CCL28 and xerostomia: In contrast, a study by Yu et al. showed significantly increased CCL28 mRNA expression in the PG of the xerostomia group compared with that in the healthy control group, whereas CCL28 mRNA expression was significantly decreased in the PG of the patient with SS group compared with that in the healthy control group [49], implying that the effect of CCL28 on the PG, primarily composed of serous glands, under physiological conditions, remains unknown.