BIOCHEMICAL MODULATION OF IMMUNE RESPONSE IN VIVO AND IN VITRO

免疫细胞的正常发育和功能需要腺苷脱氨酶（ADA）活性。人体中ADA缺失或低水平可导致重度联合免疫缺陷（SCID），其特征为胸腺发育不全、T淋巴细胞耗竭和自身免疫。ADA SCID目前只能用积累的腺苷的细胞内光毒性来解释。我们最近提出细胞外腺苷（extAdo）在ADA-SCID发病机制中的信号传导作用，并且已经证明在ADA缺乏的条件下，extAdo拮抗TCR触发的信号传导并阻断胸腺细胞中活化标志物和早期活化事件的上调。我们发现在ADA缺乏的条件下，TCR触发的胸腺细胞在体外的长期（4天）存活是通过阻断腺苷转运蛋白介导的毒性细胞内腺苷的积累来实现的。存活的胸腺细胞具有非活化的表型，这是因为外消旋体介导的TCR拮抗信号传导。因此，实验数据与模型一致，其中腺苷的细胞内毒性主要负责淋巴细胞耗竭，而extAdo干扰在ADA缺乏条件下存活的20%至30%的T细胞的正常分化和功能。我们正在进行的ADA缺陷小鼠的研究被认为是人类ADA SCID疾病的模型，但由于其寿命短而变得复杂。由于小鼠在出生后约25天死亡，因此对其免疫系统功能的分析主要限于短期读数和离体淋巴细胞的分析。实验正在进行中，以测试ADA缺陷小鼠体内胸腺细胞和T细胞活化受到影响的预测。- 腺苷脱氨酶，免疫缺陷，T细胞，细胞外腺苷，嘌呤能受体

Normal development and functions of immune cells require adenosine deaminase (ADA) activity. Absence or low-level ADA in humans results in severe combined immunodeficiency (SCID), which is characterized by hypoplastic thymus, T lymphocyte depletion, and autoimmunity. ADA SCID is currently explained only by intracellular lymphotoxicity of accumulated adenosine. We recently proposed the signaling role of extracellular adenosine (extAdo) in pathogenesis of ADA-SCID and it has been demonstrated that under conditions of ADA deficiency, extAdo antagonizes TCR-triggered signaling and blocks the upregulation both of activation markers and of early activation events in thymocytes. We found that under conditions of ADA deficiency, long-term (4-day) survival of TCR-triggered thymocytes in vitro was accomplished by blocking the adenosine transporter-mediated accumulation of toxic intracellular adenosine. The surviving thymocytes had nonactivated phenotype because of extAdo-mediated, TCR-antagonizing signaling. Thus, the experimental data are consistent with the model where the intracellular toxicity of adenosine is mostly responsible for lymphocyte depletion, whereas extAdo interferes with normal differentiation and functioning of those 20% to 30% of T cells that do survive under conditions of ADA deficiency. Our ongoing studies of ADA- deficient mice considered to represent a model of the ADA SCID disease in humans are complicated by their short life span. Because mice die at about 25 days after birth, the analysis of their immune system functioning is limited to mostly short-term read-outs and analysis of ex vivo lymphocytes. Experiments are in progress to test the prediction that thymocyte and T cell activation in vivo are affected in ADA deficient mice. - Adenosine deaminase, immunodeficiency, T-cells, extracellular adenosine, purinergic receptors