CD99 Is Strongly Expressed in Basal Cells of the Normal Adult Epidermis and Some Subpopulations of Appendages: Comparison with Developing Fetal Skin

Abstract

BackgroundCD99 is a cell surface transmembrane glycoprotein expressed in various tissues. CD99 is differentially expressed between subpopulations of each tissue and is highly expressed in certain hematopoietic and precursor cells. However, there has been no comprehensive study of CD99 expression in normal skin. We evaluated CD99 expression in normal human skin and developing fetal skin. MethodsSeventy-five adult skin samples containing normal skin and eight fetal skin samples of different gestational ages were collected. CD99 immunohistochemical staining was performed to evaluate expression pattern in adult and fetal skin samples. CD99 and CD34 expression were compared by double immunofluorescence. ResultsIn normal adult skin, CD99 was strongly expressed in the membrane of epidermal basal keratinocytes, hair follicle bulges and outer root sheaths, and inner secretory cells of eccrine sweat glands. In fetal skin, CD99 was not expressed on the periderm at 16 weeks of gestation but was expressed in basal cells of fetal skin at around 19 weeks of gestation. CD99 expression became comparable to that of the adult skin after 20 weeks of gestation. CD99 and CD34 were co-expressed in hair follicle outer root sheaths, as seen by double immunofluorescence study. ConclusionsThis is the first study examining CD99 expression pattern in normal adult and fetal skin. CD99 tends to be expressed in the basal/precursor cells of epidermis and in hair follicles. These results provide a basis for future investigation on functions of CD99 in the skin and provide a novel potential target for the treatment of dermatologic lesions.

Wnt-mediated interactions of tumor-initiating cells with a macrophage niche drive skin tumor formation

“…In healthy skin, CD99 expression was nearly absent compared to tumors (Fig. 5F), but in agreement with prior findings 52 , it was expressed in basal epidermal cells, suggesting a link with cell proliferation capacity. In culture, CD99 was also highly expressed in TC compared to primary mouse keratinocytes (Fig.…”

“…All animal experimental protocols were approved by the IACUC and the Animal Experimental Ethics Committee of the Carlos III Health Institute (Madrid, Spain), in accordance with National and European regulations. The following commercially available mouse lined were used: CD68CreERT2 (Tg(Cd68-creERT2)31.11.ICS, Institut Clinique de la Souris), K15CrePR1 (Tg(Krt1-15-cre/PGR)22Cot/J, Jackson Labs #005249) 51 , LysMCre (B6.129P2-Lyz2tm1(cre)Ifo/J, Jackson Labs,#004781) 52 , Wls lox/flox (129S-Wlstm1.1Lan/J, Jackson Labs, #012888) 24 , TCF/Lef1-EGFP (Tg(TCF/Lef1-HIST1H2BB/EGFP)61Hadj/J, Jackson Labs, #013752) 53 and K15GFP (Krt1-15-EGFP2Cot, Jackson Labs, #005244) 51 . Mice were backcrossed to C57BL/6J mice.…”

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

“…Strong expression of CD99 has also been reported in immature basal keratinocytes [ 47 ], in osteoblasts [ 18 , 48 ], and, at variable levels, in mesenchymal stem cells [ 49 ]. For more details refer to Pasello [ 33 ].…”

“Neuroectodermal influence of CD 99 immunoexpression correlates with the clinical behavior of odontogenic cysts and tumors”

“…CD 99 is strongly expressed in immature basal keratinocytes and there is an evidence for strong positivity of CD 99 for populations of stem cells located at the basal layer of the epidermis and the hair follicle bulge. [ 6 ] It is involved in many essential cellular functions such as cell adhesion and migration, cell death and differentiation, intracellular protein trafficking, endocytosis and exocytosis, and metastasis of tumor cells through multiple and still controversial mechanisms of action, thereby emerging as a novel therapeutic target. [ 7 ]…”