Studies on the Persistent Infection with Measles Virus in HeLa Cells

HeLa/MV cells which have previously been found to contain measles antigen in more than 90% of cells were very similar to normal HeLa cells in their morphology and growth. Although almost all of HeLa/MV cells may be infected, only 10% of them released infectious virus particles. The hemadsorption test, however, showed that most of the infected cells produced by hemagglutinin. Two kinds of clones were obtained by cloning HeLa/MV cells in the presence of anti-measles serum. One was the virus-releasing clone and the other the uninfected clone which did not contain any measles antigen. The proportions of virus-releasing clones to all clones varied between 20 to 54%, and did not show any increase even after recloning of the virus-releasing clones. The susceptibility of the uninfected clones to the standard measles virus was not different from that of normal HeLa cells.     

The larger attachment glycoprotein of respiratory syncytial virus produced in primary human bronchial epithelial cultures reduces infectivity for cell lines

Respiratory syncytial virus (RSV) infects the upper and lower respiratory tracts and can cause lower respiratory tract infections in children and elders. RSV has traditionally been isolated, grown, studied and quantified in immortalized cell lines, most frequently HEp-2 cells. However, in vivo RSV infection is modeled more accurately in primary well differentiated human bronchial epithelial (HBE) cultures where RSV targets the ciliated cells and where the putative RSV receptor differs from the receptor on HEp-2 cells. The RSV attachment (G) glycoprotein in virions produced by HEp-2 cells is a highly glycosylated 95 kDa protein with a 32 kDa peptide core. However, virions produced in HBE cultures, RSV (HBE), contain an even larger, 170 kDa, G protein (LgG). Here we show that LgG is found in virions from both subgroups A and B lab-adapted and clinical isolates. Unexpectedly, RSV (HBE) virions were approximately 100-fold more infectious for HBE cultures than for HEp-2 cells. Surprisingly, the cause of this differential infectivity, was reduced infectivity of RSV (HBE) on HEp-2 cells rather than enhanced infectivity on HBE cultures. The lower infectivity of RSV(HBE) for HEp-2 cells is caused by the reduced ability of LgG to interact with heparan sulfate proteoglycans (HSPG), the RSV receptor on HEp-2 cells. The discovery of different infectivity corresponding with the larger form of the RSV attachment protein when produced by HBE cultures highlights the importance of studying a virus produced by its native host cell and the potential impact on quantifying virus infectivity on cell lines where the virus entry mechanisms differ from their natural target cell.     

Recombinant measles viruses efficiently entering cells through targeted receptors

We sought proof of principle that one of the safest human vaccines, measles virus Edmonston B (MV-Edm), can be genetically modified to allow entry via cell surface molecules other than its receptor CD46. Hybrid proteins consisting of the epidermal growth factor (EGF) or the insulin-like growth factor 1 (IGF1) linked to the extracellular (carboxyl) terminus of the MV-Edm attachment protein hemagglutinin (H) were produced. The standard H protein gene was replaced by one coding for H/EGF or H/IGF1 in cDNA copies of the MV genome. Recombinant viruses were rescued and replicated to titers approaching those of the parental strain. MV displaying EGF or IGF1 efficiently entered CD46-negative rodent cells expressing the human EGF or the IGF1 receptor, respectively, and the EGF virus caused extensive syncytium formation and cell death. Taking advantage of a factor Xa protease recognition site engineered in the hybrid H proteins, the displayed domain was cleaved off from virus particles, and specific entry in rodent cells was abrogated. These studies prove that MV can be engineered to selectively eliminate cells expressing a targeted receptor and provide insights into the mechanism of MV entry.     

Engineered serine protease inhibitor prevents furin-catalyzed activation of the fusion glycoprotein and production of infectious measles virus.

We have identified the major cellular endoprotease that activates the fusion (F) glycoprotein of measles virus (MV) and have engineered a serine protease inhibitor (serpin) to target the endoprotease and inhibit the production of infectious MV. The F-protein precursor of MV was not cleaved efficiently into the mature F protein in human colon carcinoma cells lacking functional furin, indicating that furin is the major enzyme responsible for activation of the MV F protein. A human serpin alpha 1-antitrypsin variant was engineered to specifically inhibit furin. When expressed from a recombinant vaccinia virus in primate cells infected by MV, the engineered serpin (alpha 1-PDX) specifically inhibited furin-catalyzed cleavage of the F-protein precursor without affecting synthesis of other MV proteins. We generated human glioma cells stably expressing alpha 1-PDX. MV infection in these cells did not result in syncytia. The infected cells produced all the MV proteins, but the F-protein precursor remained largely uncleaved. This did not prevent virus assembly. However, the released virions contained inactive F-protein precursor rather than mature F protein, and infectious-virus titers were reduced by 3 to 4 orders of magnitude. These results show that a mature F protein is not required for the assembly of MV but is crucial for virus infectivity. The engineered serpin may offer a novel molecular antiviral approach against MV.     

Infection of human peripheral blood mononuclear cells with a temperature-sensitive mutant of measles virus.

A stable temperature-sensitive mutant of measles virus (MV ts38) was used to study the mechanism of virus-mediated immune suppression of peripheral blood mononuclear cells in vitro. Both unstimulated and phytohemagglutinin-stimulated cultures released infectious virus at 32 degrees C, whereas no virus was released at 37 degrees C, although both viral RNA and viral proteins were synthesized. However, the response of the lymphoid cells to phytohemagglutinin, concanavalin A, and herpes simplex virus antigen was decreased in the presence of MV ts38 at 37 degrees C. The viability of infected cells was not diminished, therefore excluding cell death as a reason for immunosuppression. Interleukin 2 did not play a role in the inhibitory effect of MV ts38. Antibodies to alpha interferon partially reversed the inhibitory effect of the virus infection on lymphocyte mitogenesis, thus implying that alpha interferon plays a role in the immunosuppression. Depletion experiments indicated that adherent cells play a greater role in the measles virus-induced immunosuppression than nonadherent cells. However, monocyte maturation to macrophages had no effect on the degree of immunosuppression.     

Herpes simplex virus type 1 glycoprotein K is not essential for infectious virus production in actively replicating cells but is required for efficient envelopment and translocation of infectious virions from the cytoplasm to the extracellular space.

We characterized the glycoprotein K (gK)-null herpes simplex virus type 1 [HSV-1] (KOS) delta gK and compared it to the gK-null virus HSV-1 F-gKbeta (L. Hutchinson et al., J. Virol. 69:5401-5413, 1995). delta gK and F-gKbeta mutant viruses produced small plaques on Vero cell monolayers at 48 h postinfection. F-gKbeta caused extensive fusion of 143TK cells that was sensitive to melittin, a specific inhibitor of gK-induced cell fusion, while delta gK virus did not fuse 143TK cells. A recombinant plasmid containing the truncated gK gene specified by F-gKbeta failed to rescue the ICP27-null virus KOS (d27-1), while a plasmid with the delta gK deletion rescued the d27-1 virus efficiently. delta gK virus yield was approximately 100,000-fold lower in stationary cells than in actively replicating Vero cells. The plaquing efficiencies of delta gK and F-gKbeta virus stocks on VK302 cells were similar, while the plaquing efficiency of F-gKbeta virus stocks on Vero cells was reduced nearly 10,000-fold in comparison to that of delta gK virus. Mutant delta gK and F-gKbeta infectious virions accumulated within Vero and HEp-2 cells but failed to translocate to extracellular spaces. delta gK capsids accumulated in the nuclei of Vero but not HEp-2 cells. Enveloped delta gK virions were visualized in the cytoplasms of both Vero and HEp-2 cells, and viral capsids were found in the cytoplasm of HEp-2 cells within vesicles. Glycoproteins B, C, D, and H were expressed on the surface of delta gK-infected Vero cells in amounts similar to those for KOS-infected Vero cells. These results indicate that gK is involved in nucleocapsid envelopment, and more importantly in the translocation of infectious virions from the cytoplasm to the extracellular spaces, and that actively replicating cells can partially compensate for the envelopment but not for the cellular egress deficiency of the delta gK virus. Comparison of delta gK and F-gKbeta viruses suggests that the inefficient viral replication and plaquing efficiency of F-gKbeta virus in Vero cells and its syncytial phenotype in 143TK- cells are most likely due to expression of a truncated gK.     

Tyrosine phosphorylation of measles virus nucleocapsid protein in persistently infected neuroblastoma cells.

Subacute sclerosing panencephalitis is a slowly progressing fatal human disease of the central nervous system which is a delayed sequel of measles virus (MV) infection. A typical pathological feature of this disease is the presence of viral ribonucleocapsid structures in the form of inclusion bodies and the absence of infectious virus or budding viral particles. The mechanisms governing the establishment and maintenance of a persistent MV infection in brain cells are still largely unknown. To understand the mechanisms underlying MV persistence in neuronal cells, a tissue culture model was studied. Clone NS20Y/MS of the murine neuroblastoma C1300 persistently infected with the wild-type Edmonston strain of MV secretes relatively high levels of alpha/beta interferon (IFN). As shown previously, treatment of the persistently infected cultures with anti-IFN serum converted the persistent state into a productive infection indicated by the appearance of multinucleated giant cells. In this study, we have investigated whether alpha/beta IFN produced by NS20Y/MS cells activates cellular protein tyrosine kinases which will induce tyrosine phosphorylating activity specific to virus-infected cells. We present data to show augmented protein tyrosine kinase activity in the persistently infected cells. We demonstrate that the MV N protein is phosphorylated on tyrosine in addition to serine and threonine in the persistent state but not in NS20Y cells acutely infected with MV.     

Measles virus assembly within membrane rafts

During measles virus (MV) replication, approximately half of the internal M and N proteins, together with envelope H and F glycoproteins, are selectively enriched in microdomains rich in cholesterol and sphingolipids called membrane rafts. Rafts isolated from MV-infected cells after cold Triton X-100 solubilization and flotation in a sucrose gradient contain all MV components and are infectious. Furthermore, the H and F glycoproteins from released virus are also partly in membrane rafts (S. N. Manié et al., J. Virol. 74:305-311, 2000). When expressed alone, the M but not N protein shows a low partitioning (around 10%) into rafts; this distribution is unchanged when all of the internal proteins, M, N, P, and L, are coexpressed. After infection with MGV, a chimeric MV where both H and F proteins have been replaced by vesicular stomatitis virus G protein, both the M and N proteins were found enriched in membrane rafts, whereas the G protein was not. These data suggest that assembly of internal MV proteins into rafts requires the presence of the MV genome. The F but not H glycoprotein has the intrinsic ability to be localized in rafts. When coexpressed with F, the H glycoprotein is dragged into the rafts. This is not observed following coexpression of either the M or N protein. We propose a model for MV assembly into membrane rafts where the virus envelope and the ribonucleoparticle colocalize and associate.     

Measles virus-substance P receptor interactions: Jurkat lymphocytes transfected with substance P receptor cDNA enhance measles virus fusion and replication

1. We have demonstrated previously (Harrowe et al., 1990), using a lymphoblastoid cell line that constitutively expresses the substance P receptor (SPR) (Payan et al., 1984, 1986), that this receptor may facilitate measles virus (MV) fusion with these cells. In order to test this hypothesis further, a stable cell line transfected with SPR cDNA has been established, and various stages of MV infection in SPR positive and negative cells compared. 2. Jurkat cells, a human T-lymphoblastoid cell line, were transfected with a cDNA clone encoding the SPR. Cells transfected with only the plasmid were used as controls. Jurkat cells and Jurkat vector control cells (J-vo) failed to demonstrate any detectable 125I-SP binding, whereas a clonally selected population of cells transfected with SPR cDNA (J-SPR) expressed about 50,000 receptors/cell (Sudduth-Klinger et al., 1992). 3. Using the J-vo- and J-SPR-transfected cell lines, the following experiments were conducted to investigate the effect of SPR expression on MV infection. To determine if MV would preferentially attach to J-SPR as compared to J-vo, we absorbed virus to cells at 37 degrees C for various times and measured bound MV using a fluorescence activated cell sorter (FACS). Using this approach, we found that MV bound to a greater degree to J-SPR compared with J-vo. In addition to equilibrium being reached faster for J-SPR, the total amount of bound MV was higher on J-SPR. The effect was greater at lower MOIs, suggesting that there existed multiple binding sites for MV on these cells and that the affinity is higher for those cells expressing the SPR. 4. Since binding does not necessitate a successful viral infection, we needed to know if this difference in binding reflected a difference in infection. This was demonstrated by showing an approximate twofold increase in infected cells after a 2-hr binding period with J-SPR as compared to J-vo at an MOI of 1 in an infectious cell-center assay. Moreover, when both cells types were subjected to continuous infection in culture, J-SPR-infected cells produced a seven- to ninefold increase in measles viral titer in 24 hr as compared with J-vo. The observed increase in viral titer may have resulted in more of the J-SPR cells binding virus, as indicated by our binding and infectious cell-center data, or alternatively, the virus might have entered the J-SPR cells faster and begun replication before the J-vo-infected cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Adaptation of Wild-Type Measles Virus to Tissue Culture

Measles has a host range restricted to humans and monkeys in captivity. Fresh measles virus (MV) isolates replicate readily in several human and simian B-cell lines but need a period of adaptation to other types of cells. The identification of CD46 and CD150 (SLAM) as cellular receptors for MV has helped to clarify certain aspects of the immunobiology of MV infections. We have examined the properties of an MV wild-type strain grown in the epithelial cell line Vero. After adaptation, this virus expressed high levels of both the viral glycoproteins (hemagglutinin and fusion protein) but did not induce fusion (syncytia). No changes in the amino acid sequence were found in either of the viral glycoproteins. Using several approaches, the Vero-adapted virus could not be shown to interact with CD46 either in the initiation or during the course of infection. The presence of human SLAM expressed in the Vero cells rapidly gave rise to fusion and lower yields of infectious virus.     

Human membrane cofactor protein (CD46) acts as a cellular receptor for measles virus.

A monoclonal antibody (MCI20.6) which inhibited measles virus (MV) binding to host cells was previously used to characterize a 57- to 67-kDa cell surface glycoprotein as a potential MV receptor. In the present work, this glycoprotein (gp57/67) was immunopurified, and N-terminal amino acid sequencing identified it as human membrane cofactor protein (CD46), a member of the regulators of complement activation gene cluster. Transfection of nonpermissive murine cells with a recombinant expression vector containing CD46 cDNA conferred three major properties expected of cells permissive to MV infection. First, expression of CD46 enabled MV to bind to murine cells. Second, the CD46-expressing murine cells were able to undergo cell-cell fusion when both MV hemagglutinin and MV fusion glycoproteins were expressed after infection with a vaccinia virus recombinant encoding both MV glycoproteins. Third, M12.CD46 murine B cells were able to support MV replication, as shown by production of infectious virus and by cell biosynthesis of viral hemagglutinin after metabolic labeling of infected cells with [35S]methionine. These results show that the human CD46 molecule serves as an MV receptor allowing virus-cell binding, fusion, and viral replication and open new perspectives in the study of MV pathogenesis.     

Multiple viral mutations rather than host factors cause defective measles virus gene expression in a subacute sclerosing panencephalitis cell line.

A measles virus (MV) genome originally derived from brain cells of a subacute sclerosing panencephalitis patient expressed in IP-3-Ca cells an unstable MV matrix protein and was unable to produce virus particles. Transfection of this MV genome into other cell lines did not relieve these defects, showing that they are ultimately encoded by viral mutations. However, these defects were partially relieved in a weakly infectious virus which emerged from IP-3-Ca cells and which produced a matrix protein of intermediate stability. The sequences of several cDNAs related to the unstable and intermediately stable matrix proteins showed many differences in comparison with a stable matrix protein sequence and even appreciable heterogeneity among themselves. Nevertheless, partial restoration of matrix protein stability could be ascribed to a single additional amino acid change. From an examination of additional genes, we estimated that, on average, each MV genome in IP-3-Ca cells differs from the others in 30 to 40 of its 16,000 bases. The role of extreme variability of RNA virus genomes in persistent viral infections is discussed in the context of the pathogenesis of subacute sclerosing panencephalitis and of other human diseases of suspected viral etiology.     

Efficient MHC Class II-restricted presentation of measles virus to T cells relies on its targeting to its cellular receptor human CD46 and involves an endosomal pathway

The role of the measles virus (MV) receptor, human CD46, in the uptake of MV and antigen presentation by Major Histocompatibility Complex (MHC) class II molecules was investigated. Expression of CD46 in murine B cells resulted in cells highly efficient in capturing UV-inactivated MV particles and presenting both envelope hemagglutinin H and nucleoprotein N to specific T cell hybridomas. Although MV fuse with the plasma membrane of its target cells, presentation of both MV-H and -N was sensitive to inhibition by chloroquine but was not affected by a tripeptide which prevents virus-cell fusion. Whereas 50 μM of chloroquine was required to inhibit presentation of MV-H, purified H or soluble N, only a two-fold lower concentration was required to inhibit that of MV-N. This shows that some CD46-mediated captured MV particles are endocytosed, then disrupted and processed in an endosome/lysosome compartment.     

Consequences of Fas-mediated human dendritic cell apoptosis induced by measles virus

Mortality from measles virus (MV) infection is caused mostly by secondary infections associated with a pronounced immunosuppression. Dendritic cells (DCs) represent a major target of MV and could be involved in immunosuppression. In this study, human monocyte-derived DCs were used to demonstrate that DC apoptosis in MV-infected DC-T-cell cocultures is Fas mediated, whereas apoptotic T cells could not be rescued by blocking the Fas pathway. Two novel consequences of DC apoptosis after MV infection were demonstrated. (i) Fas-mediated apoptosis of DCs facilitates MV release, while CD40 activation enhances MV replication in DCs. Indeed, detailed studies of infectious MV release and intracellular MV nucleoprotein (NP) showed that inhibition of CD40-CD40L ligand interaction blocks NP synthesis. We conclude that the CD40 ligand expressed by activated T cells first enhances MV replication in DCs, and then Fas ligand produced by activated T cells induces Fas-mediated apoptosis of DCs, thus facilitating MV release. (ii) Not only MV-infected DCs but also bystander uninfected DCs undergo a maturation process confirmed by CD1a, CD40, CD80, CD86, CD83, and major histocompatibility complex type II labeling. The bystander maturation effect results from contact and/or engulfment of MV-induced apoptotic DCs by uninfected DCs. A model is proposed to explain how both a specific immune response and immunosuppression can simultaneously occur after MV infection through Fas-mediated apoptosis and CD40 activation of DCs.     

Hemadsorption expressed by cloned H genes from subacute sclerosing panencephalitis (SSPE) viruses and their possible progenitor measles viruses isolated in Osaka, Japan

Most subacute sclerosing panencephalitis (SSPE) viruses, including our Osaka-1, -2, and -3 strains isolated in Osaka, have shown negative hemadsorption (HAD) by African green monkey red blood cells. This property has been thought to be characteristic of SSPE virus as compared to the positive reaction of the standard Edmonston strain of measles virus (MV). However, this assumption has become quite obscure because MV mutates frequently at the genetic level during its multiplication and also because recent field strains isolated by lymphoblastoid cell lines have shown negative HAD. To investigate the above issue, the nucleotide sequences of the hemagglutinin (H) genes from SSPE virus Osaka-1, -2, or -3 strains were compared to those of various MV field strains isolated in Osaka by Vero cells. The H gene sequences of three SSPE strains were relatively conserved without such biased hypermutation as had been observed in the matrix (M) gene of three SSPE strains. However, this analysis of the H gene sequence of the SSPE viruses enabled us to deduce possible progenitor MVs, which are in agreement with the deduction from the M gene analysis we reported previously. The HAD of Vero cells transfected with the cloned H cDNAs from the SSPE strains and their progenitors suggested that negative HAD of the SSPE viruses has been maintained as one of original properties of the progenitor MVs rather than having been acquired as an altered one during long-term persistent infection in the brains of patients with SSPE.     

Neonatal immunization with a Sindbis virus-DNA measles vaccine induces adult-like neutralizing antibodies and cell-mediated immunity in the presence of maternal antibodies

Infants younger than age 9 mo do not respond reliably to the live attenuated measles vaccine due the immaturity of their immune system and the presence of maternal Abs that interfere with successful immunization. We evaluated the immune responses elicited by Sindbis virus replicon-based DNA vaccines encoding measles virus (MV) hemagglutinin (H, pMSIN-H) or both hemagglutinin and fusion (F, pMSINH-FdU) glycoproteins in neonatal mice born to naive and measles-immune mothers. Despite the presence of high levels of maternal Abs, neonatal immunization with pMSIN-H induced long-lasting, high-avidity MV plaque reduction neutralization (PRN) Abs, mainly IgG2a, that also inhibited syncytium formation in CD150(+) B95-8 cells. IgG secreting plasma cells were detected in spleen and bone marrow. Newborns vaccinated with pMSINH-FdU elicited PRN titers that surpassed the protective level (200 mIU/ml) but were short-lived, had low syncytium inhibition capacity, and lacked avidity maturation. This vaccine failed to induce significant PRN titers in the presence of placentally transferred Abs. Both pMSIN-H and pMSINH-FdU elicited strong Th1 type cell-mediated immunity, measured by T cell proliferation and IFN-gamma production, that was unaffected by maternal Abs. Newborns responded to measles DNA vaccines with similar or even higher PRN titers and cell-mediated immunity than adult mice. This study is the first demonstration that a Sindbis virus-based measles DNA vaccine can elicit robust MV immunity in neonates bypassing maternal Abs. Such a vaccine could be followed by the current live attenuated MV vaccine in a heterologous prime-boost to protect against measles early in life.     

浙江省麻疹病毒的基因特征分析

目的分析浙江省流行的麻疹病毒(MV)的基因特征,为更好地防控麻疹提供科学参考。方法从GenBank检索并下载浙江省所有麻疹病毒株、中国麻疹疫苗株和WHO推荐参考株的血凝素蛋白(H)和核蛋白(N)的基因组序列,利用MEGA 6.0软件进行比对分析,构建种系进化树,确定浙江省麻疹病毒流行的基因型别,并进行同源性和基因变异分析。结果浙江省麻疹病毒以H1基因型为主(27株),其他基因型为辅(2株B3型)。H1a亚型(21/27)占绝对优势,其次为H1b亚型(6/27)。浙江省所有毒株间H蛋白的氨基酸同源性为96.9%~100.0%,与疫苗株Shanghai-191和Changchun-47的同源性均为95.0%~96.0%。浙江省所有毒株间N蛋白羧基末端的氨基酸同源性为82.7%~100.0%,与疫苗株Shanghai-191的同源性为85.8%~89.5%,与疫苗株Changchun-47的同源性为87.3%~91.0%。结论麻疹病毒H1基因型为浙江省麻疹流行的优势株,与现行参考疫苗株(A基因型)差异较大,因此针对麻疹病毒H1基因型疫苗的研制是今后浙江省麻疹病毒防控的关键。     

Differential type I IFN-inducing abilities of wild-type versus vaccine strains of measles virus

Laboratory adapted and vaccine strains of measles virus (MV) induced type I IFN in infected cells. The wild-type strains in contrast induced it to a far lesser extent. We have investigated the mechanism for this differential type I IFN induction in monocyte-derived dendritic cells infected with representative MV strains. Laboratory adapted strains Nagahata and Edmonston infected monocyte-derived dendritic cells and activated IRF-3 followed by IFN-beta production, while wild-type MS failed to activate IRF-3. The viral IRF-3 activation is induced within 2 h, an early response occurring before protein synthesis. Receptor usage of CD46 or CD150 and nucleocapsid (N) protein variations barely affected the strain-to-strain difference in IFN-inducing abilities. Strikingly, most of the IFN-inducing strains possessed defective interference (DI) RNAs of varying sizes. In addition, an artificially produced DI RNA consisting of stem (the leader and trailer of MV) and loop (the GFP sequence) exhibited potential IFN-inducing ability. In this case, however, cytoplasmic introduction was needed for DI RNA to induce type I IFN in target cells. By gene-silencing analysis, DI RNA activated the RIG-I/MDA5-mitochondria antiviral signaling pathway, but not the TLR3-TICAM-1 pathway. DI RNA-containing strains induced IFN-beta mRNA within 2 h while the same recombinant strains with no DI RNA required >12 h postinfection to attain similar levels of IFN-beta mRNA. Thus, the stem-loop structure, rather than full genome replication or specific internal sequences of the MV genome, is required for an early phase of type I IFN induction by MV in host cells.     

V domain of human SLAM (CDw150) is essential for its function as a measles virus receptor

Human signaling lymphocytic activation molecule (SLAM; also known as CDw150) has been shown to be a cellular receptor for measles virus (MV). Chinese hamster ovary cells transfected with a mouse SLAM cDNA were not susceptible to MV and the vesicular stomatitis virus pseudotype bearing MV envelope proteins alone, indicating that mouse SLAM cannot act as an MV receptor. To determine the functional domain of the receptor, we tested the abilities of several chimeric SLAM proteins to function as MV receptors. The ectodomain of SLAM comprises the two immunoglobulin superfamily domains (V and C2). Various chimeric transmembrane proteins possessing the V domain of human SLAM were able to act as MV receptors, whereas a chimera consisting of human SLAM containing the mouse V domain instead of the human V domain no longer acted as a receptor. To examine the interaction between SLAM and MV envelope proteins, recombinant soluble forms of SLAM were produced. The soluble molecules possessing the V domain of human SLAM were shown to bind to cells expressing the MV hemagglutinin (H) protein but not to cells expressing the MV fusion protein or irrelevant envelope proteins. These results indicate that the V domain of human SLAM is necessary and sufficient to interact with the MV H protein and allow MV entry.     

梅州市两次麻疹疫苗强化免疫效果分析

目的综合评估分析梅州市两次麻疹疫苗强化免疫效果,为消除麻疹提供科学依据。方法综合分析麻疹疫苗强化免疫现场调查资料、评估法定传染病报告系统中麻疹发病率的变化;随机对辖区内1～12岁健康儿童216名,采用酶联免疫吸附试验(ELISA)进行强化免疫前及完成二次强化免疫后麻疹lgG抗体水平监测。结果监测人群完成二次强化免疫后麻疹IgG抗体阳性率达100.00%(216/216),2009年强化组、2010年强化组麻疹IgG抗体保护率和几何平均滴度(GMT)分别为82.08%、87.62%和1958.83、2050.26,均显著高于强化免疫前;2009年强化免疫后麻疹年发病率由强化免疫前五年平均发病率1.71/10万下降至0.22/10万,下降率87.13%,2010年强化后麻疹年发病率再次下降(0.039/10万),下降率82.27%。结论梅州市两次麻疹疫苗强化免疫效果显著,均大幅度降低了麻疹发病率、提高了人群麻疹抗体水平。