The CXCL17 gene is located on the long arm of chromosome 19, and it spans about 15 kb and includes four exons.

Expression of the CXCL17 gene has been observed in several tissues. In human tissues, Northern blot analysis showed that CXCL17 is expressed in the trachea, stomach, lung, skeletal muscle, and the fetal lung (Pisabarro et al., 2006; Weinstein et al., 2006). No Northern blotting signal is detected from the brain, heart, colon, thymus, spleen, kidney, liver, small intestine, placenta, and peripheral blood lymphocytes (Weinstein et al., 2006). Furthermore, investigation of CXCL17 expression using a comprehensive human gene expression microarray database showed that expression is restricted to mucosal sites including the digestive system, lung airways, the urethra, and several sites of the female reproductive system (Burkhardt et al., 2012).
In mouse tissues, CXCL17 is expressed in the lung, thyroid, submaxillary gland, epididymis and uterus, with faint signals in the ovary and prostate (Weinstein et al., 2006).
In rat tissues, real-time PCR using 22 different rat tissues demonstrated that CXCL17 was expressed mainly in the stomach, duodenum, lung, and salivary gland (Lee et al., 2013).

Extensive analyses of CXCL17-secreting or -producing cells have yet to be performed. Some reports have demonstrated CXCL17 expression by immunostaining. Immunohistochemistry of the normal lung in adult humans demonstrated that CXCL17 was constitutively expressed on the bronchial and bronchiolar epithelium. Additionally, CXCL17 expression was also observed in the normal small intestine (duodenum) and colon. Specifically, CXCL17 production was localized to the villus and some crypt epithelial cells of the small intestine and colonic epithelial cells (Pisabarro et al., 2006). In mucosal tissues of the gastrointestinal tract, distinct cells were found that exhibited CXCL17-positivity with unique cell surface markers and morphological characteristics, and these cells were identified as CD68⁺ macrophages and CD138⁺ plasma cells.

Chemokines are generally classified into one of four groups on the basis of protein structure (cysteine residues), and can also be classified on the basis of functional differences (Zlotnik and Yoshie, 2012). Chemokine groups based on functional characteristics include inflammatory, homeostatic, dual-function, plasma or precursor, and platelet chemokines. However, the functional and physiological role of CXCL17 remains unclear and has yet to be categorized.
Interestingly, C-X-C chemokines are divided into two types on the basis of angiogenic potential: pro-angiogenic types with an ELR motif and angiostatic types with a non-ELR motif. The ELR motif consists of the tripeptide glutamate (E)-leucine (L)-arginine (R). Pro-angiogenic types with an ELR motif which attract neutrophils are referred to as ELR⁺ chemokines, while angiostatic types that preferentially attract lymphocytes are referred to as ELR^- chemokines (Vandercappellen et al., 2008; Strieter et al., 2005). In the case of CXCL17, the presence of the ELR motif has yet to be confirmed. However, CXCL17 can be functionally classified as an ELR⁺ chemokine since CXCL17 shows pro-angiogenic function and neutrophil migration (Weinstein et al., 2006; Vandercappellen et al., 2008; Zlotnik and Yoshie, 2012).
Although the function and role of CXCL17 has been extensively investigated, its main receptor has yet to be identified.