Vitalant Research Institute, San Francisco, California.
Department of Laboratory Medicine, University of California, San Francisco, California.
Transfusion. 2019 Nov;59(11):3501-3510. doi: 10.1111/trf.15516. Epub 2019 Oct 10.
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.
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.
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.
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.
富含血小板的血浆（PRP）输注的同种异体免疫会引起不良反应，如血小板反应性降低或移植排斥。用紫外线和核黄素（UV+R）对同种异体 PRP 进行病原体减少处理已被证明可降低同种异体抗体反应，并在小鼠中对随后的输注产生部分抗原特异性免疫耐受。研究表明，UV+R 既能迅速杀死供体白细胞（WBC），又能降低其在体外刺激同种异体反应的能力。然而，UV+R 诱导 WBC 死亡的方式及其在处理后的 PRP 免疫反应中的相关作用尚不清楚。
本研究通过流式细胞术检查质膜上的磷脂酰丝氨酸暴露、膜不对称性、半胱天冬酶活性和染色质浓缩，来评估 UV+R 是否通过 WBC 凋亡来诱导 WBC 死亡。还通过体内研究检查了用 UV+R 杀死的 WBC 的免疫原性与凋亡或坏死途径的关系。
UV+R 处理后的 WBC 表现出早期凋亡样特征，包括质膜外叶的磷脂酰丝氨酸暴露和膜不对称性丧失，但与经典的凋亡细胞不同，半胱天冬酶活性和染色质浓缩不明显。然而，体内研究表明，与未处理或坏死的 WBC 不同，凋亡的 WBC 和 UV+R 处理的 WBC 均不能引发随后未处理的输注的同种异体抗体反应。
总的来说，UV+R 处理后 WBC 死亡的机制与早期凋亡的一些膜特征相似，但与经典的凋亡不同。尽管存在这些差异，UV+R 处理的和凋亡的 WBC 都能提供一定的免疫保护作用，防止同种异体免疫。
