The Natural Defenses of the Respiratory Tract

The Natural Defenses of the Respiratory Tract

The primary gas exchange function of the respiratory system makes it vulnerable to pathogens circulating in the air. However, the respiratory tract has physical and cellular apparatus that form the natural defenses against microbial entry and disease. Different types of cells make up and line the respiratory airways. They include goblet cells, epithelial cells, neuroendocrine cells, and secretory cells, which prevent harmful particles such as dust or microbes from depositing on the lower airway and alveolar surfaces. Ciliated epithelial cells propel the secretory barrier consisting of mucus, antibodies, and antimicrobial proteins upwards, trapping microbes and other particles and preventing them from reaching the lung (LeMessurier et al., 2020). In case of a breach of the secretory barrier, particles and microbes communicate with immune cells such as leukocytes, which elicit an innate immunity-mediated inflammatory response and repair mechanisms (Iwasaki, Foxman & Molony, 2017). The alveolar is not protected by cilia or mucus. Particles reaching the alveolar are neutralized by cells drawn from innate immunity (macrophages and dendritic cells) and adaptive immunity (B and T cells).

These natural defense mechanisms are adequate to protect the airway. While the mechanism appears rather basic, the interconnection between these mechanisms is rather complicated and surprisingly efficient. This is evident by the many upper respiratory tract infections that clear spontaneously. Common interventions that most people use to manage these infections aim at improving the symptoms and include rehydration, rest and alleviating nose blockage in case of common colds. Further, many pathological microbial populations have been fought and eliminated without the development of disease. These mechanisms are therefore sufficient to protect the airway. Nevertheless, the respiratory pathways’ natural defenses need support. These interventions include smoking cessation, exercising and healthy diets.

References

Iwasaki, A., Foxman, E. F., & Molony, R. D. (2017). Early local immune defenses in the respiratory tract. Nature Reviews Immunology, 17(1), 7-20.

LeMessurier, K. S., Tiwary, M., Morin, N. P., & Samarasinghe, A. E. (2020). Respiratory barrier as a safeguard and regulator of defense against influenza A virus and Streptococcus pneumoniae. Frontiers in immunology, 3.