NF1 and plexiform neurofibroma: Ifnb1 was also slightly down-regulated both in 1-month-old Nf1−/− SCs and 1-month-old Nf+/+ macrophages from Nf1fl/fl;DhhCre mice compared to their wild-type controls, suggesting that levels of IFN-β mRNA might be reduced even in early stages of neurofibroma growth.