AS2O3对CD34+白血病细胞NKG2D配体表达及NK杀伤活性的影响

目的：观察AS2O3对CD34^＋早期急性髓系白血病细胞NKG2D配体表达及NK细胞杀伤活性的影响。方法：流式细胞仪检测KG1a细胞表面CD34抗原表达率,MTT法确定AS2O3的基本工作浓度,以不同浓度的AS2O3处理KG1a细胞,流式细胞仪测定处理前后KG1a细胞NKG2D配体的表达情况;MACS法分离5例健康个体的NK细胞,LDH释放法检测NK细胞对AS2O3处理前后KG1a细胞的杀伤活性。结果：10nmol/ml的AS2O3作用KG1a细胞后,能使KG1a细胞表面ULBP1的表达水平显著上调（P〈0.05）,同时也激发了NK细胞对KG1a细胞的杀伤活性（P〈0.05）。结论：AS2O3能上调CD34^＋白血病细胞表面NKG2D配体的表达水平,诱导NK细胞对其的杀伤活性,启示AS2O3可与NK细胞组成过继性免疫化疗方案,提高急性白血病的疗效。     

三氧化二砷提高多发性骨髓瘤ARH-77细胞对NK细胞杀伤敏感性的研究

目的 研究三氧化二砷(arsenic trioxide,ATO)前后人多发性骨髓瘤ARH-77对NK细胞杀伤细胞敏感性的变化,并初步探讨其机制.方法 分别应用CCK-8法和台盼蓝染色法测算ATO对ARH-77细胞株的50%抑制量(IC50)和细胞活性;乳酸脱氢酶释放法检测ATO作用前后ARH-77细胞对NK细胞的杀伤敏感性.流式细胞仪检测ARH-77细胞表面NKG2D配体(MICA/B、ULBP1、ULBP2、ULBP3)和HLA-Ⅰ类分子表达以及ATO作用前后的细胞周期变化.结果 ATO对ARH-77细胞的IG50为5.0μmol/L.NK 细胞杀伤ATO作用前后ARH-77细胞的活性有显著差异(P＜0.05).ATO作用后,ARH-77细胞发生G1/S期阻滞,同时其表面MICA/B、ULBP1、ULBP3表达显著升高,二者之间差异有统计学意义(P＜0.05).ULBP2和HLA-Ⅰ类分子无明显变化(P＞0.05).结论 ATO能提高ARH-77细胞NKG2D配体(MICA/B、ULBP1、ULIBP3)表达;从而使其对NK细胞的杀伤敏感性增强.     

沙利度胺对白血病细胞NKG2D配体表达及NK细胞杀伤敏感性的影响

目的:探究沙利度胺对白血病细胞自然杀伤细胞及活性受体D(natural killer cell group 2 member D,NKG2D)配体表达及自然杀伤细胞(natural killer,NK)杀伤敏感性的影响.方法:取对数生长期白血病细胞株HL-60、K562细胞,以不同浓度沙利度胺作用48 h,并设置未经沙...     

和厚朴酚增强NK-92细胞对KG-1a细胞的杀伤作用及机制研究

目的:观察和厚朴酚是否增强NK-92细胞对人急性髓细胞白血病KG-1a细胞的杀伤作用,并探讨其机制.方法:CCK8法检测和厚朴酚对KG-1a细胞的毒性作用,乳酸脱氢酶(lactate dehydrogenase,LDH)法检测NK-92细胞对KG-1a细胞的杀伤作用,流式细胞术检测和厚朴酚对KG-1a细胞凋亡的影响以及...     

NKG2D配体在NK细胞杀伤三氧化二砷诱导的KG1a细胞中的作用

目的:探讨低浓度的三氧化二砷(ATO)作用急性髓系白血病KG1a细胞株后,对KG1a细胞增殖的影响及与NK细胞联合杀伤肿瘤细胞可能的作用机制.方法:XTT法检测不同浓度ATO对KG1a细胞24 h、48 h的细胞生长抑制作用;LDH检测试剂盒检测定NK细胞对KG1a细胞的杀伤作用;甲基纤维素集落形成实验检测不同实验处理...     

白藜芦醇增强TRAIL对人髓系白血病KG-1a细胞的细胞毒作用

目的:观察白藜芦醇作用前后TRAIL对人髓系白血病KG-1a细胞的细胞毒作用的变化。方法:流式细胞仪检测KG-1a细胞表面CD34和CD38的表达,二甲氧唑黄(XTT)细胞增殖及细胞毒性检测试剂盒检测白藜芦醇作用前后TRAIL对KG-1a细胞增殖的影响,AnnexinV-FITC/PI染色流式细胞仪检测细胞凋亡变化。流式细胞仪检测白藜芦醇作用前后KG-1a细胞表面TRAIL死亡受体表达变化。结果:人髓系白血病KG-1a细胞CD34+CD38-占(58.67±2.87)%,10~1 000 ng/ml的TRAIL对KG-1a细胞增殖无明显影响,但对白藜芦醇作用后的KG-1a细胞的增殖有明显抑制作用,白藜芦醇能促进TRAIL诱导KG-1a细胞凋亡,并能上调KG-1a细胞表面TRAIL死亡受体DR5的表达。结论:白藜芦醇能增强TRAIL对人髓系白血病KG-1a细胞的细胞毒作用,其机制可能与白藜芦醇上调KG-1a细胞表面TRAIL死亡受体DR5的表达有关。     

白血病细胞系NK细胞配体表达及其对NK-92细胞杀伤敏感性的研究

目的:检测白血病细胞系NK配体表达情况以及对NK-92细胞的敏感性,探讨NK配体表达与NK杀伤敏感性的关系。方法:通过半定量RT-PCR的方法,以β-actin为内参基因,分别检测U937、CEM、KG-1a、HL-60、NB4、Reh和LCL等7种细胞表面MICA、MICB、ULBP1、PVR、Nectin-2、LFA-3、LLT-1、HLA-E、HLA-F和HLA-G等10种NK配体的表达情况。通过流式细胞术,用CFSE和PI双染法,检测NK-92细胞对以上7种白血病细胞系的杀伤效应。结果:根据NK-92细胞对靶细胞的杀伤效应强弱,将以上7种白血病细胞系分成NK敏感组(U937,CEM,KG-1a)、中度敏感组(HL-60、NB4)和不敏感组(Reh,LcL)三组。NK配体PVR和HLA-F在组间的差异具有统计学意义(P值分别为0.017和0.016),不敏感组的PVR转录水平最低而HLA-F水平最高,其他配体间则无显著性差别。结论:本研究初步表明PVR和HLA-F是人为干预肿瘤细胞耐受NK细胞的两个靶点分子。     

自然杀伤细胞对高与低表达ABCG2的人耐药鼻咽癌细胞杀伤作用

目的:探讨自然杀伤(NK)细胞对高与低表达三磷酸腺苷(ATP)结合转运蛋白G超家族成员2(ABCG2)人多药耐药鼻咽癌CNE2/DDP细胞(ABCG2High细胞、ABCG2Low细胞)的杀伤活性差异.方法:利用免疫磁珠技术分离ABCG2High及ABCG2LowCNE2/DDP细胞、NK细胞,LDH释放测定法检测NK细胞对K562细胞、ABCG2High<及ABCG2LowCNE2/DDP细胞的杀伤活性,流式细胞技术(FCM)检测两种靶细胞NKG2D配体表达率及杀伤后靶细胞凋亡率.结果:ABCG2High、AB-CG2Low CNE2/DDP细胞分离后ABCG2表达率分别为(91.40±2.32)%、(1.70 ±0.24)%,分选后NK细胞CD3-CD16+CD56+细胞的纯度达90%以上,LDH释放测定法检测结果显示,在效靶比为10 vs 1、20 vs 1时,NK细胞对ABCG2Low细胞、ABCG2High细胞及K562细胞的杀伤率以ABCG2High曲细胞最高,凋亡率检测结果显示ABCG2HighCNE2/DDP细胞的凋亡率为(12.90±1.51)%,ABCG2LowCNE2/DDP细胞的凋亡相率为(6.13±0.85)%,NKG2D配体表达率检测结果显示AB.CG2High CNE2/DDP细胞5种NKG2D配体(MICA、MICB、ULBP1、ULBP2、ULBP3)表达率高于ABCG2LowCNE2/DDP细胞.结论:ABCG2HighCNE2/DDP细胞比ABCG2LowCNE2/DDP细胞更容易被NK细胞杀伤,其初步的机制是ABCG2HighCNE2/DDP细胞NKG2D配体表达率高于ABCG2LowCNE2/DDP细胞,导致了ABCG2HighCNE2/DDP细胞对NK的杀伤敏感性增强.     

急性髓细胞性白血病患者外周血单个核细胞CD28 mRNA的表达

背景：大量研究显示,肿瘤患者外周血T细胞表面共刺激分子CD28蛋白表达存在差异,提示共刺激通路异常可能与恶性肿瘤的发生进展有关。 目的：观察急性髓细胞性白血病外周血单个核细胞共刺激信号分子CD28 mRNA在中的表达。 方法：急性髓细胞性白血病患者80例,其中M0型7例,M1型6例,M2型18例,M3型15例,M4型17例,M5型9例,M6型8例。并根据急性白血病疗效标准将80例患者分为完全治愈组、缓解组、未缓解组。采用Taqman探针实时荧光定量PCR检测80例患者及76名健康人群外周血单个核细胞CD28 mRNA的表达。 结果与结论：急性髓细胞性白血病外周血单个核细胞M1,M3和M4亚型中的CD28 mRNA表达量低于健康人群 (P< 0.05);急性髓细胞性白血病未缓解组中CD28 mRNA低于健康人群 (P < 0.05),完全治愈组和缓解组中CD28 mRNA表达与健康人群差异无显著性意义。说明急性髓细胞白血病患者外周血单个核细胞存在CD28 mRNA表达缺陷,并与临床分期、病情进展及预后有关。     

吉非替尼上调NKG2D配体表达增强A549细胞对NK细胞杀伤的敏感性北大核心CSCD

目的:研究表皮生长因子受体酪氨酸激酶抑制剂吉非替尼对人肺腺癌A549细胞NKG2D配体表达及NK细胞杀伤活性的影响及其分子机制。方法:MTT法测定吉非替尼对A549细胞增殖抑制率,流式细胞仪检测吉非替尼、EGFR下游分子LY294002(PI3-K抑制剂)、SB203580(MAPK抑制剂)、STAT21(STAT3抑制剂)、Rottlerin(PKC抑制剂)作用A549细胞24小时后A549细胞NKG2D配体的表达。乳酸脱氢酶释放法检测不同效靶比时,NK细胞对吉非替尼作用前、后A549细胞的杀伤活性。结果:吉非替尼上调A549细胞MICB、ULBP1表达,增强A549细胞对NK细胞杀伤的敏感性,EGFR下游分子MAPK、STAT3抑制剂不影响A549细胞NKG2D配体的表达,PI3-K抑制剂下调A549细胞MICA表达,PKC抑制剂上调ULBP1表达。结论:吉非替尼上调NKG2D配体表达增强A549细胞对NK细胞杀伤的敏感性。     

Certain anti-CD34 monoclonal antibodies induce homotypic adhesion of leukemic cell lines in a CD18-dependent and a CD18-independent way

CD34 is a highly glycosylated type I membrane protein expressed by early hematopoietic progenitor cells as well as by endothelial cells and a subset of bone marrow stromal cells. CD34 is thought to play an important role during early hematopoiesis, although its function is unknown. We demonstrate that triggering of CD34 results in a rapid and vigorous homotypic adhesion in CD34⁺ cell lines, thereby providing evidence for a cell-cell adhesion function of CD34. The cellular adhesion event, induced by only two anti-CD34 mAb, (Immu-133 and QBend-10) was dependent on metabolic energy, an intact cytoskeleton and the presence of divalent cations. Analysis of antibody inhibition experiments indicated that the aggregation process partially involved the CD18 molecule.     

Selective increase of activation antigens HLA-DR and CD38 on CD4+ CD45RO+ T lymphocytes during HIV-1 infection.

Infection with HIV results in a progressive depletion of CD4+ T cells and leads to significant in vivo lymphocyte phenotype changes. In this regard, the expression of HLA-DR and CD38 on CD8+ T cells has been shown to increase dramatically with disease progression. We investigated the expression of both activation markers on CD4+ T cells in HIV-1-infected subjects at different clinical stages of infection and compared the in vivo activation of CD4+ T cells with parameters of viral activity and CD8+ T cell activation. Fresh peripheral venous blood was obtained from 54 HIV-infected subjects and from 28 uninfected healthy controls. Three-colour immunophenotyping of the CD4+ T cell subset showed that the proportion of CD4+ T cells expressing HLA-DR (10% in HIV-negative controls) or CD38 (62% in HIV-negative controls) was higher in asymptomatic (P < 0.05 for CD38) and symptomatic (P < 0.001 for HLA-DR and CD38) HIV-infected subjects than in controls, whereas the proportion of CD4+ T cells expressing CD45RO (54% in controls) remained relatively unchanged. Simultaneous expression of HLA-DR and CD38 on CD4+ T cells increased from 2.3% in controls to 11% (P < 0.001) in asymptomatic and 22% (P < 0.001) in symptomatic HIV-infected subjects. This relative increase of CD38 and HLA-DR expression occurred mainly on CD4+ T cells co-expressing CD45RO. Changes in expression of HLA-DR and CD38 on CD4+ T cells correlated with similar changes on CD8+ T lymphocytes, with the presence of HIV antigen in the circulation, and with the disease stage of HIV infection.     

Prognostic Values of CD38+CD101+PD1+CD8+ T Cells in Pancreatic Cancer

Programmed death-1 (PD-1), a key immune checkpoint molecule, has been developed as an oncotherapy target for various carcinomas. However, treatment with anti-PD-1 elicited only a minimal effect in pancreatic ductal adenocarcinoma (PDAC). Subsequent studies revealed the existence of a subset of PD-1⁺ T cells coexpressing CD38 and CD101, representing a fixed dysfunctional subpopulation that are not able to be rescued by anti-PD-1 immunotherapy. However, whether this subpopulation of PD-1 expressing CD8⁺ T cells could be useful in predicting PDAC stage or prognosing survival is unknown. In this study, we used flow cytometry and immunofluorescence assay to analyze the expression of CD38 and CD101 in 183 clinical PDAC samples, including 84 of peripheral blood and 99 of surgical tissues. High coexpression of CD38/CD101 on peripheral PD-1⁺CD8⁺ T cells or tumor-infiltrating lymphocytes (TILs) was found to be most significantly correlated with Tumor/Node/Metastasis (T/N/M) classification and clinical stage, in contrast PD-1⁺CD8⁺ T cells could not correlate with T classification. CD38/CD101 co-repression on TILs also correlated with the poor survival in these PDAC patient samples. Our data suggest that CD38/CD101 might represent a more helpful biomarker than PD-1 alone for diagnosis and prognosis of PDAC.     

CD34~+细胞免疫亲合柱的研制

本文建立了利用免疫亲合柱纯化CD34+细胞的方法。将亲合素交联于聚丙烯酰胺凝胶Bio Gel上 ,装于塑料柱制成免疫亲合柱 ;将脐血单个核细胞与生物素化抗CD34单克隆抗体作用后 ,加到该免疫亲合柱上进行纯化 ,得到纯化的CD34+细胞。纯化后CD34+细胞纯度达 48 8%± 18 2 % ,细胞回收率为 5 5 6 %± 14 5 % ,台盼蓝染色法显示活细胞达 98%。利用该方法纯化CD34+细胞具有纯度高、回收率高、细胞活性好等优点 ,是一种方便有效的细胞纯化方法。     

抗CD40抗体联合诱导人脐血CD34+造血干细胞向DC2分化的作用

目的 探讨从脐血CD34^＋造血细胞诱导DC2的方法及CD40分子在DC2分化诱导中的作用。方法 运用磁珠从脐血中分离出CD34^＋造血干细胞,以rhIL-3（10ng／mL）、rhFlt-3L（100ng／mL）和rhGM-CSF（100ng／mL）诱导其向DC2分化,采用流式细胞仪分析DC2表型,并观察抗人CD40单克隆抗体诱导DC2分化成熟的作用。结果 人脐血CD34^＋造血细胞在rhIL-3、rhFlt-3L和rhGM-CSF联合诱导培养12d,获得具有DC2样（淋巴样DC）形态的细胞,然后分别加入rhIL-3＋抗人CD40 mAb（Ⅰ组）或rhIL-3＋TNF-α（Ⅱ组）诱导DC2的分化成熟,流式细胞仪分析细胞表型,发现Ⅰ组和Ⅱ组Lineage^-（CD3、CD14、CD16、CD19、CD56）CD123^＋细胞的HLA-DR、CD83、CD86、CD80表达率分别为88．78％、37．38％、32．83％和99．08％;78．87％、32．29％、29．57％和98．86％。结论 体外联合多种细胞因子从CD34^＋造血细胞成功地诱导出富集DC2表型的细胞,抗人CD40 mAb可以促进DC2的分化成熟。     

重组人IL-12和SCF促进新生儿脐带血中CD34~+细胞的分裂增殖

目的分析IL-12及SCF对CD34+细胞分裂增殖及IL-12Rβ的表达。方法分离正常足月产新生儿脐带血与健康成年人外周血中的单个核细胞,采用流式细胞术(FACS)比较2组中CD34+细胞的频率,分析IL-12及SCF对CD34+细胞的作用。结果健康成年人外周血中CD34+细胞平均频率为0.13%,显著低于新生儿脐带血中CD34+细胞的平均频率1.53%(P<0.001)。进一步研究表明,SCF可以促进CD34+细胞表达CD25;IL-12及SCF可以显著促进CD34+细胞的分裂增殖以及IL-12Rβ1的表达。结论新生儿脐带血中CD34+细胞的频率明显高于成年人外周血中CD34+细胞的频率。IL-12及SCF可以促进CD34+细胞的分裂增殖以及IL-12Rβ1的表达。     

两步法从慢性髓系白血病患者骨髓CD34+细胞体外扩增诱导树突状细胞

目的探讨从慢性髓系白血病(CML)患者骨髓CD34~ 细胞体外扩增诱导树突状细胞(DC)的可行性,并比较CML-DC和正常DC的生物学特性。方法免疫磁珠法从CML患者和正常供者骨髓纯化CD34~ 细胞,在有血清条件下应用两步法:干细胞生长因子(SCF) FLT3配体(FL) 促血小板生成素(TPO) 白细胞介素-3(IL-3)扩增2周,然后以粒细胞巨噬细胞集落刺激因子(GM-CSF) 白细胞介素-4(IL-4) 肿瘤坏死因子-α(TNF-α)(GI方案)诱导DC。通过相差显微镜、电子显微镜、流式细胞仪分析DC的生物学特性,荧光原位杂交(FISH)检测培养前后CML细胞的bcr/abl融合基因表达。结果诱导后细胞较0d或诱导前细胞高表达DC相关抗原(CD1a,CD80,CD86,CD40,CD54,HLA-DR)。CML患者和正常供者CD34 细胞经GI方案诱导10d,CD1a阳性率分别为36.90%±26.94%和54.35%±16.34%,CD1a~ DC数是0d接种细胞的(54±54)倍和(122±129)倍。两组相比,总细胞扩增倍数、DC扩增倍数、细胞表型均无明显差异,诱导后的DC具有相似的超微结构。CML患者CD34~ 细胞诱导10d后bcr/abl融合基因阳性率为43.67%±21.55%,具有典型DC形态的细胞bcr/abl融合基因阳性率为53.2%。结论两步法GI方案能诱导CMLCD34~ 细胞产生大量DC,诱导生成的DC不但具有正常DC的典型形态、表型,而且起源于CML细胞。     

骨髓间充质干细胞对骨髓CD34~+细胞增殖影响的体外研究

研究骨髓间充质干细胞(bone marrow mesenchymal stem cell,BMMSC)对骨髓CD34+细胞增殖的影响,为骨髓CD34+细胞体外扩增的深入研究提供依据。用MACS进行骨髓CD34+细胞的分选;用流式细胞术进行CD34+细胞纯度鉴定;用密度梯度离心法分离引产胎儿骨髓单个核细胞,结合贴壁法进行BMMSC的体外扩增培养;用流式细胞术进行BMMSC表面标志鉴定;用Transwell培养板培养CD34+细胞与BMMSC;用自动细胞计数仪计数有活性的CD34+细胞数量;用MTT比色法检测骨髓CD34+细胞增殖活性。流式细胞术检测结果显示分选所得的CD34+细胞纯度达到90%以上;流式细胞术检测显示传至第3代继续培养72h后的BMMSC高表达CD44、CD29,而HLA-DR、CD45、CD34表达阴性,说明所培养的BMMSC纯度很高;Transwell培养板培养CD34+细胞与BMMSC,在倒置显微镜下观察以及自动细胞计数仪计数发现,实验组有活性的CD34+细胞数量高于对照组(P<0.05);采用MTT比色法检测骨髓CD34+细胞的增殖活性,实验组高于对照组(P<0.05)。以上结果说明BMMSC有促进骨髓CD34+细胞增殖的作用,这种作用可能与其分泌的细胞因子有关。     

Effects of intravenous human umbilical cord blood CD34+ stem cell therapy versus levodopa in experimentally induced Parkinsonism in mice

Introduction

Parkinsonism is a neurodegenerative disease with impaired motor function. The current research was directed to investigate the effect of CD34+ stem cells versus levodopa in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonism.

Material and methods

Mice were divided into 4 groups; saline-injected, MPTP: received four MPTP injections (20 mg/kg, i.p.) at 2 h intervals, MPTP groups treated with levodopa/carbidopa (100/10 mg/kg/twice/day for 28 days) or single intravenous injection of 10⁶ CD34+ stem cells/mouse at day 7 and allowed to survive until the end of week 5.

Results

Levodopa and stem cells improved MPTP-induced motor deficits; they abolished the difference in stride length, decreased percentage of foot slip errors and increased ambulation, activity factor and mobility duration in parkinsonian mice (p < 0.05). Further, they significantly (p < 0.05) increased striatal dopamine (85.3 ±4.3 and 110.6 ±5.3) and ATP levels (10.6 ±1.1 and 15.5 ±1.14) compared to MPTP (60.1 ±3.9 pmol/g and 3.6 ±0.09 mmol/g, respectively) (p < 0.05). Moreover, mitochondrial DNA from mice treated with levodopa or stem cells was in intact form; average concentration was (52.8 ±3.01 and 107.8 ±8.6) and no appreciable fragmentation of nuclear DNA was found compared to MPTP group. Regarding tyrosine hydroxylase (TH) immunostaining, stem cell group showed a marked increase of percentage of TH-immunopositive neurons (63.55 ±5.2) compared to both MPTP (37.6 ±3.1) and levodopa groups (41.6 ±3.5).

Conclusions

CD34+ cells ameliorated motor, biochemical and histological deficits in MPTP-parkinsonian mice, these effects were superior to those produced by levodopa that would be promising for the treatment of PD.     

Expression of human NKRP1A by CD34+ immature thymocytes: NKRP1A-mediated regulation of proliferation and cytolytic activity

In this study, we show that NKRP1A is expressed and functions on a subset of immature human thymocytes. We took advantage of the monoclonal antibody (mAb) 191B8 that was obtained by immunizing mice with cultured human thymocytes characterized by an immature surface phenotype [CD2^? CD3^? CD4^? CD8^? stem cell factor receptor (SCFR)⁺] and expressing cytoplasmic CD3? chain. The 191B8 antibody homogeneously reacted with the immunizing population but not with most unfractionated thymocytes. It stained a minor population of resting immature thymocytes co-expressing CD34, SCFR, or both. Following culture of the CD34⁺ or CD34^? fractions of CD2^? CD3^? CD4^? CD8^? purified immature thymocytes with recombinant interleukin-2 (rIL-2), the 191B8-defined antigen was expressed on virtually all cells even when 191B8⁺ cells were removed from the starting population. On the other hand, no 191B8⁺ cells were detected in fresh or cultured thymocytes expressing a more mature phenotype. Biochemical analysis of 191B8 mAb-reactive molecules revealed, under non-reducing conditions, two bands displaying apparent molecular masses of 80 and 44 kDa and a single band of 44 kDa under reducing conditions. Digestion with proteases indicated that the 80-kDa form represented a homodimeric form of two 44-kDa molecules, while deglycosylation with N-glycanase suggested the existence of four N-glycosylation sites. Transfection of COS7 or NIH3T3 cells with hNKRP1A cDNA showed that the 191B8 mAb recognized NKRP1A as shown by both immunofluorescence analysis and immu-noprecipitation experiments. Functional studies showed that the 191B8/NKRP1A molecule mediated strong inhibition of the cytolytic activity of culturd CD2^? CD3^? immature thymocytes against a panel of tumor target cells. More importantly, 191B8 mAb induced proliferation of CD2^? CD3^? fresh thymocytes which was not increased by rIL-2. Thus, we propose that NKRP1A molecules, which are expressed in highly immature thymocytes, may play a regulatory role in their growth and function.