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Measles virus: both the haemagglutinin and fusion glycoproteins are required for fusion

Vaccinia-measles recombinant viruses were used to examine the contribution of the individual measles virus glycoproteins in fusion. Although vaccinia virus recombinants expressing either the haemagglutinin or fusion proteins did not induce fusion in the cell lines examined, a double recombinant expressing both measles virus glycoproteins gave extensive syncytia in cells of human and simian origin. No fusion was observed in mouse, hamster or chicken cells. The fusion induced by the double recombinant could be specifically inhibited with either anti-fusion or anti-haemagglutinin monoclonal antibodies.

Measles virus haemagglutinin induces down-regulation of gp57/67, a molecule involved in virus binding.

A surface glycoprotein (gp57/67) was previously shown to be involved in measles virus (MV) binding and characterized in our laboratory. Here, we described down-regulation of cell surface gp57/67 after infection with MV. This effect is specific for MV since cells infected with canine distemper virus, closely related to MV, did not down-regulate gp57/67. The decrease in cell surface gp57/67 correlated with expression of MV glycoproteins and more particularly with the expression of MV haemagglutinin (MV-H). Indeed, expression of MV-H after infection with a vaccinia virus recombinant coding for MV-H was necessary and sufficient to induce down-regulation of gp57/67. Kinetics of cell surface expression of MV-H and gp57/67 showed that the degree of down-regulation was correlated with the amount of MV-H expressed by infected cells. Experiments using antibody-prelabelled gp57/67 and indirect immunofluorescence microscopy allowed us to follow the fate of gp57/67 and showed that down-regulation was occurring by rapid internalization of gp57/67 from the cell surface. These results provide additional evidence that the gp57/67 molecule is closely associated with the pathway of MV infection and also reveal a phenomenon which may be related to viral pathogenesis and persistence.

Class I-restricted CTL induction by mucosal immunization with naked DNA encoding measles virus haemagglutinin.

We have investigated the class I-restricted CTL response specific for measles virus haemagglutinin (HA) in the spleens of mice immunized by various mucosal routes with a DNA plasmid carrying the HA gene (pV1j-HA). A single immunization with recombinant DNA injected in the buccal mucosa induced an HA-specific CTL response. Similarly, nasal immunization with the DNA vaccine induced primary CTLs against measles virus HA. Booster immunization did not enhance the CTL activity. Oral or intrajejunal immunization with the plasmid induced a CTL response of lower magnitude. However, this could be potentiated by co-administration of the mucosal adjuvant cholera toxin or cationic lipids (DOTAP). These data show that a CTL response can be generated by mucosal vaccination using DNA vaccines.

A monoclonal antibody recognizes a human cell surface glycoprotein involved in measles virus binding.

Measles virus (MV) has a very limited host range, humans being the only natural reservoir of the virus. This restriction may be due to the absence of an MV receptor on the surface of non-primate cells. We have studied the MV-binding ability of several cell lines and attempted to characterize the receptor by studying the binding of 35S-labelled MV and by a rosette formation technique. We confirmed that all the human cell lines examined (HeLa, Raji and Jurkat) bound MV and that the murine cell lines (BW and L) did not. The glycoprotein nature of the receptor activity was demonstrated by the fact that it could be removed from the cell membrane using proteolytic enzymes and by its failure to be re-expressed in the presence of a protein synthesis inhibitor or an N-glycosylation inhibitor. A monoclonal antibody isolated after immunization of mice with Raji cells specifically inhibited MV binding and infection of human cells, and recognized human and simian but not murine cells. Depending on the cell line (HeLa, Raji, Jurkat or Vero), this antibody immunoprecipitated one or two glycoproteins with apparent M(r)s of 57K and/or 67K from human and simian cells, but not from murine cells.

Measles virus antigens induce both type-specific and canine distemper virus cross-reactive cytotoxic T lymphocytes in mice: localization of a common Ld-restricted nucleoprotein epitope.

We have studied the induction of the cytotoxic T lymphocyte (CTL) response to measles virus (MV) antigens expressed as vaccinia virus (VV) recombinants in a murine model. In C3H mice (H-2k) only the nucleoprotein (NP) induced a CTL response and this was shown to be cross-reactive with the closely related canine distemper virus (CDV). The presentation of this antigen was shown to be Kk-restricted. In BALB/c mice (H-2d), both the haemagglutinin (HA) and the NP induced a strong CTL response, the former being serotype-specific, whereas the latter cross-reacted with CDV. Both responses were found to be Ld-restricted. Based on the prediction for Ld T cell motifs, we tested a number of MV NP-derived nonapeptides for their capacity to sensitize P815 cells (H-2d) for lysis by spleen cells from VV-NP-immunized mice. One of these peptides, comprising amino acids 281 to 289 (Tyr-Pro-Ala-Leu-Gly-Leu-His-Glu-Phe) was as effective as cells expressing the complete NP protein. This motif is conserved in the CDV NP.

Mode of entry of morbilliviruses

The morbilliviruses have a restricted host range. This is probably dependent on the use of specific host cell receptors. In the present article, we have reviewed our approach to identify a host cell receptor for one of the morbilliviruses, measles virus and to elucidate the interaction between viral and cellular proteins during virus entry into the host cell.

The ectodomain of measles virus envelope glycoprotein does not gain access to the cytosol and MHC class I presentation pathway following virus-cell fusion.

To unravel the intracellular fate of measles virus (MV) haemagglutinin (H) following fusion of the virus envelope with the cell membrane, its presentation by MHC molecules to T cells was explored. After MV infection, murine cells expressing CD46 were lysed by MHC class I-restricted CD8 CTLs specific for the ectodomain of H. In contrast, when sensitized with UV-inactivated MV, they were not lysed by these effectors, but were recognized by H-specific and class II-restricted CD4 CTLs. Thus, after MV binding and fusion, H becomes associated with plasma membrane and its ectodomain can reach the endosomal MHC-II but not the cytosolic MHC-I antigen presentation pathway. From these data and a reappraisal of previous reports, it appears that the ectodomains of both MV haemagglutinin fusion proteins, having undergone the fusion step, are not translocated into the cytosol and end up in the endosomes.