PCNA and asthma: The reliability of the identified functional gene clusters is corroborated by manual inspection of well established key genes in asthma, e.g., the inflammation cluster contains lung allergic immune response genes (e.g., cluster 1A: Il4, Il4r, Il13, Il33, Ccl11, Ccl17 and Ccl22; and cluster 1B: Cysltr1, Alox5ap, Arg1, Adam8 and Fcer1g), the lung-specific insult response clusters with known extracellular matrix remodelling, tight junctions, and mucus production genes (e.g., Gstm1, Vegfa, Chi3l1, and Pcna, in cluster 3B, e.g., Pard3, Prkci, and in cluster 3C, e.g., Muc4, Muc5b and Muc5ac).