SPME-GC-MS结合ROAV分析单菌及复配发酵牛乳中关键性风味物质

采用固相微萃取-气相色谱-质谱联用技术检测分析Streptococcus thermophilus与Lactobacillus delbrueckii subsp.bulgaricus单菌及复配发酵牛乳中的挥发性风味物质,结合相对气味活度值(relative odor activity value,ROAV)探讨发酵牛乳中关键性风味物质。结果表明:本实验共鉴定出100种挥发性风味物质,包括酸类、酮类、醛类、醇类、酯类、烷烃类和芳香族类化合物等。主成分分析表明,表征S.thermophilus单菌发酵乳的关键性风味物质是双乙酰、正壬醛和甲苯;表征L.bulgaricus单菌发酵乳的关键性风味物质是正庚醛、丁酸-2-甲基丙酯和1-庚醇;表征S.thermophilus与L.bulgaricus复配发酵乳的关键性风味物质是乙醛、3-甲基正丁醛、乙偶姻、2-壬酮、2-庚酮、醋酸乙烯酯、碳酸庚基苯基酯、甲酸乙烯酯和2-壬醇。相较于单菌发酵,复配发酵的风味物质组成、各组分相对含量及关键性风味物质均发生改变。

保加利亚乳杆菌的筛选及其发酵乳中的风味物质

以分离自传统发酵乳中的7株保加利亚乳杆菌为试验菌株,测定发酵乳制作和贮藏(12 h)期间pH值、滴定酸度、活菌数、黏度的变化,并结合固相微萃取与气相色谱-质谱联用技术(SPME-GC-MS)检测贮藏12 h时发酵乳中的挥发性风味物质。结果表明,7株保加利亚乳杆菌中,IMAU62115在牛乳中的发酵时间最短(7 h),活菌数最高为4.95×108 CFU/mL,滴定酸度为95°T,黏度为820 mPa·s。贮藏12 h时,7株保加利亚乳杆菌发酵乳的风味成分差异显著,从IMAU20403、IMAU20396、IMAU62121、IMAU62115、IMAU20220、IMAU20227、IMAU20234中分别检出29,28,26,26,32,31种和26种风味物质,主要有酸类、醛类、酮类、醇类及酯类化合物等。其中,IMAU62115发酵乳中的主要特征性风味物质有双乙酰、乙偶姻、3-甲基丁醛、2-壬酮等,这些风味化合物在IMAU62115发酵乳中的浓度较高,OAV值大于1,对发酵乳的风味贡献较大。本研究筛选的保加利亚乳杆菌IMAU62115菌株是一株具有优良发酵特性的菌株。

Design of Car Based on 5G Network Control

The role of smart cars is pivotal,and this project designs and implements a four-wheel vehicle control system leveraging 5G communication technology.The system aims to enhance the portability of smart cars,reduce their costs,enable remote control functionality,and improve mobility to meet the needs of modern Internet of Things(IoT)applications.The system integrates an ESP8266 Wi-Fi module with the Blinker IoT platform to enable remote,real-time control of car movement via a smartphone app.Using Access Point(AP)mode for fast network configuration,users can input Wi-Fi credentials and a Blinker key through a web interface for easy setup.Through the custom app interface,users can send commands to control the car’s forward,backward,turning,and stopping actions,as well as adjust speed and operation delay.Additionally,the system includes Electrically Erasable Programmable Read-Only Memory(EEPROM)data storage to ensure the persistent saving of configuration information,and it features a remote wireless camera for external monitoring of the car’s surroundings.The Android-based remote control design allows users to monitor and control the car’s movement anytime and anywhere.Experimental results show that the system is stable,provides smooth control,operates at low cost and low power consumption,and offers good portability.Therefore,this intelligent car control system offers valuable insights for smart car development and application.It can also be integrated with popular smart homes,IoT,and other emerging technologies,offering broad application potential and promising development prospects.

氮源对嗜热链球菌胞外多糖表型特征的影响

乳酸菌胞外多糖(EPS)具有增加发酵乳黏度,防止乳清析出,增强凝乳强度等特性,是目前食品科学领域的研究热点之一。本研究以基础培养基M17为对照,以大豆蛋白胨、胰蛋白胨和酪蛋白胨替代M17液体培养基的复合氮源,探究不同氮源对嗜热链球菌IMAU20561胞外多糖的产量、分子质量及结构的影响。结果表明:嗜热链球菌IMAU20539以大豆蛋白胨为唯一氮源的M17培养基中胞外多糖产量达480.7 mg/L,远高于其它3种培养基所得多糖的产量。不同氮源培养基所得粗EPS经纯化后收集的EPS组分不同,各EPS组分的分子质量也有显著差异,以酪蛋白胨为唯一氮源的M17培养基所得EPS分子质量最大(5.964×105u),其次为基础培养基M17(1.260×105u)、大豆蛋白胨培养基(6.635×104u)和胰蛋白胨培养基(1.192×104u)。不同氮源培养基所得多糖结构有显著差异,大豆蛋白胨培养基所得EPS主要由半乳糖醛酸、半乳糖和阿拉伯糖组成;胰蛋白胨培养基所得EPS主要由葡萄糖醛酸、葡萄糖和半乳糖组成;酪蛋白胨培养基和基础培养基M17所得EPS有相似的单糖组成,主要由甘露糖、葡萄糖和半乳糖组成,占比分别为10.46∶1.62∶87.37和20.37∶2.77∶74.91。

具有良好风味德氏乳杆菌保加利亚亚种的筛选及其产香性能分析

风味是评价酸奶发酵剂及其产品的重要指标之一。该文以科汉森公司提供的商业发酵剂为对照组,以分离自传统发酵乳制品中具有良好发酵特性的6株德氏乳杆菌保加利亚亚种为试验菌株,从中筛选出1株具有良好风味的菌株。采用固相微萃取(solid phase micro-extraction,SPME)和GC-MS技术测定牛乳发酵终点时的挥发性风味化合物,从中筛选出1株与对照组中的挥发性风味物质的种类和相对含量相似度较高的菌株,并继续分析该菌株在牛乳发酵和贮藏期间所产风味物质的动态变化情况。德氏乳杆菌保加利亚亚种MGA17-6在牛乳发酵和贮藏期间产生的主要风味化合物包括酸类、醛类、酮类、酯类、醇类等,其中一些重要的化合物如乙酸、乙醛、庚醛、乙偶姻、1-庚醇等对发酵乳的风味产生重要的影响。筛选出1株具有良好风味的德氏乳杆菌保加利亚亚种MGA17-6。

具有良好风味嗜热链球菌的筛选及其产香特性分析

嗜热链球菌作为酸奶发酵剂的常用菌株之一,在牛乳发酵和贮藏过程中可以赋予产品优良的质地、丰富的营养价值和独特的风味。本实验在前期研究的基础上,以商业发酵剂为对照组,以分离自不同地区传统发酵乳中的具有良好发酵特性的7株嗜热链球菌为实验菌株,采用固相微萃取结合气相色谱-质谱联用技术对发酵终点,即pH4.5时发酵乳中的挥发性风味物质进行检测分析。结果表明,在所有实验菌株中,G80-2发酵乳中的挥发性风味化合物的组成及含量最接近对照组。在此基础上,对G80-2菌株在牛乳发酵和贮藏过程中所产生的挥发性风味物质进行动态分析,发现该菌株在发酵和贮藏期间检测出酸类(4种)、醇类(10种)、酮类(12种)、醛类(6种)、酯类(1种)等多种化合物,且一些主要特征风味物质如乙酸、乙醛、双乙酰、乙偶姻、2-庚酮、1-庚醇等相对含量较高,说明该菌株可作为发酵剂应用于乳制品生产中。

基于固相微萃取-气相色谱-质谱与电子鼻技术分析发酵乳中的挥发性风味物质

为筛选风味优良的发酵剂菌株。该实验在前期研究的基础上,以具有良好风味的德氏乳杆菌保加利亚亚种和嗜热链球菌为实验菌株,进行复配发酵,采用固相微萃取-气相色谱-质谱(solid phase microextraction and gas chromatography-mass spectrometry,SPME-GC-MS)等方法对复配发酵乳香气成分进行检测分析。SPME-GC-MS分析结果表明,对照菌株JD和6组复配发酵乳中共检测出116种挥发性风味物质,其中有酸类化合物(17种)、醛类化合物(11种)、酮类化合物(17种)、醇类化合物(15种)、酯类化合物(11种)、烷烃类(30种)、含氮化合物(15种)。气味活度值(odor activity values,OAV)结果表明发酵乳中关键性风味物质(OAV≥1)有6种,包括3-甲基丁醛、苯甲醛、正壬醛、双乙酰、乙偶姻和2-壬酮。而其他化合物,如辛酸、乙醛、3-羟基丁醛、庚醛、癸醛和2-庚酮等对发酵乳的整体风味起修饰作用(0. 1≤OAV <1)。其中,这些关键性风味物质在样品中浓度较高,赋予发酵乳优良风味。主成分分析及线性判别分析结果表明,A6复配组有良好产香特性,在发酵过程中产生的风味和酸类化合物、酮类化合物、醇类化合物、含氮类化合物、烷烃类化合物等呈正相关。

嗜热链球菌发酵乳中挥发性风味物质的GC-MS指纹图谱

嗜热链球菌是发酵乳生产中常用的发酵剂菌种之一。以分离自传统发酵乳制品曲拉中的1株具有良好风味的嗜热链球菌IMAU80285为试验菌株,采用气相色谱-质谱联用仪等仪器和主成分分析、相似度分析等方法,对该菌株在发酵乳制作和贮藏期间产生的风味物质进行全面、系统的分析。结果表明:在发酵乳制作和贮藏期间,从嗜热链球菌IMAU80285中共测得84种风味物质,主要包括酸类化合物(11种)、醛类化合物(13种)、酮类化合物(12种)、醇类化合物(22种)、酯类化合物(9种)、烷烃类化合物(14种)、含氮类化合物(3种)。主成分分析结果表明:关键性风味物质(OAV≥0.1)在发酵初期(发酵4,6 h)和前发酵与贮藏期间(后熟,贮藏1,2,3,7,14 d)有明显的区分,发酵初期(发酵4,6 h)和前发酵时,与乙偶姻、庚醛、1-壬醇、己酸乙酯等17种关键性风味物质(OAV≥0.1)有较强的相关性,而贮藏期间(后熟,贮藏1,2,3,7,14 d)与2,3-丁二酮、3-甲基-1-丁醇、丁酸乙酯等7种关键性风味物质(OAV≥0.1)的相关性较强;重叠色谱图及相似度分析结果表明,发酵乳中的风味物质在发酵乳制作及贮藏期间变化显著,随着贮藏时间的延长,发酵乳的风味差异明显。

不同地域嗜热链球菌在发酵乳制作中产关键性风味物质研究

以来自不同地域的6株嗜热链球菌(Streptococcus thermophilus)为实验菌株,采用固相微萃取与气相色谱-质谱联用技术(SPME-GC-MS)相结合的方法,并结合香气阈值和相对气味活度值(relative odor activity value,ROAV)探讨发酵牛乳中关键性风味物质。结果表明,6株嗜热链球菌发酵乳中共检测出63种挥发性风味物质,包括醛类、酮类、酸类、酯类、醇类、芳香族及烷烃化合物等。其中,双乙酰、乙偶姻、乙醛、2-壬酮等12种挥发性化合物的ROAV值较高(ROAV≥1),对发酵乳总体风味贡献较大。主成分分析和相似度比较分析结果表明,来自同一地域的嗜热链球菌发酵乳中风味化合物之间具有较高的相似性,而不同地域的菌株发酵乳中风味化合物之间相似度较低,说明生长环境压力能够对菌株发酵乳的产香特性产生影响。

The 2022 report of synergetic roadmap on carbon neutrality and clean air for China:Accelerating transition in key sectors

China is now confronting the intertwined challenges of air pollution and climate change.Given the high synergies between air pollution abatement and climate change mitigation,the Chinese government is actively promoting synergetic control of these two issues.The Synergetic Roadmap project was launched in 2021 to track and analyze the progress of synergetic control in China by developing and monitoring key indicators.The Synergetic Roadmap 2022 report is the first annual update,featuring 20 indicators across five aspects:synergetic governance system and practices,progress in structural transition,air pollution and associated weather-climate interactions,sources,sinks,and mitigation pathway of atmospheric composition,and health impacts and benefits of coordinated control.Compared to the comprehensive review presented in the 2021 report,the Synergetic Roadmap 2022 report places particular emphasis on progress in 2021 with highlights on actions in key sectors and the relevant milestones.These milestones include the proportion of non-fossil power generation capacity surpassing coal-fired capacity for the first time,a decline in the production of crude steel and cement after years of growth,and the surging penetration of electric vehicles.Additionally,in 2022,China issued the first national policy that synergizes abatements of pollution and carbon emissions,marking a new era for China's pollution-carbon co-control.These changes highlight China's efforts to reshape its energy,economic,and transportation structures to meet the demand for synergetic control and sustainable development.Consequently,the country has witnessed a slowdown in carbon emission growth,improved air quality,and increased health benefits in recent years.

MEIC-global-CO_(2):A new global CO_(2)emission inventory with highly-resolved source category and sub-country information

CO_(2)emission inventory provides fundamental data for climate research and emission mitigation.Currently,most global CO_(2)emission inventories were developed with energy statistics from International Energy Agency(IEA)and were available at country level with limited source categories.Here,as the first step toward a high-resolution and dynamic updated global CO_(2)emission database,we developed a data-driven approach to construct seamless and highly-resolved energy consumption data cubes for 208 countries/territories,797 sub-country administrative divisions in 29 countries,42 fuel types,and 52 sectors,with the fusion of activity data from 24 international statistics and 65 regional/local statistics.Global CO_(2)emissions from fossil fuel combustion and cement production in 1970–2021 were then estimated with highly-resolved source category(1,484 of total)and sub-country information(797 of total).Specifically,73%of global CO_(2)emissions in 2021 were estimated with sub-country information,providing considerably improved spatial resolution for global CO_(2)emission accounting.With the support of detailed information,the dynamics of global CO_(2)emissions across sectors and fuel types were presented,representing the evolution of global economy and progress of climate mitigation.Remarkable differences of sectoral contribution were found across sub-country administrative divisions within a given country,revealing the uneven distribution of energy and economic structure among different regions.Our estimates were generally consistent with existing databases at aggregated level for global total or large emitters,while large discrepancies were observed for middle and small emitters.Our database,named the Multiresolution Emission Inventory model for Climate and air pollution research(MEIC)is publicly available through http://meicmodel.org.cn with highly-resolved information and timely update,which provides an independent carbon emission accounting data source for climate research.

Optimizing air quality and health Co-benefits of mitigation technologies in China: An integrated assessment

Carbon mitigation technologies lead to air quality improvement and health co-benefits,while the practical effects of the technologies are dependent on the energy composition,technological advancements,and economic development.In China,mitigation technologies such as end-of-pipe treatment,renewable energy adoption,carbon capture and storage(CCS),and sector electrification demonstrate significant promise in meeting carbon reduction targets.However,the optimization of these technologies for maximum co-benefits remains unclear.Here,we employ an integrated assessment model(AIM/enduse,CAM-chem,IMED|HEL)to analyze air quality shifts and their corresponding health and economic impacts at the provincial level in China within the two-degree target.Our findings reveal that a combination of end-of-pipe technology,renewable energy utilization,and electrification yields the most promising results in air quality improvement,with a reduction of fine particulate matter(PM2.5)by−34.6μg m^(−3) and ozone by−18.3 ppb in 2050 compared to the reference scenario.In contrast,CCS technology demonstrates comparatively modest improvements in air quality(−9.4μg m^(−3) for PM2.5 and−2.4 ppb for ozone)and cumulative premature deaths reduction(−3.4 million from 2010 to 2050)compared to the end-of-pipe scenario.Notably,densely populated regions such as Henan,Hebei,Shandong,and Sichuan experience the most health and economic benefits.This study aims to project effective future mitigation technologies and climate policies on air quality improvement and carbon mitigation.Furthermore,it seeks to delineate detailed provincial-level air pollution control strategies,offering valuable guidance for policymakers and stakeholders in pursuing sustainable and health-conscious environmental management.

发酵乳中风味物质的研究进展

风味是评估酸奶品质的主要指标之一。乳酸菌在发酵过程中可生成多种风味化合物,主要包括醛类、酮类、酸类、酯类等化合物,这些化合物的种类和含量对发酵乳品质具有重要影响。本文综述发酵乳中的一些主要风味化合物及其性质,以及在风味化合物研究方面取得的进展。

嗜热链球菌IMAU20246胞外多糖基因簇及其表达分析

【目的】嗜热链球菌IMAU20246是一株具有良好发酵特性且高产胞外多糖(exopolysaccharides,EPS)的菌株,但其EPS基因簇及合成途径尚不清晰。因此可通过全基因组测序及生物信息学分析菌株基因组序列,探究EPS合成及调控机制。【方法】本实验对嗜热链球菌IMAU20246进行全基因组测序并进行生物信息学分析,解析EPS生物合成相关基因簇及EPS合成途径,同时采用实时荧光定量PCR技术(quantitative real-time PCR,qRT-PCR)对其不同时间点EPS基因簇的表达进行定量分析。【结果】嗜热链球菌IMAU20246基因组中有一个18.1 kb的EPS生物合成基因簇,编码15个与EPS生物合成相关的基因。嗜热链球菌IMAU20246通过转运葡萄糖、甘露糖、果糖、半乳糖、乳糖、海藻糖、纤维二糖及蔗糖合成UDP-葡萄糖、dTDP-葡萄糖、dTDP-鼠李糖、UDP-半乳糖、UDP-呋喃半乳糖、UDP-N-乙酰葡萄糖胺和UDP-N-乙酰半乳糖胺等7种糖核苷酸。qRT-PCR的结果表明,EPS基因簇中的基因在细胞生长阶段均能表达,特别是糖基转移酶基因epsE、epsF、epsH和epsJ在培养6 h时表达量最高,此时EPS产量达到最高。【结论】本研究从基因组解析了嗜热链球菌IMAU20246 EPS基因簇及其合成途径,为菌株的进一步开发提供了理论依据。

Air pollution characteristics and their relationship with emissions and meteorology in the Yangtze River Delta region during 2014–2016

With rapid economic growth and urbanization, the Yangtze River Delta(YRD) region in China has experienced serious air pollution challenges. In this study, we analyzed the air pollution characteristics and their relationship with emissions and meteorology in the YRD region during 2014–2016. In recent years, the concentrations of all air pollutants, except O3,decreased. Spatially, the PM2.5, PM10, SO2, and CO concentrations were higher in the northern YRD region, and NO2 and O3 were higher in the central YRD region. Based on the number of non-attainment days(i.e., days with air quality index greater than 100), PM2.5 was the largest contributor to air pollution in the YRD region, followed by O3, PM10, and NO2.However, particulate matter pollution has declined gradually, while O3 pollution worsened.Meteorological conditions mainly influenced day-to-day variations in pollutant concentrations. PM2.5 concentration was inversely related to wind speed, while O3 concentration was positively correlated with temperature and negatively correlated with relative humidity.The air quality improvement in recent years was mainly attributed to emission reductions.During 2014–2016, PM2.5, PM10, SO2, NOx, CO, NH3, and volatile organic compound(VOC)emissions in the YRD region were reduced by 26.3%, 29.2%, 32.4%, 8.1%, 15.9%, 4.5%, and0.3%, respectively. Regional transport also contributed to the air pollution. During regional haze periods, pollutants from North China and East China aggravated the pollution in the YRD region. Our findings suggest that emission reduction and regional joint prevention and control helped to improve the air quality in the YRD region.

Rapid improvement of PM2.5 pollution and associated health benefits in China during 2013–2017

Exposure to fine particulate matter(PM2.5)is known to harm public health.In China,after implementation of aggressive emissions control measures under the Action Plan of Air Pollution Prevention and Control(2013-2017),air quality has significantly improved.In this work,we investigated changes in PM2.5 exposure and the associated health impacts in China for the period 2013-2017.We used an optimal estimator of PM2.5 combining in-situ observations,satellite measurements,and simulations from a chemical transport model to derive the spatial and temporal variations in PM2.5 exposure,and then used welldeveloped exposure-response functions to estimate the premature deaths attributable to PM2.5 exposure.We found that national population-weighed annual mean PM2.5 concentrations decreased from 67.4μgm-3 in 2013 to 45.5μgm-3 in 2017(32%reduction).This rapid decrease in PM2.5 pollution led to a 14%reduction in premature deaths due to long-term exposure.We estimated that,during 2013-2017,the premature deaths attributable to long-term PM2.5 exposure decreased from 1.2 million(95%CI:1.0,1.3;fraction of total mortality:13%)in 2013 to 1.0 million(95%CI:0.9,1.2;10%)in 2017.Despite the rapid decrease in annual mean PM2.5 concentrations,health benefits associated with reduced long-term exposure were limited,because for many cities,the PM2.5 levels remain at the portion where the exposure-response function is less steeper than that at the lowconcentration end.We also found that the deaths associated with acute exposure decreased by 61%during 2013-2017 due to rapid reduction in the number of heavily polluted days.Our results confirm that clean air policies in China have mitigated the air pollution crisis;however,continuous emissions reduction efforts are required to protect citizens from air pollution.

Impact of China’s Air Pollution Prevention and Control Action Plan on PM2.5 chemical composition over eastern China

China promulgated the Air Pollution Prevention and Control Action Plan(the Action Plan)in 2013 and developed stringent control measures to mitigate fine particulate matter(PM2.5) pollution.Here,we investigated the PM2.5 chemical composition changes over eastern China associated with the Action Plan during 2013-2017 using satellite-based PM2.5 chemical composition data derived using CMAQ simulations and satellite inputs.The PM2.5 concentrations decreased considerably during this time as a result of the reductions in all chemical species in PM2.5.The population-weighted mean concentrations over eastern China decreased from 11.1 to 6.7μgm-3 for SO42-,13.8-13.1μgm-3 for NO3-,7.4-5.8μgm-3 for NH4+,9.9-8.4μgm-3 for OM,4.6-3.8μg m-3 for BC and 12.9-9.6μg m-3 for other species in PM2.5.SO42-had the largest reduction of 40%,while NO3-had the lowest reduction of 5%,resulting in a greater fraction of NO3-and a smaller fraction of SO42-in PM2.5.Among the three key regions,Beijing-Tianjin-Hebei had the largest reduction in PM2.5 and its chemical compositions.The decrease in SO42-concentrations was in line with the reduction of SO2 emissions,and the major driver of the SO2 emission reductions was the industrial sector.The decrease in NO3 concentrations was limited because the decrease in SO2 emissions and the stable NH3 emissions facilitated the formation of NO3-from HNO3,which partially offset the reduction in NOx emissions driven by the power sector.To mitigate PM2.5 pollution more effectively,future efforts are needed to reduce NH3 emissions.

China’s carbon neutrality:an extensive and profound systemic reform

China is the largest developing economy and carbon dioxide emitter in the world,the carbon neutrality goal of which will have a profound influence on the mitigation pathway of global climate change.The transition towards a carbon-neutral society is integrated into the construction of ecological civilization in China,and brings profound implications for China’s socioeconomic development.Here,we not only summarize the major challenges in achieving carbon neutrality in China,but also identify the four potential new opportunities:namely,the acceleration of technology innovations,narrowing regional disparity by reshaping the value of resources,transforming the industrial structure,and co-benefits of pollution and carbon mitigation.Finally,we provide five policy suggestions and highlight the importance of balancing economic growth and carbon mitigation,and the joint efforts among the government,the enterprises,and the residents.

Synergetic roadmap of carbon neutrality and clean air for China

It is well recognized that carbon dioxide and air pollutants share similar emission sources so that synergetic policies on climate change mitigation and air pollution control can lead to remarkable co-benefits on greenhouse gas reduction,air quality improvement,and improved health.In the context of carbon peak,carbon neutrality,and clean air policies,this perspective tracks and analyzes the process of the synergetic governance of air pollution and climate change in China by developing and monitoring 18 indicators.The 18 indicators cover the following five aspects:air pollution and associated weather-climate conditions,progress in structural transition,sources,inks,and mitigation pathway of atmospheric composition,health impacts and benefits of coordinated control,and synergetic governance system and practices.By tracking the progress in each indicator,this perspective presents the major accomplishment of coordinated control,identifies the emerging challenges toward the synergetic governance,and provides policy recommendations for designing a synergetic roadmap of Carbon Neutrality and Clean Air for China.

Contact-dependent delivery of IL-2 by dendritic cells to CD4 T cells in the contraction phase promotes their long-term survival

Common y chain cytokines are important for immune memory formation.Among them,the role of IL-2 remains to be fully explored.It has been suggested that this cytokine is critically needed in the late phase of primary CD4 T cell activation.Lack of IL-2 at this stage sets for a diminished recall response in subsequent challenges.However,as IL-2 peak production is over at this point,the source and the exact mechanism that promotes its production remain elusive.We report here that resting,previously antigen-stimulated CD4 T cells maintain a minimalist response to dendritic cells after their peak activation in vitro.This subtle activation event may be induced by DCs without overt presence of antigen and appears to be stronger if IL-2 comes from the same dendritic cells.This encounter reactivates a miniature IL-2 production and leads a gene expression profile change in these previously activated CD4 T cells.The CD4 T cells so experienced show enhanced reactivation intensity upon secondary challenges later on.Although mostly relying on in vitro evidence,our work may implicate a subtle programing for CD4 T cell survival after primary activation in vivo.