Mucosal Immunity
Mucosal immunity refers to a defensive mechanism of the immune system located on the mucosal surfaces of the body, protecting against pathogenic invasion. The body is enveloped in a continuous structure composed of mucosa and skin, forming a sealed system that blocks external pathogens. While our skin, the body’s largest organ, weighing about one-fifth of an adult’s body weight, offers a multi-layered barrier against external harm, the mucosa, which is about 400 square meters in area—far exceeding the skin’s area of 2 square meters—includes delicate, folded tissues lining the mouth, respiratory tract, digestive tract, and urogenital tract. These features make the mucosa particularly effective yet often underestimated in its specialized immune defense mechanisms to protect against pathogens.
The health of the mucosa is a hot topic in integrative medicine. Diseases related to mucosal damage are widespread, indeed spanning various medical specialties such as dentistry, dermatology, otolaryngology, and internal medicine. However, the extensive mucosal surface, the largest bodily area, tends to be overlooked due to the over-specialization in medical practice. As early as 2010, the journal “Nature” suggested that mucosal immunity would be a focal point for the next generation of medical advancements.
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The mucosal immune system is the most primitive immune system in vertebrates and was the first to evolve. In humans, numerous internal and external pathways and chambers are covered with a protective barrier called “mucosa,” from the oral cavity to the anus in the digestive tract, from the nasal cavities to the lungs in the respiratory tract, and throughout the urogenital system. The mucosa comprises one or several layers of epithelial cells and an underlying connective tissue layer. Some mucosae secrete a viscous protective fluid containing antibacterial lysozymes and immunoglobulins, which provide lubrication and protection. The mucosa acts like body armor, effectively shielding against external microbial and viral threats, and also performs multiple functions such as secretion, absorption, and sensation, offering comprehensive protection to the body.
Mucosal immunity involves not just the mucosal tissues but the intricate interplay between “mucosa-immunity-microbiome.” Recent studies indicate that a symbiotic microbial flora on the mucosal surface is part of innate immunity. The balance and disruption of this interaction are crucial for maintaining health or triggering inflammation.
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Recent medical research indicates that when viruses or pathogens invade the human body, the first line of defense—mucosal tissues—are crucial in preventing infectious diseases. Given that mucosa is distributed across vital organs, its systemic protection and care are increasingly seen as pivotal in new medical paradigms.
When mucosal integrity is compromised, whether due to a weakened immune system or side effects of medications, pathogens can more easily infiltrate the body. This explains why cancer patients may develop oral mucositis and sepsis, why chronically bedridden patients must maintain oral hygiene to prevent aspiration pneumonia, and why leaky gut syndrome (LGS) is associated with systemic chronic inflammation.
The World Health Organization (WHO) has identified chronic inflammatory diseases as the greatest threat to human health. Two-thirds of deaths worldwide are due to diseases like stroke, chronic respiratory diseases, heart disease, cancer, autoimmune diseases, obesity, and diabetes—all linked to chronic inflammation. Chronic inflammation can impact daily life through pain, fatigue, restricted mobility, and sleep disorders, significantly affecting an individual’s quality of life.
Professor Kenneth K. Wu, a hematologist and academician at the Academia Sinica, has described chronic inflammation not as acutely painful but as insidious and silent. (慢性發炎不像急性發炎讓你日子難過，而是隱形的、靜默無聲的！)
Key to reducing the risk of chronic inflammation is a comprehensive understanding and protection of the mucosal immune system. Studies show that the mucosal immune system, as a whole organ, is crucial for maintaining microbial flora balance and regulating immune responses. Therefore, by promoting a healthy microbiome, maintaining the integrity of the mucosal barrier, and enhancing the function of immune cells, we can effectively lower the risk of chronic inflammation. This includes supporting mucosal immunity through a balanced diet, regular exercise, good personal hygiene, and the intake of probiotics.
