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The disulfide-linked glycoprotein B (gB; gp55-116) complex of human cytomegalovirus represents the most abundant and immunogenic component of the virion envelope. We have studied the oligomerization and transport of this molecule, using a series of murine monoclonal antibodies. Our results indicated that oligomerization of this molecule occurred shortly after its synthesis, with a half-time of maximal formation of approximately 25 min. The oligomeric form had an estimated mass of 340,000 Da and likely consisted of a homodimer of the gp55-116 complex. By using a conformation-specific monoclonal antibody, postoligomerization folding of this molecule was demonstrated. This event exhibited an unusually prolonged half-maximal time of approximately 160 min. Both oligomerization and folding occurred in the endoplasmic reticulum. Oligomerization and folding occurred in the absence of carbohydrate modifications, although likely at lower efficiency. Finally, the oligomeric and folded forms were shown to be transported to the surface of infected cells and infectious virions.

The gene encoding the major envelope glycoprotein complex, gp55-116 (gB), of human cytomegalovirus (HCMV) was expressed at high levels in insect cells utilizing a recombinant baculovirus. The mature intracellular form of the insect-derived gp55-116 was a protein of Mr 150K which contained approximately 50K of N-linked oligosaccharides. The oligosaccharide linkages were almost exclusively endoglycosidase H-sensitive. The 150K protein was processed, presumably by proteolytic cleavage, to yield at least one of the previously defined cleavage products of the gp55-116. This processing step was significantly less efficient in insect cells than the analogous step in mammalian cells. Finally, the insect-derived gp55-116 was highly immunogenic in experimental animals and readily recognized by antibodies contained within HCMV-immune human serum, suggesting that this recombinant protein warrants further study as a potential HCMV subunit vaccine candidate.

Cell surface expression of the human cytomegalovirus (HCMV) major envelope glycoprotein complex, gp55-116 (gB), was studied by using monoclonal antibodies and an HCMV gp55-116 (gB) recombinant vaccinia virus. HCMV-infected human fibroblasts and recombinant vaccinia virus-infected HeLa cells expresses three electrophoretically distinct proteins of Mr 170,000, 116,000, and 55,000 on their surface. These species have been previously identified within infected cells and purified virions. Two unique neutralizing epitopes were shown to be present on the cell surface gp55-116 (gB). Utilizing HeLa cells infected with the gp55-116 recombinant vaccinia virus as a specific immunosorbent, we have shown that approximately 40 to 70% of the total serum virus-neutralizing activity of a group of individuals with past HCMV infections was directed against this single envelope glycoprotein. The implications of this finding for vaccine development are discussed.

Human cytomegalovirus (HCMV)-specific antibodies were assayed in cord serum and the respective maternal serum from two groups of newborn infants with congenital HCMV infection. One group of infants exhibited clinically apparent infection with multiple organ system involvement, whereas the second group had subclinical infections. Levels of virus-specific IgG antibodies reactive with several virus-encoded proteins including those reactive with the major envelope glycoprotein complex were significantly higher in cord serum and maternal delivery serum from the group of infants with clinically apparent infection than in serum from those with subclinical infection. Maternal delivery serum from the group with subclinical infection had significantly higher levels of IgM virus-binding antibody and lower levels of IgG virus-binding antibody than did the respective serum from the group with clinically apparent infection, suggesting maternal acquisition occurred later in gestation in the group with subclinical infection. These results suggested that deficiencies in the HCMV-specific antibody response were not associated with clinically apparent congenital infection and that other factors, such as early virus acquisition during pregnancy, might contribute to the severity of intrauterine HCMV infection.

The human cytomegalovirus (HCMV) envelope glycoprotein complex gp55-116 was expressed in both Escherichia coli and cells infected with a recombinant vaccinia virus. E. coli produced a single protein of Mr 100,000 which approximated the size of the nonglycosylated gp55-116 precursor found in HCMV-infected cells. Cells infected with the recombinant vaccinia virus contained three intracellular forms of Mr 160,000, 150,000, and 55,000 which were detected by a monoclonal antibody reactive with gp55. Comparison of the immunological properties of these recombinant proteins indicated that several of the HCMV gp55-116 monoclonal antibodies and sera from patients infected with HCMV reacted with the vaccinia virus-derived proteins whereas a more restricted group of monoclonal antibodies recognized the E. coli-produced protein. Immunization of mice with either E. coli or vaccinia virus recombinant HCMV gp55-116 resulted in production of virus-neutralizing antibodies. In contrast to the almost exclusive production of complement-dependent neutralizing antibodies following immunization with recombinant vaccinia virus, the E. coli-derived protein induced complement-independent neutralizing antibodies.

Murine monoclonal antibodies and polyvalent monospecific antisera reactive with an abundant 68,000 Mr (p68) human cytomegalovirus (CMV) virion protein were used to characterize this protein within CMV-infected cells. The protein was found to partition within the nucleus and cytoplasm of infected cells. Pulse-chase analysis indicated the p68 was degraded into three proteins of 52,000, 51,000 and 50,000 Mr which were found only within infected cells. Both cellular forms as well as the virion p68 were phosphorylated but non-glycosylated. The p68 was synthesized shortly after infection and in the presence of cytosine arabinoside, an inhibitor of viral DNA replication. Studies with monospecific antisera and a panel of monoclonal antibodies specific for the p68 suggested that this protein was not expressed on the surface of infectious virions or infected cells.

We have developed a murine monoclonal antibody reactive with a major immediate early 72,000 dalton protein of human cytomegalovirus and utilized this reagent in a rapid virus titration and microneutralization assay. Because of the early expression of this virus encoded protein, both assays could be accomplished within 16 h following virus inoculation. In addition, both assays resulted in considerable savings of reagents because the assays were carried out in 96-well microtiter plates. These assays should prove useful in the preparation and study of neutralizing antibodies directed against human cytomegalovirus.

Human cytomegalovirus contains an envelope glycoprotein of 58 kilodaltons (gp58). The protein, which is derived from a glycosylated precursor molecule of 160 kilodaltons via proteolytic cleavage, is capable of inducing neutralizing antibodies. We have mapped the epitopes recognized by the neutralizing monoclonal antibody 7-17 and a second antibody (27-287) which is not neutralizing. Overlapping fragments of the carboxy-terminal part of the open reading frame coding for gp58 were expressed in Escherichia coli as beta-galactosidase fusion proteins. The reactivities of antibodies 7-17 and 27-287 were determined by Western blot (immunoblot) analysis. Both antibodies recognized sequences between amino acids 608 and 625 of the primary gp58 translation product. The antibodies almost completely inhibited one another in a competitive binding assay with intact virus as antigen. Moreover, antibody 27-287 was able to inhibit the complement-independent neutralizing activity of antibody 7-17.

The processing pathway of the major envelope glycoprotein complex, gp55-116 (gB), of human cytomegalovirus was studied using inhibitors of glycosylation and endoglycosidases. The results of these studies indicated that the mature gp55-116 is synthesized by the addition of both simple and complex N-linked sugars to a nonglycosylated precursor of estimated Mr 105,000. In a rapid processing step, the Mr 105,000 precursor is glycosylated to a protein of Mr 150,000 (gp150) which contains only endoglycosidase H-sensitive sugar linkages. The gp150 is then processed relatively slowly to a Mr 165,000 to 170,000 species (gp165-170), which is then cleaved to yield the mature gp55-116. Monensin prevented the final processing steps of the gp150, including cleavage, suggesting that transport through the Golgi apparatus is required for complete processing. Digestion of the intracellular forms of this complex as well as the virion forms confirmed the above findings and indicated that the mature virion form of gp55 contains 8,000 daltons of N-linked sugars. The virion gp116 contains some 52,000 to 57,000 daltons of N-linked carbohydrates and approximately 5,000 daltons of O-linked sugars.

A typing scheme was used to test 15 strains of Streptococcus uberis according to their production of (P-type) and sensitivity to (S-type) bacteriocin-like inhibitory substances. Twelve of the strains were inhibitor producers and nine different P-types were detected. All of the strains were typable according to inhibitor sensitivity, ten different S-types being distinguished. Both the P-type and S-type designations of the strains were reproducible on repeated testing. By combination of P-typing and S-typing, highly discriminatory inhibitor 'fingerprints' of the strains could be obtained. This scheme would appear to have considerable potential for typing isolates of Str. uberis as an aid to investigations into the epidemiology of Str. uberis mastitis in dairy cattle.