Clarification of acupoint essence is a core prerequisite for elucidating the mechanisms of acupuncture, yet the structural form of acupoints has not been fully clarified over the long term. Current research suggests that acupoint essence is related to specific structural systems, such as nerves, circulation, immunity, or fascia; however, these perspectives are not easily integrated. According to traditional Chinese medicine (TCM), acupoints along meridians are special locations of the human body where “qi” and “xue” flow in and out. Based on the novel concept that “Telocyte (TC) is a potential meridian parenchymal cell”, this study further investigated the role of TCs and their associated structures within acupoint regions, so as to provide new experimental evidence for elucidating the material basis of acupoints and revealing the principles underlying acupuncture effects.

The aim of this study was to clarify, using electron microscopy, the interactions between TCs and their elongated protrusion (telopode, Tp) within acupoint regions and various surrounding structural components, and to investigate whether specialized ultrastructural units related to acupoint functions exist, thereby providing a morphological foundation for elucidating the initial cellular responses to acupuncture.

The study subjects included commonly used acupoints in rats, mice, rabbits, and sheep. Focusing on the ultrastructure of acupoint regions, this study primarily employed electron microscopy techniques. It examined the spatial relationships and interactions between TCs and their Tp in acupoint regions and various components, including nerves, blood vessels, lymphatic vessels, immune cells, mast cells, extracellular vesicles (including exosomes), skin derivatives, acupoint matrix, and its fibers.

TEM revealed that TC and its Tp in the acupoint frequently entangled with or accompany various components, such as nerves, blood vessels, lymphatic vessels, immune cells, mast cells, extracellular vesicles (including exosomes), skin derivatives, acupoint matrix, and fibers. Some Tp even extended into the interior of structures, directly contacting or connecting with target components to form new structural units-“Telocyte-entanglement complexes” (TCEC). Notably, TC and its Tps could simultaneously entangle with one or multiple special components, thereby forming distinct morphological units among the TCECs. The extensive connectivity characteristic of TC indicated the ultrafine evidence of the "holistic view" concept in TCM. Furthermore, TC wrapped around fibers and forms developed adhesive spots, anchoring tightly to the matrix within acupoints, which might be conducive to explaining that TC was the initial cell of acupuncture effects. This observation provided the morphological evidence for the connective and integrative functions of TC within acupoint tissues and has been preliminarily validated by acupuncture.

The study systematically revealed the complex spatial relationships between TC and Tp within acupoint regions and various structural components, identifying a neglected ultrastructural unit - TCEC at acupoints. This structure reflected both the integration of local cells and tissues and provided a morphological foundation for understanding the initial cellular-mechanical responses to acupuncture. The findings not only clarified the biological basis of acupoints but also provided a new research perspective at the ultrastructural level for elucidating the mechanisms underlying acupuncture effects.

Meridian theory is the cornerstone of Traditional Chinese Medicine (TCM), and acupoints are the key sites on the meridian, which are the implementation location of the acupuncture. However, there are different opinions on the structural basis and morphological composition of acupoints, which cannot be scientifically clarified. As a newly found type of interstitial cells, Telocytes (TCs) were suggested to be the potential essence cells of the meridian by morphological study recently, but the characteristics and distribution of TCs at acupoints need to be further elucidated.

This study aimed to analyze the structural differences between acupoints and non-acupoints, and to explore the morphological characteristics of TCs at acupoints. The structural relations between TCs and its surrounding components were also analyzed, so as to provide theoretical support for the study of the cellular mechanism of TCM acupuncture treatment.

The skin tissues of Baihui (Du₂₀), Quchi (LI₁₁), Sanyinjiao (Sp₆), Danzhong (Ren₁₇), Chengjiang (Ren₂₄), Erjian (EP₄) and non-acupoints on the back and abdomen were collected from five adult healthy Hu sheep. TCs and Tps (telopodes) were stained by specific markers CD34 and Vimentin, the mast cells were labeled by TPS, and nerves were identified by PGP9.5. Extracellular vesicles were marked by TSG101. The structure and fine composition of skin acupoints and non-acupoints were analyzed by H.E and immunohistochemical techniques (IHC), and the morphological quantitative analysis of the data was carried out by using ImageJ and Image-Pro Plus statistical software. The distribution differences of TCs and its related structures at acupoints and non-acupoints were analyzed. On this basis, the morphological characteristics and stereoscopic structure of TCs were observed by transmission electron microscope (TEM), scanning electron microscope (SEM) and immunofluorescence (IF) double labeling technique, and the morphological relationship between TCs and these structures was further analyzed, thus determining the ultramorphology and material basis of acupoints.

There were such structures as hair follicles, sebaceous glands, sweat glands and arrector pili muscle, as well as nerves, blood vessels, mast cells, collagen fiber bundles at the acupoints and non-acupoints. However, the number of nerves, blood vessels and mast cells distribution at acupoints was significantly more than that at non-acupoints (P<0.05). More importantly, TCs with slender tubular processes (telopodes, Tps) were distributed in the skins, and the distribution of TCs at the acupoints was significantly different from that of non-acupoints (P<0.05). TCs could be used as the integrator of acupoints stroma. There were extensive relationships between TCs themselves or TCs and surrounding morphological structures (including gap junctions and extracellular vesicles, etc.), which could develop a structural network system. At the ultramicro level, it was observed that the Tps was a typical beaded appearance, which was composed of alternating arrangement of the inflated part (podom, Pd) and the slender stenotic part (podomer, P). The well-developed mitochondria in the cytoplasm of podom, the cellular connection between Tps and Tps, and a large number of extracellular vesicles on or around TCs (significantly more than non-acupoints (P<0.05)) ensured the core role of TCs in the structure of acupoints. Moreover, the structural connection between TCs and epidermal derivatives also verified the relationship between acupoints and epidermal derivatives in the classic book Huangdi Neijing (The Yellow Emperor’s Canon of Internal Medicine) at the cellular level.

Structural compositions at the acupoints and non-acupoints were basically the same, while the number of TCs and Tps, nerves, blood vessels, mast cells, extracellular vesicles at acupoints was significantly more than that at non-acupoints; TCs and Tps had the functional structures of connecting and integrating various morphological components, which might be mediators or integrators of different systems at the acupoints. The cell connections among TCs, developed mitochondria and extracellular vesicles had the structural basis for cell communication and energy generation, which corresponds to the “Qi-Xue” in TCM.