Wfdc18, also known as Wdnm1 or Expi, belongs to the 'four-disulphide core' family of proteins and may have proteinase inhibiting capacity [6]. It has been associated with various biological processes, though its exact function is still being explored. Given its potential role as a proteinase inhibitor, it may be involved in processes related to tissue remodeling and cell-matrix interactions.

In sika deer, the WFDC18 gene was abundant at the ossification stage of antler development, indicating its possible role in this process [1]. In mouse mammary gland, WDNM1 (alias of Wfdc18) was predominantly expressed in the layer of secretory epithelial cells surrounding the lumen of mammary gland alveoli, and its expression was down-regulated during involution [4]. Also, in mouse mammary epithelial cells, EGF strongly inhibited the expression of WDNM1 [5]. In mouse models related to liver fibrosis, the extracellular proteinase inhibitor gene Expi (Wfdc18) within a 6 Mb interval on chromosome 11 was ranked as a strong candidate that may modulate the severity of liver fibrosis [2]. In an imiquimod-induced psoriasis model, sakuranetin upregulated Wfdc18, suggesting its role in epidermal homeostasis and skin barrier function [3].

In conclusion, Wfdc18 plays important roles in multiple biological processes such as antler ossification, mammary gland involution, liver fibrosis, and skin barrier function. Studies using mouse models, in particular, have been valuable in revealing these functions, providing insights into its potential significance in diseases related to these processes, including liver fibrosis and psoriasis.