皮肤的表层即表皮，主要由角质细胞构成，占表皮层总细胞的90% [1], [2]。表皮在免疫反应中起重要作用，通过屏障作用阻止细菌、病毒、真菌及寄生虫的侵入 [1] 。表皮的防疫功能还包括保护水分丢失，对抗热和UV辐射等 [3]。

表皮分为基底层、棘层、颗粒层、透明层和角质层（图1）[4]。这些层含不同阶段的角质细胞 。角质形成过程包括一系列有丝分裂，这些分裂始于基底层，并导致细胞质被角质蛋白代替。角化过程结束时，角质细胞死亡；角质层中为扁平、无核、高度角化的鳞状细胞[4]。

板层小体和透明角质颗粒分析

不同于我们以前的NHEK拍摄的特征，在这个样本中，细胞核看起来是一个复杂的、高度分隔的细胞器（图3）。

这一现象可以解释为从基底层向颗粒层过渡过程中的多重分裂作用效果[7]，[8]，已知这些分裂主要包括在基底层水平上的一些不对称分裂，导致不同的细胞命运和大小 [9]，[10]。

事实上，与图左下角相邻的细胞相比，中间的细胞似乎尺寸明显增大。

[1]  J. A. McGrath, R. A. J. Eady, and F. M. Pope, “Anatomy and Organization of Human Skin,” in Rook’s Textbook of Dermatology, Malden, Massachusetts, USA: Blackwell Publishing, Inc., pp. 45–128.

[2] P. A. Kolarsick, M. Ann Kolarsick, and C. Goodwin, “Anatomy and Physiology of the Skin,” 2006.

[3]  Practical immunodermatology. Springer, 2017.

[4] H. Yousef, M. Alhajj, and S. Sharma, Anatomy, Skin (Integument), Epidermis. StatPearls Publishing, 2019.

[5] A. Gedeon Matoltsy and M. N. Matoltsy, “THE CHEMICAL NATURE OF KERATOHYALIN GRANULES OF THE EPIDERMIS.”

[6] R. Joshi, “Learning from eponyms: George F. Odland and Odland bodies,” Indian Dermatol. Online J., vol. 5, no. 3, p. 334, Jul. 2014.

[7] “Polyploid cells and nuclei in keratinocyte primary cultures. (a-c)… | Download Scientific Diagram.” [Online]. Available: https://www.researchgate.net/figure/Polyploid-cells-and-nuclei-in-keratinocyte-primary-cultures-a-c-photographs-of_fig4_12400529. [Accessed: 27-Aug-2019].

[8] M. R. Gdula et al., “Remodeling of Three-Dimensional Organization of the Nucleus during Terminal Keratinocyte Differentiation in the Epidermis,” J. Invest. Dermatol., vol. 133, no. 9, pp. 2191–2201, Sep. 2013.

[9] M. I. Koster and D. R. Roop, “Asymmetric Cell Division in Skin Development: A New Look at an Old Observation,” Dev. Cell, vol. 9, no. 4, pp. 444–446, Oct. 2005.

[10] H.-Y. JIA et al., “Asymmetric stem-cell division ensures sustained keratinocyte hyperproliferation in psoriatic skin lesions,” Int. J. Mol. Med., vol. 37, no. 2, pp. 359–368, Feb. 2016.