Wild-type measles virus induces large syncytium formation in primary human small airway epithelial cells by a SLAM(CD150)-independent mechanism

Measles virus: cellular receptors, tropism and pathogenesis

Measles virus(MV), a member of the genusMorbillivirusin the familyParamyxoviridae, is an enveloped virus with a non-segmented, negative-strand RNA genome. It has two envelope glycoproteins, the haemagglutinin (H) and fusion proteins, which are responsible for attachment and membrane fusion, respectively. Human signalling lymphocyte activation molecule (SLAM; also called CD150), a membrane glycoprotein of the immunoglobulin superfamily, acts as a cellular receptor for MV. SLAM is expressed on immature thymocytes, activated lymphocytes, macrophages and dendritic cells and regulates production of interleukin (IL)-4 and IL-13 by CD4+T cells, as well as production of IL-12, tumour necrosis factor alpha and nitric oxide by macrophages. The distribution of SLAM is in accord with the lymphotropism and immunosuppressive nature of MV.Canine distemper virusandRinderpest virus, other members of the genusMorbillivirus, also use canine and bovine SLAM as receptors, respectively. Laboratory-adapted MV strains may use the ubiquitously expressed CD46, a complement-regulatory molecule, as an alternative receptor through amino acid substitutions in the H protein. Furthermore, MV can infect SLAM−cells, albeit inefficiently, via the SLAM- and CD46-independent pathway, which may account for MV infection of epithelial, endothelial and neuronal cellsin vivo. MV infection, however, is not determined entirely by the H protein–receptor interaction, and other MV proteins can also contribute to its efficient growth by facilitating virus replication at post-entry steps. Identification of SLAM as the principal receptor for MV has provided us with an important clue for better understanding of MV tropism and pathogenesis.

Interactions among measles virus hemagglutinin, fusion protein and cell receptor signaling lymphocyte activation molecule (SLAM) indicating a new fusion-trimer model

For measles viruses, fusion on the cell membrane is an important initial step in the entry into the infected cells. The recent research indicated that hemagglutinin firstly leads the conformational changes in the fusion protein then co-mediates the membrane fusion. In the work, we use the co-immunoprecipitation and pull-down techniques to identify the interactions among fusion protein, hemagglutinin and signaling lymphocyte activation molecule (SLAM), which reveal that the three proteins can form a functional complex to mediate the SLAM-dependent fusion. Moreover, under the confocal microscope, fusion protein and hemagglutinin protein can show the cocapping mediated by the SLAM. So fusion protein not only is involved in the fusion but also might directly interact with the SLAM to be a new fusion-trimer model, which might account for the infection mechanism of measles virus.

Wild-type Rinderpest virus uses SLAM (CD150) as its receptor

Rinderpest virus (RPV) is a morbillivirus, related closely to the human pathogen Measles virus (MV). Although cell culture-adapted strains of RPV can infect many kinds of cell from different hosts, one such strain has previously been shown to have a detectable preference for cells expressing the MV receptor CD150 (SLAM), a protein found only on certain types of activated T cells, B cells and dendritic cells. Here, it is shown that the wild-type, virulent parent of the most common vaccine strain of RPV requires CD150 as a receptor, whilst the cell culture-adapted vaccine strain has acquired the ability to use heparan sulphate as an alternative receptor.

DC-virus interplay: a double edged sword

Myeloid and plasmacytoid dendritic cells, a family of professional antigen presenting cells, are crucial in generating and maintaining anti-viral immunity. Many viruses have evolved to avoid, subvert, and even counterattack them. In this article, we focus on the tuning of innate and adaptive responses induced by human dendritic cells, and on the inhibition of their functions by viruses of medical significance. A constant "tug of war" goes on between dendritic cells and viruses and a main dendritic cell countermeasure is cross-presentation/priming.

Cell tropism of wild-type measles virus is affected by amino acid substitutions in the P, V and M proteins, or by a truncation in the C protein

Two nucleotide differences in the P/C/V and M genes between B95a cell- and Vero cell-isolated wild-type measles viruses (MV) have previously been found from the same patient. The nucleotide difference in the P/C/V gene resulted in an amino acid difference (M175I) in the P and V proteins and a 19 aa deletion in the C protein. The nucleotide difference in the M gene resulted in an amino acid difference (P64H) in the M protein. To verify this result and to examine further whether the amino acid difference or truncation is important for MV cell tropism, recombinant MV strains containing one of the two nucleotide substitutions, or both, were generated. It was found that the P64H substitution in the M protein was important for efficient virus growth and dissemination in Vero cells and that the M175I substitution in the P and V protein or truncation of the C protein was required for optimal growth.

Measles virus (MV) hemagglutinin: evidence that attachment sites for MV receptors SLAM and CD46 overlap on the globular head

Measles virus hemagglutinin (MVH) residues potentially responsible for attachment to the wild-type (wt) MV receptor SLAM (CD150) have been identified and localized on the MVH globular head by reference to a revised hypothetical structural model for MVH (www.pepscan.nl/downloads/measlesH.pdb). We show that the mutation of five charged MVH residues which are conserved among morbillivirus H proteins has major effects on both SLAM downregulation and SLAM-dependent fusion. In the three-dimensional surface representation of the structural model, three of these residues (D505, D507, and R533) align the rim on one side of the cavity on the top surface of the MVH globular head and form the basis of a single continuous site that overlaps with the 546-548-549 CD46 binding site. We show that the overlapping sites fall within the footprint of an anti-MVH monoclonal antibody that neutralizes both wt and laboratory-vaccine MV strains and whose epitope contains R533. Our study does not exclude the possibility that Y481 binds CD46 directly but suggests that the N481Y mutation of wt MVH could influence, at a distance, the conformation of the overlapping sites so that affinity to CD46 increases. The relevance of these results to present concepts of MV receptor usage is discussed, and an explanation is proposed as to why morbillivirus attachment proteins are H, whereas those from the other paramyxoviruses are HN (hemagglutinin-neuraminidase).