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Updated: Jan 6, 2026
Inactivation of Pathogens via Visible-Light Photolysis of Riboflavin-5′-Phosphate
Published on: April 6, 2022
Pathogen reduction with riboflavin and ultraviolet light induces a quasi-apoptotic state in blood leukocytes
Johnson Q Tran1, Marcus O Muench1,2, John W Heitman1
1Vitalant Research Institute, San Francisco, California.
Background:
Alloimmunization to platelet-rich plasma (PRP) transfusions can cause adverse reactions such as platelet refractoriness or transplant rejection. Pathogen reduction treatment with ultraviolet light and riboflavin (UV + R) of allogeneic PRP was shown to reduce allogeneic antibody responses and confer partial antigen-specific immune tolerance to subsequent transfusions in mice. Studies have shown that UV + R was effective at both rapidly killing donor white blood cells (WBCs) and reducing their ability to stimulate an allogeneic response in vitro. However, the manner in which UV + R induces WBC death and its associated role in the immune response to treated PRP is unknown.
Methods And Materials:
This study evaluates whether UV + R causes WBC apoptosis by examining phosphatidylserine exposure on the plasma membrane, membrane asymmetry, caspase activity, and chromatin condensation by flow cytometry. The immunogenicity of WBCs killed with UV + R versus apoptotic or necrotic pathways was also examined in vivo.
Results:
WBCs after UV + R exhibited early apoptotic-like characteristics including phosphatidylserine exposure on the outer leaflet of the plasma membrane and loss of membrane asymmetry, but unlike canonical apoptotic cells, caspase activity and chromatin condensation were not apparent. However, in vivo studies demonstrated, unlike untreated or necrotic WBCs, both apoptotic WBCs and UV + R-treated WBCs failed to prime alloantibody responses to subsequent untreated transfusions.
Conclusion:
Overall, the mechanism of WBC death following UV + R treatment shares some membrane characteristics of early apoptosis but is distinct from classic apoptosis. Despite these differences, UV + R-treated and apoptotic WBCs both offer some protection from alloimmunization.
Insights
Pathogen reduction treatment (UV+R) of platelet-rich plasma (PRP) causes white blood cell (WBC) death with early apoptotic features. Both UV+R-treated and apoptotic WBCs reduce alloimmunization risk from subsequent transfusions.
Area of Science:
- Immunology
- Transfusion Medicine
- Cell Biology
Background:
- Alloimmunization to platelet-rich plasma (PRP) transfusions can lead to adverse reactions like platelet refractoriness and transplant rejection.
- Pathogen reduction treatment using ultraviolet light and riboflavin (UV+R) has shown potential in reducing antibody responses and inducing immune tolerance to allogeneic PRP in mice.
- UV+R treatment effectively kills donor white blood cells (WBCs) and diminishes their allogeneic stimulatory capacity in vitro, but the mechanism of WBC death and its immune role remain unclear.
Purpose of the Study:
- To investigate the mechanism of WBC death induced by UV+R treatment.
- To evaluate the role of UV+R-induced WBC death in the immune response to treated PRP.
- To compare the immunogenicity of UV+R-treated WBCs with those undergoing apoptosis or necrosis in vivo.
Main Methods:
- Flow cytometry was used to assess WBC apoptosis by examining phosphatidylserine exposure, membrane asymmetry, caspase activity, and chromatin condensation.
- In vivo studies were conducted to evaluate the immunogenicity of WBCs treated with UV+R versus those undergoing apoptosis or necrosis.
Main Results:
- WBCs treated with UV+R exhibited early apoptotic characteristics, including phosphatidylserine exposure and loss of membrane asymmetry.
- Unlike canonical apoptosis, UV+R-treated WBCs did not show significant caspase activity or chromatin condensation.
- In vivo, both apoptotic WBCs and UV+R-treated WBCs failed to prime alloantibody responses to subsequent untreated transfusions, unlike untreated or necrotic WBCs.
Conclusions:
- The mechanism of WBC death induced by UV+R shares some membrane features with early apoptosis but is distinct from classical apoptosis.
- Both UV+R-treated WBCs and apoptotic WBCs provide a degree of protection against alloimmunization.
- These findings suggest that UV+R treatment may offer a strategy to mitigate alloimmunization risks associated with PRP transfusions.
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