Migration of Plasmodium sporozoites through cells before infection

Intracellular bacteria and parasites typically invade host cells through the formation of an internalization vacuole around the invading pathogen. Plasmodium sporozoites, the infective stage of the malaria parasite transmitted by mosquitoes, have an alternative mechanism to enter cells. We observed breaching of the plasma membrane of the host cell followed by rapid repair. This mode of entry did not result in the formation of a vacuole around the sporozoite, and was followed by exit of the parasite from the host cell. Sporozoites traversed the cytosol of several cells before invading a hepatocyte by formation of a parasitophorous vacuole, in which they developed into the next infective stage. Sporozoite migration through several cells in the mammalian host appears to be essential for the completion of the life cycle.     

Manipulation of host hepatocytes by the malaria parasite for delivery into liver sinusoids

The merozoite stage of the malaria parasite that infects erythrocytes and causes the symptoms of the disease is initially formed inside host hepatocytes. However, the mechanism by which hepatic merozoites reach blood vessels (sinusoids) in the liver and escape the host immune system before invading erythrocytes remains unknown. Here, we show that parasites induce the death and the detachment of their host hepatocytes, followed by the budding of parasite-filled vesicles (merosomes) into the sinusoid lumen. Parasites simultaneously inhibit the exposure of phosphatidylserine on the outer leaflet of host plasma membranes, which act as "eat me" signals to phagocytes. Thus, the hepatocyte-derived merosomes appear to ensure both the migration of parasites into the bloodstream and their protection from host immunity.     

A role for the protease falcipain 1 in host cell invasion by the human malaria parasite

Cysteine proteases of Plasmodium falciparum are required for survival of the malaria parasite, yet their specific cellular functions remain unclear. We used a chemical proteomic screen with a small-molecule probe to characterize the predominant cysteine proteases throughout the parasite life cycle. Only one protease, falcipain 1, was active during the invasive merozoite stage. Falcipain 1-specific inhibitors, identified by screening of chemical libraries, blocked parasite invasion of host erythrocytes, yet had no effect on normal parasite processes such as hemoglobin degradation. These results demonstrate a specific role for falcipain 1 in host cell invasion and establish a potential new target for antimalarial therapeutics.     

Host cell invasion by apicomplexan parasites: insights from the co-structure of AMA1 with a RON2 peptide

Apicomplexan parasites such as Toxoplasma gondii and Plasmodium species actively invade host cells through a moving junction (MJ) complex assembled at the parasite-host cell interface. MJ assembly is initiated by injection of parasite rhoptry neck proteins (RONs) into the host cell, where RON2 spans the membrane and functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. We have determined the structure of TgAMA1 complexed with a RON2 peptide at 1.95 angstrom resolution. A stepwise assembly mechanism results in an extensive buried surface area, enabling the MJ complex to resist the mechanical forces encountered during host cell invasion. Besides providing insights into host cell invasion by apicomplexan parasites, the structure offers a basis for designing therapeutics targeting these global pathogens.     

Chemical Usurpation of a Nest by Paper Wasp Parasites

The paper wasp Polistes atrimandibularis is an obligatory social parasite of another Polistes species, P. biglumis bimaculatus. To control the host nest, the parasite sequentially changes the composition of its chemical signature, the cuticular hydrocarbons, during the colonial cycle. Gas chromatography-mass spectrometry of the cuticular hydrocarbons at every stage of the cycle showed that the parasite can switch on and off an entire chemical family, namely, the unsaturated hydrocarbons. In this way the parasite can match the host signature at a critical moment of the colonial cycle.     

八角茴香水提物调控宿主免疫反应抗石斑鱼虹彩病毒的机制研究

【目的】从免疫应答角度探析八角茴香（Illicium verum Hook.f.）水提物（IVE）调控宿主免疫反应而发挥抗石斑鱼虹彩病毒（SGIV）的作用机制,为八角茴香应用于石斑鱼健康养殖产业及开发绿色、健康、高效渔用药物提供理论依据。【方法】通过光学显微镜观察及CCK-8细胞活力测定确定IVE的细胞安全工作浓度,利用实时荧光定量PCR检测IVE对宿主细胞干扰素相关基因（IFN、STAT1、PKR、ISG15、KK_α、STING和IRF3）表达的影响,并以光学显微镜观察和实时荧光定量PCR分析IVE在细胞水平抗SGIV的效果,通过石斑鱼活体试验进一步验证IVE的抗SGIV效果。【结果】IVE细胞水平的安全工作浓度≤0.50 mg/mL; IVE预处理GS细胞2 h可显著（P<0.05,下同）或极显著（P<0.01,下同）激活干扰素相关基因（IFN、STAT1、PKR、IKK_α、IRF3和STING）的表达。SGIV感染GS细胞24和48 h时,经IVE预处理的细胞病变效应（CPEs）明显少于未使用IVE预处理的GS细胞,且细胞内SGIV的MCP基因相对表达量极显著降低,表明IVE可有效抑制SGIV感染;此外,IVE可增强SGIV感染GS细胞中干扰素相关基因的表达,具体表现为IFN、STAT1和IRF3基因在病毒感染后24 h极显著上调,PKR、IKK_α、ISG15和STING基因在病毒感染后24和48 h呈显著或极显著上调趋势。在石斑鱼活体试验中,IVE与SGIV混合腹腔注射后石斑鱼脾脏中SGIV的MCP基因相对表达量在病毒感染后24和48 h均极显著低于仅注射SGIV的石斑鱼。【结论】IVE具有抑制SGIV感染的功能,其作用机制可能是通过诱导干扰素相关基因表达而激活宿主的抗病毒状态,从而发挥间接抗SGIV效果;也说明八角茴香在水产疫病防控中具有研发成渔用抗病功能制剂的潜力。     

A haptoglobin-hemoglobin receptor conveys innate immunity to Trypanosoma brucei in humans

The protozoan parasite Trypanosoma brucei is lysed by apolipoprotein L-I, a component of human high-density lipoprotein (HDL) particles that are also characterized by the presence of haptoglobin-related protein. We report that this process is mediated by a parasite glycoprotein receptor, which binds the haptoglobin-hemoglobin complex with high affinity for the uptake and incorporation of heme into intracellular hemoproteins. In mice, this receptor was required for optimal parasite growth and the resistance of parasites to the oxidative burst by host macrophages. In humans, the trypanosome receptor also recognized the complex between hemoglobin and haptoglobin-related protein, which explains its ability to capture trypanolytic HDLs. Thus, in humans the presence of haptoglobin-related protein has diverted the function of the trypanosome haptoglobin-hemoglobin receptor to elicit innate host immunity against the parasite.     

二化螟绒茧蜂过寄生现象的初步研究

在室内通过对二化螟绒茧蜂过寄生现象的研究发现,二化螟绒茧蜂的蜂体大小与寄主体内寄生蜂数量呈线性负相关。而寄主育出蜂量与寄主体长呈线性正相关。一头寄主可被二化螟绒茧蜂多次产卵寄生,被产卵1～2次的寄主能正常育出绒茧蜂,且体内很少残留不能正常发育的二化螟绒茧蜂卵和幼虫,而被产卵3次以上的寄主死亡率高,即使存活,也只有部分二化螟绒茧蜂能正常钻出寄主,多数蜂幼虫和卵不能正常发育而死亡。当二化螟绒茧蜂在不同间隔时间内对寄主进行2次产卵寄生吋,均可育出正常后代,但第二次产下的蜂后代因种内竞争失败而不能正常生长发育。     

桔潜蛾姬小蜂Elachertus sp.对桔潜蛾幼虫寄生模型的初步研究

根据田间调查材料,分别以 Holling 圆盘方程、Hassell 和 Varley 模型及 Hassell 和 Roger 模型分析了桔潜蛾姬小蜂对寄主密度的功能反应,对自身密度的功能反应以及对寄主密度,自身密度的共同反应.模拟结果,各参数如下:瞬时攻击率 a=0.1242处理时间 Th=0.1316寄生上限 Na’(∞)=7.6搜索常数 Q=0.5226相互干扰常数 m=0.8126与国内外报导的资料比较,上述参数基本上符合天敌的理想属性,从理论上证明桔潜蛾姬小蜂是有保护利用前途的寄生昆虫。     

蜂密度和寄主卵密度对玉米螟赤眼蜂寄生效能的影响

在实验室内以米蛾卵作寄主研究了蜂密度和寄主密度对玉米螟赤眼蜂寄生效能的影响。在第一个试验中,1、2、4和8头1日龄的玉米螟赤眼蜂雌蜂被分别接入400粒米蛾卵上,结果表明,卵的总寄生率在最高蜂密度(8头)时显著高于其他蜂密度,但平均每头雌蜂的寄生率却随蜂密度的增加而减少,当蜂密度从1增加到8头时,平均每头雌蜂的寄生率几乎减少了近一半,同时每雌产后代数也随蜂密度的增加而减少,说明蜂密度的增加降低了玉米螟赤眼蜂的寄生效能．另一试验中,50、100、200和400粒米蛾卵上分别接入1头1日龄的赤眼蜂雌蜂,结果表明,随寄主卵密度的增加,卵的总寄生率也显著增加,寄主卵密度每增加1梯度,每雌产后代数平均增加了2倍,由此可以看出,寄主卵密度的增加对玉米螟赤眼蜂的寄生效能有增强作用。     

A secreted serine-threonine kinase determines virulence in the eukaryotic pathogen Toxoplasma gondii

Toxoplasma gondii strains differ dramatically in virulence despite being genetically very similar. Genetic mapping revealed two closely adjacent quantitative trait loci on parasite chromosome VIIa that control the extreme virulence of the type I lineage. Positional cloning identified the candidate virulence gene ROP18, a highly polymorphic serine-threonine kinase that was secreted into the host cell during parasite invasion. Transfection of the virulent ROP18 allele into a nonpathogenic type III strain increased growth and enhanced mortality by 4 to 5 logs. These attributes of ROP18 required kinase activity, which revealed that secretion of effectors is a major component of parasite virulence.     

枯叶蛾平腹小蜂(Anastatus sp.)生物学特性的观察

枯叶蛾平腹小蜂是马尾松毛虫卵寄生蜂的优势种类。在林内一年可发生2—4代,室内可繁殖六代,以预蛹在寄主卵内越冬,次年四月中、下旬开始羽化。在寄主卵内发育历期为18—22天,各虫态历期为;卵2—3天,幼虫(包括预蛹)7—8天,蛹9—11天。每一寄主卵内只可发育出一头蜂。雌蜂寿命在给食时平均为47.3天。野外调查雌雄性比为1.27:1;室内繁蜂以柞蚕卵作为寄主则雌性有增高的现象。室内小群体繁蜂的平均产卵量为:越冬代36.5粒,第一代67.9粒,第二代52.3粒。以柞蚕作寄主雌蜂产卵量较高,繁蜂群体增大时,产卵量和日产卵量均有下降趋势。经测算,在卵内发育起点和有效积温分别为14.7℃和242.5日度。     

Malaria parasites adopt host cell superoxide dismutase

Aerobic organisms depend on superoxide dismutase to suppress the formation of dangerous species of activated oxygen. Intraerythrocytic stages of the malaria parasite exist within a highly aerobic environment and cause the generation of increased amounts of activated oxygen. Plasmodium berghei in mice was found to derive a substantial amount of superoxide dismutase activity from the host cell cytoplasm. Plasmodia isolated from mouse red cells contained mouse superoxide dismutase, whereas rat-derived parasites contained the rat enzyme. This is believed to be the first example of the acquisition of a host cell enzyme by an intracellular parasite.     

Quinacrine: mechanisms of antimalarial action

Two new interesting modes of action of quinacrine have been discovered. The first concerns a dose-related inhibition of uptake of [8-(3)H] adenosine into host cells of parasitized blood. Second, the drug inhibits the incorporation of tritiated adenosine triphosphate primarily into RNA but also into DNA of the erythrocyte-free malarial parasite Plasmodium berghei.     

蚜虫的重寄生蜂研究 I、白木细蜂属Dendrocecrus的中国种新记录(Hym.Megaspilidae)

本文报道分布于我国、寄生于蚜茧蜂的大痣细蜂科Megaspilidae白木细蜂属Dendrocerus的3种蚜虫的重寄生蜂。文中列有分种检索表,形态描述、特征图、生物学记述、重寄生的寄主和初寄生蜂的寄主蚜虫。其中合沟细蜂Dendrocerus carpenteri Curtis和粗脊细蜂Dendrocerus laevis(Ratzeburg)为中国分布的新记录。蚜虫初寄生蜂经常被各类群重寄生蜂寄生,导致田间后期初寄生蜂虫口下降,影响蚜茧蜂控制蚜虫的效果。白木细蜂属仅产卵于僵蚜内的蚜茧蜂的老熟幼虫或蛹期,该蜂产卵于僵蚜内初寄生幼虫的体表,属外寄生的重寄生蜂。该蜂在福建6月份的自然条件下,从卵到成蜂羽化的历期为15～17天。     

Vaccines. Searching for a parasite's weak spot

Using a host of new technologies, vaccine developers are trying to target the malaria parasite at every stage of its complex life cycle. Researchers now predict that within 5 or 10 years they will have a successful vaccine that will actually save lives. But in malaria vaccine research, the concept of "success" comes with caveats.     

烟蚜茧蜂生物学研究Ⅳ．──繁殖力、内禀增长力、功能反应及对桃蚜的抑制作用

在恒定的实验室条件下测定了寄生于桃蚜２～３龄若虫的烟蚜茧蜂的繁殖力和寿命。在２２℃下在寄主密度分别为５，１０，２５，１００或２００头／ｄ蚜虫时，寄生蜂平均寿命为３．６～６．８ｄ。试验证明雌蜂产卵量及寄生蚜虫数量为随寄主密度的增加而呈负加速上升，但当密度高于５０头／ｄ蚜虫时，两者均不再明显上升。分析证明烟蚜茧峰的内禀增长力随寄主密度增加而增加，在密度为２００头／ｄ蚜虫时达到最大值，为０．３６４１。当供蚜密度从５增加到２００时烟蚜茧蜂的净生殖力增加了１８倍，但平均世代长度则不受影响。烟蚜茧蜂对桃蚜的功能反应属于ＨｏｌｌｉｎｇⅡ型反应，经计算其ａ＝６．０３４１，Ｔｈ＝０．０１４。此外，还在７个不同起始密度下测定了烟蚜茧蜂对桃蚜种群的抑制作用。     

Genome sequence of Theileria parva, a bovine pathogen that transforms lymphocytes

We report the genome sequence of Theileria parva, an apicomplexan pathogen causing economic losses to smallholder farmers in Africa. The parasite chromosomes exhibit limited conservation of gene synteny with Plasmodium falciparum, and its plastid-like genome represents the first example where all apicoplast genes are encoded on one DNA strand. We tentatively identify proteins that facilitate parasite segregation during host cell cytokinesis and contribute to persistent infection of transformed host cells. Several biosynthetic pathways are incomplete or absent, suggesting substantial metabolic dependence on the host cell. One protein family that may generate parasite antigenic diversity is not telomere-associated.