Phospholipase a2 contribution to thymocyte maturation and apoptotic thymocyte cell clearence

胸腺是T细胞成熟的器官。尽管已经描述了未成熟T淋巴细胞成熟的不同阶段，但所涉及的机制仍然不清楚，并在基础免疫学领域引起了人们的兴趣。据估计，每天在胸腺中产生5000万个未成熟的T细胞，并且只有200万个最终离开胸腺并到达血液循环。 有趣的是，虽然大多数未成熟的T细胞经历细胞死亡，但只有1-2%可以被检测为处于稳定状态的垂死细胞，这表明存在由垂死的T细胞递送的可溶性信号，以促进清道夫细胞（吞噬细胞）的迅速清除。有趣的是，脂质介质的产生被揭示为淋巴细胞成熟的机制，尽管脂质释放酶磷脂酶A2（PLA 2）在这一过程中的作用仍然不确定。我们发现分泌型PLA 2 X组-主要在胸腺中表达的分泌型PLA 2-参与凋亡胸腺细胞的清除。为了进一步了解PLA 2在T淋巴细胞成熟和凋亡中的作用机制，我们将追求以下目标： 目的1：明确胸腺淋巴细胞和非淋巴细胞中sPLA 2亚型的来源（细胞类型）。 目的2：探讨sPLA 2 X组表达对胸腺细胞成熟和凋亡的影响。 目的3：确定sPLA 2 X组在胸腺中的最终结果（下游生物合成产物） 使用药理学和遗传学的方法，我们将研究磷脂酶A2胸腺细胞成熟和凋亡胸腺细胞清除的贡献。虽然使用胸腺器官培养物和重组磷脂酶A2酶将允许描绘磷脂酶A2的体外机制，但缺乏磷脂酶A2表达的小鼠将提供磷脂酶A2体内作用的解剖方法。

The thymus is the organ where the maturation of T-cells occurs. Although the different stages of immature T-lymphocyte maturation have been described, the mechanisms implicated remain obscure and create fascination in the field of basic immunology. It is estimated that 50 million immature T-cells are generated each day in the thymus and that only 2 million ultimately leave the thymus and reach the blood circulation. Intriguingly, while most immature T-cells undergo cell death, only 1-2% can be detected as dying cells in the steady state, suggesting the existence of soluble signals delivered by the dying T-cells to promote prompt clearance by scavenger cells (phagocytes). Interestingly, the generation of lipid mediators was revealed to be a mechanism for lymphocyte maturation, though the role of lipid releasing enzymes phospholipase A2 (PLA2) in this process remained undefined. We found that secreted PLA2 group X - a secreted PLA2 mainly expressed in the thymus - participates to apoptotic thymocyte clearance. To gain further insight into PLA2 mechanism of action in T-lymphocyte maturation and apoptosis we will pursue the following Aims: Aim 1: Define the origin (cell type) of each sPLA2 isoforms expressed in thymic lymphoid and nonlymphoid thymic cells. Aim 2: Investigate the impact of sPLA2 group X expression on thymocyte maturation and apoptosis. Aim 3: Determine the final outcome (downstream biosynthetic products) of sPLA2 group X in the thymus Using both pharmacological and genetic approaches, we will study the contribution of phospholipase A2 to thymocyte maturation and apoptotic thymocyte clearance. While usage of thymic organ cultures and recombinant phospholipase A2 enzymes will permit delineation of phospholipase A2 mechanism in vitro, mouse lacking expression of phospholipase A2 will provide methods of dissection of phospholipase A2 action in vivo.