HOW DOES PDT ACTIVATE the Innate Immune System TO FIGHT INFECTION:

  1. Direct Killing of Pathogens: ROS produced by PDT can directly kill pathogens by damaging their cell membranes, proteins, and DNA. This rapid destruction of microbial cells reduces the pathogen load and assists the immune system in clearing the infection.

  2. Release of Damage-Associated Molecular Patterns (DAMPs): The destruction of infected cells (host cells) and pathogens by PDT leads to the release of DAMPs. These molecules are recognized by pattern recognition receptors (PRRs) on innate immune cells like macrophages, neutrophils, and dendritic cells. The recognition of DAMPs activates these immune cells.

  3. Recruitment and Activation of Immune Cells: PDT can lead to the production of cytokines and chemokines that attract innate immune cells (such as neutrophils, macrophages, and natural killer cells) to the site of infection. This recruitment enhances the body’s ability to clear both the killed pathogens and any infected cells. Macrophages and neutrophils can also become more active and effective at phagocytosing (engulfing and digesting) pathogens after PDT.

  4. Enhanced Antigen Presentation: PDT can activate antigen-presenting cells (APCs) like dendritic cells, which take up pathogen-derived antigens from the site of infection and present them to T cells. This process is crucial for initiating and shaping an adaptive immune response, which can provide a more sustained defense against infection.

  5. Induction of Immunogenic Cell Death: PDT can cause immunogenic cell death, a form of cell death that stimulates the immune system. When PDT destroys infected cells, it exposes antigens from the pathogens to the immune system in an immunogenic context, thereby enhancing the body's ability to recognize and respond to infections.

Supporting references

  • Alves, E., Faustino, M. A., Neves, M. G., Cunha, Â., Nadais, H., Almeida, A. (2014). "Potential applications of porphyrins in photodynamic inactivation beyond the medical arena." An International Journal of Synthetic and Natural Product Chemistry, 76(12), 1509-1527.

   - This study discusses the antimicrobial effects of PDT and its ability to kill bacteria and other pathogens, thereby aiding the innate immune response.

  • Maisch, T. (2007). "Anti-microbial photodynamic therapy: Useful in the future?" Lasers in Medical Science, 22(2), 83-91.

   - This article explores the application of PDT in fighting infections and its role in enhancing the innate immune response, including the release of DAMPs and activation of immune cells.

  • Cieplik, F., Späth, A., Regensburger, J., et al. (2018). "Photodynamic biofilm inactivation by SAPYR—An exclusive singlet oxygen photosensitizer." Free Radical Biology and Medicine, 129, 8-16.

   - This study focuses on PDT's ability to eliminate biofilms, which are complex communities of bacteria that are highly resistant to conventional treatments, thereby highlighting PDT's role in activating innate immune mechanisms.

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