PTGDS is expressed in the nonpermanent portion of select human hair follicles in haired scalp, and more variably in bald scalp. (A to C) PTGDS immunostaining (brown) with blue nuclear counterstain in normal human hair follicles (A and B) and bald scalp hair follicle (C). (A) A single follicle in haired scalp with staining for PTGDS inferior to the isthmus. (B) Most anagen follicles of haired scalp have little staining for PTGDS. (C) Miniaturized hair follicle with PTGDS staining in sebocytes and hair follicle keratinocytes. Scale bars, 100 μm. (D to F) Immunofluorescence staining for PTGDS (green), nuclei (blue), and either KRT15 (red) (D) or tryptase (red) (E and F) in the hair follicle and adjoining sebaceous gland in bald scalp. Catagen follicle with some PTGDS-positive cells also expressed the mast cell marker tryptase (E). Perifollicular cells show distinct populations of PTGDS- and tryptase-positive cells with overlapping expression (F). Scale bars, 100 μm.