infection: Upon infecting fibroblasts with the HSP47 lentivirus, a PCR product derived from spliced XBP1 (XBP1-s) mRNA, spliced from unspliced XBP1 (XBP1-u) mRNA, was detected, while infection of the vector virus did not yield a PCR product derived of XBP1-s mRNA (Figure 4A).