Type 1 IFN receptor subunit 1 deficiency reduces medial elastin degradation and smooth muscle cell depletion in experimental AAAs. Acetone-fixed aortic frozen sections were prepared from wild type (WT, n = 7) and type 1 IFN receptor subunit 1-deficient (IFNAR1−/−, n = 12) mice 2 weeks after elastase infusion and stained using the Verhoeff’s Van Gieson (EVG) procedure and immunostaining for medial elastin and smooth muscle cells (SMCs), respectively. Elastin degradation and SMC depletion were graded as I (mild) to IV (severe). (A) Representative histologic images demonstrate relative medial elastin and SMC preservation in IFNAR1−/− as compared to WT mice. (B,C) Quantification (median and interquartile) of medial elastin and SMC destruction scores between groups. Nonparametric Mann–Whitney test, ** p < 0.01 compared to WT mice. Scale bar: 200 μm.