Purification of measles virus H polypeptide and of F polypeptide

Large-scale preparation of biologically active measles virus haemagglutinin expressed by attenuated vaccinia virus vectors

A procedure described here allows the efficient and rapid purification of histidine-tagged measles virus haemagglutinin that is synthesized under the control of powerful promoters (PSFJ1-10 and PSFJ2-16) of the highly attenuated vaccinia virus (VV) strain LC16mO. A single affinity chromatography step purifies recombinant haemagglutinin proteins from the lysates of cells infected with the recombinant VVs. The recovery and purity are both very high (a yield of 0.5-2.8 mg/10(8) cells and purity of >94-98%), indicating that this procedure is approximately 400 times more efficient than the conventional methods used to prepare haemagglutinin. The haemagglutinins are correctly transported to the cell surface and have haemadsorption activity. Moreover, the recombinant haemagglutinin proteins cooperate with the measles virus fusion protein to elicit cell fusion activity. In addition, the antibody titres against measles virus, as measured by enzyme-linked immunosorbent assay using the purified haemagglutinin as the capture antigen, correlated closely with neutralization test titres (R(2) = 0.84, p < 0.05), indicating the preservation of immunologically relevant antigenicity. Such recombinant haemagglutinin preparations will be useful in diagnostic tests that measure functional anti-measles immunity and investigate the biological functions and structure of the haemagglutinin.

Functional and structural interactions between measles virus hemagglutinin and CD46

We analyzed the roles of the individual measles virus (MV) surface glycoproteins in mediating functional and structural interactions with human CD46, the primary MV receptor. On one cell population, recombinant vaccinia virus vectors were used to produce the MV hemagglutinin (H) and fusion (F) glycoproteins. As fusion partner cells, various cell types were examined, without or with human CD46 (endogenous or recombinant vaccinia virus encoded). Fusion between the two cell populations was monitored by a quantitative reporter gene activation assay and by syncytium formation. MV glycoproteins promoted fusion with primate cells but not with nonprimate cells; recombinant CD46 rendered nonprimate cells competent for MV glycoprotein-mediated fusion. Markedly different fusion specificity was observed for another morbillivirus, canine distemper virus (CDV): recombinant CDV glycoproteins promoted fusion with primate and nonprimate cells independently of CD46. Fusion by the recombinant MV and CDV glycoproteins required coexpression of H plus F in either homologous or heterologous combinations. To assess the role of H versus F in determining the CD46 dependence of MV fusion, we examined the fusion specificities of cells producing heterologous glycoprotein combinations. The specificity of HMV plus FCDV paralleled that observed for the homologous MV glycoproteins: fusion occurred with primate cells but not with nonprimate cells unless they produced recombinant CD46. By contrast, the specificity of HCDV plus FMV paralleled that for the homologous CDV glycoproteins: fusion occurred with either primate or nonprimate cells with no dependence on CD46. Thus, for both MV and CDV, fusion specificity was determined by H. In particular, the results demonstrate a functional interaction between HMV and CD46. Flow cytometry and antibody coprecipitation studies provided a structural correlate to this functional interaction: CD46 formed a molecular complex with HMV but not with FMV or with either CDV glycoprotein. These results highlight the critical role of the H glycoprotein in determining MV specificity for CD46-positive cells.

Isolation of the measles virus hemagglutinin protein in a soluble form by protease digestion

The hemagglutinin (H) glycoprotein was isolated in a soluble form by digesting measles virus particles with an endoproteinase, Asp-N (from a Pseudomonas fragi mutant). Digestion of H with Asp-N brought about glycopeptides in three different forms, depending on the cleaving site: AHD, which has an M(r) of 66,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and which formed a disulfide-linked homodimer with an M(r) of 132,000, and two monomeric digestion products, AHM-1 (with an M(r) of 64,000) and AHM-2 (with an M(r) of 58,000). The susceptibility of the H glycoprotein to the protease depended on the enzyme concentration. AHD was readily formed at a low concentration of Asp-N, while AHM-1 and AHM-2 required higher and even higher protease concentrations, respectively. All of the cleavage products reacted with monoclonal antibodies to various epitopes of the H protein; however, only AHD showed a significant hemagglutinin activity on African green monkey erythrocytes. The hemagglutinin activities of AHM-1 and AHM-2 were restored after a monoclonal antibody lacking the hemagglutination-inhibiting activity was added to the reaction mixture. AHDs purified by size-exclusion high-pressure liquid chromatography had two associating forms; one had an M(r) higher than and the other an M(r) as high as that of a tetramer. The former was associated noncovalently in addition to having two intermolecular disulfide bonds, and the latter was associated covalently with a single intermolecular disulfide bond and was also duplicated through a noncovalent association. In addition, both AHM-1 and AHM-2, having no intermolecular disulfide bond, were in a dimer form. These results suggest that AHM-1 and AHM-2 are monovalent in the hemagglutinin activity, while AHDs are divalent. Comparative analyses of the N termini of these soluble glycopeptides with the sequence of H suggested that the cysteine residue at position 139 was responsible for the intermolecular disulfide bonding between the monomeric H glycoproteins. The cysteine at position 154 was also suggested to participate in the forming of the intermolecular disulfide bond.

Humoral immune response elicited in rats by measles viral membrane antigens presented in liposomes and ISCOMs

The immunogenicity of measles virus glycoproteins presented associated to liposomes or ISCOMs was compared with that of whole virus and solubilized membrane proteins in W/Fu rats. The rats were immunized three times at ten-day intervals with syngeneic peritoneal exudate cells fed in vitro with the various antigen preparations. A strong and persisting antibody response with haemagglutinin inhibitory and neutralization activity was observed in rats immunized with liposomes, ISCOMs, or virus. The responses were very similar despite the lower dose of protein received by rats immunized with ISCOMs (1 microgram protein) or with liposomes (20 micrograms protein). By contrast, injection of peritoneal exudate cells previously fed in vitro with soluble H and F glycoproteins resulted in only a poor and transient response. The sera from rats immunized with virus, liposomes or ISCOMs contained antibodies immunoprecipitating mainly H and F glycoproteins. Despite a strong enrichment in F polypeptides during the preparation of ISCOMs, they induced an equal anti-H and anti-F antibody response.

IgM antibodies in sera from patients with chronic active hepatitis reacting with the measles virus matrix protein and nucleoprotein

The antigenic specificity of measles virus IgM antibodies in sera from patients with chronic active hepatitis not caused by hepatitis B virus has been examined. An immunosorbent column containing antihuman IgM covalently bound to Sepharose was used to pick up IgM from the sera. Radiolabelled measles virus antigens were then allowed to react with the IgM antibodies. The immune complexes were eluted and analysed by sodium dodecyl sulfate [SDS]-polyacrylamide gel electrophoresis. Four sera from patients with hepatitis B surface antigen [HBsAg]-negative chronic active hepatitis with high measles virus haemagglutination inhibition [HI] and complement fixation [CF] antibody titres and positive enzyme-linked immunosorbent assay [ELISA] for measles-virus-specific IgM were examined. The results were compared with those obtained using sera from patients with an acute measles virus infection and from healthy controls. In both patient groups, IgM antibodies with specificity against the matrix protein represented the major portion of the measles virus IgM. IgM antibodies against the measles virus nucleoprotein and probably against host-cell-derived actin were also present. The patient sera contained only traces of IgM antibodies with specificity against the measles virus haemagglutinin or fusion protein. No specific IgM antibodies were found in sera from healthy controls.