Changes of local microenvironment and systemic immunity after acupuncture stimulation during inflammation: A literature review of animal studies

Acupuncture is an ancient technique that consists of inserting fine needles into specific points on the body, called acupoints, to treat various health conditions. Although it has been practiced for thousands of years, only recently has modern science begun to unravel the biological mechanisms that explain how acupuncture produces its therapeutic effects. A particularly interesting aspect is the way acupuncture modulates the immune system — the set of cells and mechanisms that defend our body against infections and injuries. This study is especially relevant because many chronic diseases, such as rheumatoid arthritis, asthma, and inflammatory bowel diseases, involve immune system imbalances that acupuncture can help correct.

The objective of this study was to review and organize the current scientific knowledge about how acupuncture affects both local immune responses (at the site where the needle is inserted) and systemic responses (throughout the body). To this end, the researchers analyzed studies conducted in laboratory animals, focusing specifically on inflammatory processes. The methodology consisted of a narrative review of the scientific literature, in which the most relevant and recent studies on the subject were selected and analyzed. The authors organized their findings into two main categories: first, the changes that occur in the local environment where the needle is inserted, including the responses of different types of immune cells; second, how these local changes connect with alterations throughout the body via the nervous system.

The main findings of the study reveal a fascinating and complex mechanism. When an acupuncture needle is inserted into the skin, the body interprets this as a "sterile injury" — that is, an injury without the presence of microorganisms. This triggers a cascade of events involving different types of cells. Endothelial cells, which line blood vessels, release nitric oxide, a substance that dilates the vessels and improves local blood flow.

Neutrophils, defense cells that arrive first at the site, release anti-inflammatory substances such as TGF-β and IL-10, while reducing the production of pro-inflammatory molecules. Macrophages, cells specialized in "cleaning" damaged tissues, shift from an inflammatory profile (M1) to a reparative profile (M2). Mast cells, which are involved in allergic reactions, respond both to the chemical and mechanical stimuli of acupuncture, participating in the healing process. The rotational movement of the needle activates cells called fibroblasts, which are important for the formation of healthy scar tissue.

The study also found that these local changes communicate with the rest of the body through three main pathways of the nervous system. The first is the cholinergic anti-inflammatory pathway, which involves the vagus nerve and uses acetylcholine as a chemical messenger to reduce inflammation in organs such as the spleen. The second is the vagal-adrenal pathway, in which stimulation of the vagus nerve leads to the release of dopamine by the adrenal glands, producing systemic anti-inflammatory effects. The third is the splenic sympathetic pathway, which uses norepinephrine to modulate the immune response.

Interestingly, different intensities of electrical stimulation in acupuncture activate different pathways, explaining why specific techniques can have distinct effects.

For patients, these findings help explain why acupuncture can be effective in treating chronic inflammatory conditions. The technique not only treats symptoms but actually modulates the biological mechanisms underlying inflammation. This provides a solid scientific basis for the use of acupuncture as a complement to conventional treatments in diseases such as arthritis, asthma, inflammatory bowel diseases, and even in the recovery from strokes. For healthcare professionals, the study offers valuable insights into how to optimize treatments, suggesting that the choice of specific acupoints, intensity of stimulation, and technique used (manual versus electrical) can be adjusted based on the biological mechanisms one wishes to activate.

However, the study has important limitations that should be considered. First, all the research reviewed was conducted on laboratory animals, mainly mice and rats. Although these models are valuable for understanding basic mechanisms, we cannot automatically assume that the same processes occur identically in humans. Second, most studies focused on only a few specific acupoints, especially ST-36 (located on the leg), limiting our understanding of how other acupuncture points may function.

Third, many of the biological pathways described are extremely complex and may vary depending on the person's health status and the specific condition being treated.

This work represents a significant advance in the scientific understanding of acupuncture, providing a detailed map of how this ancient technique interacts with our immune and nervous systems. By connecting local responses with systemic effects, the study offers an integrated view that can guide future research and improve clinical practice. For patients considering acupuncture, these findings offer reassurance that there is a solid scientific basis behind the observed benefits. For the medical community, this knowledge opens doors to more personalized and effective treatments, potentially revolutionizing how we approach chronic inflammatory diseases.