弗氏海豚皮膚色素與傷口癒合之免疫調節研究

Abstract

皮膚傷口癒合的相關知識主要來自人類及實驗動物的研究，亦發現不同物種的皮膚組織學及免疫學有些相異之處，如：皮膚厚度、細胞類型、免疫反應等，而這些差異皆可能影響不同物種傷口癒合的過程。野外調查發現，鯨豚身上的深層皮膚傷口可以在未治療的狀況下自然痊癒。鯨豚傷口癒合的相關機制還未被了解，目前也尚無鯨豚深層皮膚傷口癒合的組織病理學研究。本研究以弗氏海豚的正常皮膚及達摩鯊咬傷之全厚度皮膚傷口為樣本，觀察不同傷口癒合階段之組織病理學變化，並進行多種化學染色及免疫組織化學染色，分析不同傷口癒合階段之抗原呈現細胞、T 細胞、角質素17 (keratin 17)、黑色素、黑色素細胞及膠原纖維的變化。本研究發現弗氏海豚的皮膚傷口癒合有以下幾個特色。一、在已癒合的深層皮膚傷口可觀察到皮釘與脂肪組織再生，而此現象未在人類身上觀察到。鯨豚深層皮膚傷口癒合過程中，只出現小範圍的炎症反應，可能與鯨豚皮膚良好的再生能力有關。二、在正常皮膚及傷口組織中有許多細胞同時表現第二類主要組織相容複合體 (major histocompatibility complex class II)和CD3，顯示γδ T 細胞 (γδ T cell) 可能是海豚皮膚組織中主要的免疫細胞，而典型的抗原呈現細胞及αβ T細胞 (αβ T cell)可能非常稀少。三、正在癒合中的表皮表現較多角質素17，顯示角質素17 可能有助於皮膚傷口再上皮化。四、傷口癒合的早期即可觀察到黑色素及黑色素細胞，此種獨特的現象可能有助於降低紫外線對新生表皮的傷害。另外亦發現黑色素細胞分布不均，即黑色皮膚有較多的黑色素細胞而白色皮膚的黑色素細胞較少。五、皮膚中的膠原纖維以第一型膠原纖維為主，第三型膠原纖維占的比例非常少，這類較硬的膠原纖維是鯨豚皮膚的主要纖維，可能有助於抵抗水壓及外界傷害。此為首篇鯨豚全厚度皮膚傷口癒合的研究，從組織學的角度展示了鯨豚強大的皮膚再生能力以及鯨豚皮膚傷口癒合與陸生動物的差異。本研究獲得的重要資訊將有助於人類再生醫學的發展。

Current knowledge of cutaneous wound healing is mostly based on the studies in laboratory animals and humans. The histological and immunological features of skin such as cutaneous thickness, cellular components and immune response are not identical among animal species, and these differences may lead to substantial effects in wound healing. In the field observation studies, it was noticed that deep cutaneous wounds in cetaceans could heal without any medical treatment. The underlying mechanisms which contribute to the incredible healing capacity in cetaceans are still unknown, and there is no published histological study on deep wound healing process in cetaceans. In the current study, the skin samples including normal skin and full-thickness wounds which caused by cookiecutter sharks (Isistius brasiliensis) bite were collected from stranded Fraser’s dolphins (Lagenodelphis hosei). Several histological staining techniques were performed to investigate the cellular and molecular changes during wound healing, including hematoxylin and eosin staining, Masson’s trichrome staining, Fontana-Masson staining, Herovici’s staining, and immunohistostaining for antigen-presenting cells, T cells, keratin 17, melanin, melanocytes, and collagens. It was noticed that several special characteristics in cutaneous wound healing in Fraser’s dolphins: (1) regeneration of rete ridges and adipose tissue were observed in completely healed deep wounds, which does not happen in human skin, and the remarkable regenerative capacity might be related to limited inflammatory response in dolphin cutaneous wounds; (2) numerous cells simultaneously expressed major histocompatibility complex class II and CD3 in the normal, healing and healed skin, indicating that γδ T cells might be the predominant immune cells and the typical antigen-presenting cells and αβ T cells might be rare in dolphin skin; (3) keratin 17 was highly expressed in the migrating epidermal tongue, suggesting that the expression of keratin 17 in cetacean skin might contribute to re-epithelialization during wound healing; (4) early appearance of melanin and melanocytes during wound healing might be the unique photoprotective strategy in cetaceans, and the distribution of melanocytes was uneven, which the number of melanocytes in dark skin was higher than that in white skin; (5) type I collagen was in the majority and type III collagen was rare in Fraser’s dolphin skin, indicating that dolphins could be able to endure water pressure due to the protection by stiff collagen fibers in skin. This is the first study on the histological features in full-thickness wound healing in cetaceans. The remarkable regenerative capacity of cetacean skin and the differences of wound healing between cetaceans and terrestrial mammals were shown from histological aspect in the current study. Understanding how cetaceans regenerate large full-thickness wounds in a harsh environment may contribute to the development of regenerative medicine in humans.