Richard C. Gehrz

SPECIFIC CELL-MEDIATED IMMUNE DEFECT IN ACTIVE CYTOMEGALOVIRUS INFECTION OF YOUNG CHILDREN AND THEIR MOTHERS

4 young children with active cytomegalovirus (C.M.V.) infection were found, by an in-vitro lymphocyte-proliferation assay, to have a C.M.V.-specific cell-mediated immune defect. These children had antibodies to C.M.V. and were actively shedding C.M.V. in the urine when studied. Their general cellular immune responses were intact, with normal numbers of T lymphocytes and normal in-vitro responses to mitogens and at least one antigen. 3 of the 4 mothers studied shortly after delivery had decreased cell-mediated immunity to C.M.V. These findings suggest that an antigen-specific immune defect facilitates transmission of virus from mother to infant and permits persistence of viral replication in the offspring.

Human cytomegalovirus structural proteins.

Introduction. Members of the Herpesviridae family are viruses with a core containing the viral DNA in the form of a torus, a capsid (100 nm in diameter and composed of 162 capsomers), a tegument, which is a structure of variable thickness between the capsid and the envelope, and an envelope. The envelope is the trilaminar outer covering which contains numerous protrusions of spikes consisting of virally encoded glycoproteins. The resulting diameter of the virion varies from 120 to 300 nm. Herpesviruses have been divided into three subfamilies on the basis of biological properties. The Alphaherpesvirinae are herpesviruses with a variable host range, short replication cycle, rapid spread in cultured cells, a lytic effect on infected cells and a tropism for establishing a latent infection in sensory ganglia. The Betaherpesvirinae have a restricted host range, a longer replication cycle, an infection which progresses more slowly in cultured cells and a latent state that can be established in numerous cells and tissues.

A longitudinal analysis of lymphocyte proliferative responses to mitogens and antigens during human pregnancy

T-cell number and mitogen- and antigen-induced lymphocyte proliferative were assessed longitudinally in 18 normal human pregnancies to examine the effects of pregnancy on cellular immunity. The T-cell percentage and mitogen-induced responses did not change significantly in pregnant women as compared to nonpregnant, non-postpartum control adults. However, cell-mediated immune responses to three antigens were dramatically depressed during the third trimester and then returned to early pregnancy levels by 90 days post partum. This reduction in antigen-specific cellular immunity may be necessary to prevent rejection of the histoincompatible fetus by the mother and at the same time may render women in late gestation more susceptible to infection.

Characterization of a human cytomegalovirus glycoprotein complex (gcI).

Three distinct families of glycoprotein complexes present in the envelopes of human cytomegalovirus and designated gcI, gcII and gcIII have been described recently. The synthesis of the gcI family was analysed using either inhibitors of glycoprotein processing and transport or endoglycosidase treatments of purified glycoproteins. The initial step in gcI synthesis involved the glycosylation of a 95K protein (p95) to form a high-mannose, simple N-linked glycoprotein of Mr 158K (gp158), which was detected only in the presence of the glycoprotein processing inhibitor castanospermine. This intermediate was rapidly trimmed in the virus-infected cell to form a more stable simple N-linked precursor glycoprotein of Mr 138K (gp138). Treatment of either gp158 or gp138 with endoglycosidase H produced p95. Both molecules, gp158 and gp138, were found in disulphide-linked complexes which are presumably infected cell precursors to gcI since they were not found in virions. The processing of these complexes involved complete cleavage of gp138 and conversion of some but not all of its oligosaccharide to complex N-linked chains. Both processing events were inhibited by the ionophore monensin. Mature gcI contained the gp138 cleavage product, gp93-130. The latter glycoprotein could be separated into two electrophoretic forms, gp93 and gp130. The deglycosylated form of gp55 had a discrete banding pattern with an apparent Mr of 46K (p46). In contrast, the deglycosylated forms of gp93 and gp130 had diffuse banding patterns with apparent Mr values of 46K to 56K (p46-56) and 60K to 70K (p60-70) respectively. Peptide profiles comparing gp93 with gp130 indicated that they have highly similar polypeptide backbones. Since the deglycosylated forms of gp55 and gp130, 46K and 60K to 70K, respectively, together exceed the 95K precursor/deglycosylated intermediate in Mr, we propose that the above glycoproteins are derived by an alternative proteolytic cleavage of the precursor. The heterogeneous electrophoretic properties of the deglycosylated forms of gp93 and gp130 may be due to additional post-translational modifications other than glycosylation.

STRUCTURE AND COMPOSITION OF A FAMILY OF HUMAN CYTOMEGALOVIRUS GLYCOPROTEIN COMPLEXES DESIGNATED GC-I (GB)

Murine monoclonal antibodies (MAbs) were made to the 52,000 (gp52) and the 93,000 to 130,000 Mr (gp93-130) glycoproteins from a human cytomegalovirus (HCMV) glycoprotein complex designated gC-I or the gB homologue. MAbs recognizing either gp52 or gp93-130 could immunoprecipitate unreduced gC-I complexes from non-ionic detergent extracts of HCMV. Western blotting was performed with immunoaffinity-purified gC-I complexes which were reduced prior to analysis. MAbs made against gp52 recognized gp52 and a 158,000 Mr glycoprotein (gp158). MAbs which recognized gp93-130 in a Western blot also reacted with gp158, which is a gC-I precursor glycoprotein. The origin of gp93-130 was demonstrated by the reactivity of our gp93-130 MAbs with a recombinant protein containing the N-terminal portion of the gB gene. These data are consistent with the hypothesis that gp52 and gp93-130 are generated from the same high Mr precursor by proteolysis. MAbs recognizing either gp52 or gp93-130 neutralized Towne strain HCMV, but MAbs recognizing gp52 required complement to neutralize whereas MAbs recognizing gp93-130 did not. It was also determined that gp93-130 and gp 158 have detectable amounts of O-linked glycans but gp52 does not, showing a difference in the glycosylation of these glycoproteins. Analysis of gC-I disulphide bonds showed that two types were present, one which was very susceptible to reduction and a second which was less susceptible. These complexes could consist of very susceptible inter-complex disulphide bonds and less susceptible intra-complex disulphide bonds.

Molecular analysis of the immune response to human cytomegalovirus glycoprotein B (gB). II. Low gB-specific T and B cell responses are associated with expression of certain HLA-DR alleles.

Human cytomegalovirus (HCMV) is a common cause of congenital infection leading to birth defects and a leading cause of serious illness in patients with immunodeficiencies. Studies in this laboratory have focused on a molecular analysis of the immune response to glycoprotein B (gB) of HCMV. This protein has been shown to elicit B cell, helper T cell (Th), and cytotoxic T cell responses, suggesting that it may be useful as a subunit HCMV vaccine. However, previous studies showed that although peripheral blood mononuclear cells (PBMC) from all HCMV-seropositive donors proliferate in response to stimulation with whole HCMV, not all donors respond to purified recombinant gB. In the present study, PBMC from HCMV-seropositive donors homozygous for HLA-DR were tested for proliferative responses to whole HCMV and to purified gB expressed in vaccinia virus. PBMC from all donors proliferated in response to HCMV, but those from multiple donors expressing the HLA-DR3Dw3 and -DR4Dw4 specificities, and single donors expressing the -DR15Dw2, -DR13Dw19 and -DR14Dw9 specificities, failed to respond to gB. These results suggested a possible HLA-DR association with low proliferative responses to gB. In further studies, PBMC from donors expressing both putative gB-high responder and low responder HLA-DR alleles were stimulated multiple times with gB to generate gB-specific T cell lines. These cells were then tested for proliferative responses to gB presented by irradiated PBMC sharing only one DR allele with the responder cells. Cells from the gB-specific lines proliferated only when antigen was presented in the context of a responder DR allele but not when presented in the context of a low responder DR allele. Analysis of immune sera revealed that those from donors with PBMC proliferative responses always contained antibodies reactive with B cell epitopes on both the N-terminal gp93 and C-terminal gp55 portions of gB. In contrast, many of the sera from donors with low gB-specific proliferative responses had gp55-specific antibodies but lacked antibodies to gp93. These results suggest that immunogenetic differences in Th responsiveness to gB may lead to lack of antigen-specific help for antibody responses to gp93 in some cases. The prevalence of these low responder HLA alleles in the population, and the central importance of the T cell response to the generation of antibodies suggest that native gB alone may not be an attractive candidate for an HCMV subunit vaccine.

Molecular analysis of the immune response to human cytomegalovirus glycoprotein B. I. mapping of HLA-restricted helper T cell epitopes on gp93

Human cytomegalovirus (HCMV) is one of the most common causes of congenital infection leading to birth defects, and a leading cause of serious illness in patients with impaired cell-mediated immunity. Helper T cell (Th) responses to HCMV proteins are likely to be important in limiting viral replication and preventing disease. Previous studies from this laboratory have demonstrated that the amino-terminal 513 amino acids of HCMV glycoprotein B (gB) can stimulate both B and T cell responses in humans. In the present study, the proliferative responses of HCMV-specific Th clones to recombinant proteins and synthetic peptides were examined to identify four Th epitopes on gp93, which represents the amino-terminal 460 amino acids of the gB polypeptide. Using clones of known HLA restriction specificity from several donors, it was shown that each HLA class II allele preferentially associates with a different epitope on gB. Five clones from two different donors recognized an epitope in the region of amino acids 250 to 264 restricted by DR4Dw14, two clones from different donors recognized an epitope in the region of amino acids 420 to 434 restricted by DR7Dw17, two clones from different donors recognized an epitope in the region of amino acids 178 to 194 restricted by DQw1 and a single clone recognized an epitope in the region of amino acids 190 to 204 restricted by DPw4. Although all peripheral blood mononuclear cells (PBMCs) expressing a particular HLA class II allele were able to present the appropriate HLA-restricted gB peptide to gB-specific Th clones, not all individuals expressing a given HLA allele exhibited PBMC responses to the corresponding gB peptide. The HLA-related differences in Th recognition of specific epitopes on gB described in this report may have important implications in virus-host interactions and vaccine strategies.

Intravenous lidocaine overdosage in a child.

A six-year-old child inadvertently received an IV solution containing lidocaine HCl. An estimated total dose of 1.2 gm. was administered over approximately an hour. The child had asystole and grand mal seizures associated with lidocaine serum concentration of 19.2 mcg/ml. The pharmacokinetics of lidocaine overdose and treatment are discussed.

Biochemical and immunological analysis of discontinuous epitopes in the family of human cytomegalovirus glycoprotein complexes designated gC-I.

The envelope of human cytomegalovirus contains a family of disulphide-linked glycoprotein complexes designated gC-I which contain two glycoproteins of 52,000 Mr (gp52) and 93,000 to 130,000 Mr (gp93-130). Epitopes recognized by several of our gC-I gp52-specific monoclonal antibodies (MAbs) were previously assigned to three domains based on reactivity with gC-I in a competitive binding assay. In this report, we have used additional gC-I MAbs to characterize three distinct discontinuous epitopes in the gC-I complexes. Two of these epitopes were in Domain I and one in Domain III. These epitopes were resistant to proteolysis, heat denaturation and SDS treatment. However, the discontinuous epitopes were lost after reduction of disulphide bonds. After digestion of gC-I complexes with chymotrypsin, two fragments of 43,000 (43K) Mr and 34,000 (34K) Mr were obtained which contained all discontinuous and continuous epitopes recognized by our gp52 MAbs. The Mr of these fragments could not be reduced further by longer digestion or by use of other proteases such as trypsin or pronase. The 43K fragment contained N-linked oligosaccharides not detected in the 34K fragment. These oligosaccharides may have prevented a complete proteolytic digestion so that the 34K fragment was not always obtained. It was established that 80 to 90% of the mass of these fragments was contributed by gp52. Thus the discontinuous epitopes were composed primarily of gp52 and not gp93-130.

Epstein-Barr virus-transformed lymphoblastoid cell lines as antigen-presenting cells and "augmenting" cells for human CMV-specific Th clones.

The ability of Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) to present human cytomegalovirus (HCMV) antigen to a panel of HCMV-specific T helper (Th) clones was evaluated. Among the seven Th clones studied, only one clone (SP-CN/T3-16) proliferated well to HCMV presented by both autologous mononuclear cells (MNC) and LCL, and one clone (SP-CN/T3-9) proliferated significantly better to HCMV presented by autologous LCL than by autologous MNC. The majority of the HCMV-specific Th clones tested (five out of seven) responded much better to HCMV presented by MNC than to HCMV presented by LCL. The mechanism(s) responsible for the inefficiency of LCL to present HCMV to certain clones was studied. Our results suggested that the defect of LCL is not due to insufficient interleukin 1 production, insufficient MHC class II molecule expression, nor an inhibitory mechanism or factor. In this report, we also demonstrate that by adding a minimum amount of LCL along with MNC as antigen-presenting cells (APC), one can restimulate and expand Th clones much more efficiently than by using MNC alone as APC.