Differential expression of KLK7 and SOD2 transcripts. A. Detail of the supervised hierarchical grouping based on differentially expressed genes between normal/HPV16-immortalized keratinocytes and HPV 18-immortalized ones, after treatment with TNF for 60 hours. B. Northern blot analysis of KLK7 and SOD2 transcription levels. Arrows indicate the two alternative splicing products of KLK7 in HPV18-immortalized keratinocytes (GenBank # NM_005046); the SOD2 transcript is induced by TNF in both PHK and HPV16-immortalized cells but not in HPV18-immortalized cells (GenBank # NM_00636). A probe against GAPDH was used to monitor comparable loading between samples.