KRT15 and hydrops fetalis: Even though our microarray analysis had not identified any HF-associated keratins as spermidine-regulated genes (possibly for methodological or sub-threshold reasons), quantitative immunohistomorphometry of K15 expression in situ clearly showed that spermidine significantly increased K15 immunoreactivity in the basal layer of the proximal ORS after 6 days (Figure 4A).