Intracerebroventricular delivery of glucocerebrosidase reduces substrates and increases lifespan in a mouse model of neuronopathic Gaucher disease.

Gaucher disease is caused by a deficit in the enzyme glucocerebrosidase. As a consequence, degradation of the glycolipids glucosylceramide (GluCer) and glucosylsphingosine (GluSph) is impaired, and their subsequent buildup can lead to significant pathology and early death. Type 1 Gaucher patients can be treated successfully with intravenous replacement enzyme, but this enzyme does not reach the CNS and thus does not ameliorate the neurological involvement in types 2 and 3 Gaucher disease. As one potential approach to treating these latter patients, we have evaluated intracerebroventricular (ICV) administration of recombinant human glucocerebrosidase (rhGC) in a mouse model of neuronopathic Gaucher disease. ICV administration resulted in enzyme distribution throughout the brain and alleviated neuropathology in multiple brain regions of this mouse model. Treatment also resulted in dose-dependent decreases in GluCer and GluSph and significantly extended survival. To evaluate the potential of continuous enzyme delivery, a group of animals was treated ICV with an adeno-associated viral vector encoding hGC and resulted in a further extension of survival. These data suggest that ICV administration of rhGC may represent a potential therapeutic approach for type 2/3 Gaucher patients. Preclinical evaluation in larger animals will be needed to ascertain the translatability of this approach to the clinic.

High and sustained transgene expression in vivo from plasmid vectors containing a hybrid ubiquitin promoter.

Sustained transgene expression will be required for the successful treatment of most genetic diseases being considered for gene therapy. The initially high levels of expression attained with plasmid DNA (pDNA) vectors containing viral promoters, such as that from cytomegalovirus (CMV), decline precipitously to near-background levels within two to three weeks. Here we constructed pDNA vectors containing the human cellular UBB (encoding ubiquitin B; Ub) promoter and evaluated their expression in the mouse lung. Cationic lipid-pDNA complexes were instilled intranasally (IN) or injected intravenously (IV) into immunodeficient BALB/c mice. Chloramphenicol acetyltransferase (CAT) reporter gene expression from the UBB promoter was initially very low at day 2 post-administration, but by day 35 exceeded the level of expression attained from a CMV promoter vector by four- to ninefold. Appending a portion of the CMV enhancer 5' of the UBB promoter (CMV-Ub) increased CAT expression to nearly that of the CMV promoter and expression persisted in the lung for at least 3 months, with 50% of day 2 levels remaining at day 84. In the liver, expression from the CMV-Ub hybrid promoter was sustained for 42 days. As previous studies have shown that eliminating immunostimulatory CpG motifs in pDNA vectors reduces their toxicity, we constructed a CpG-deficient version of the CMV-Ub vector expressing alpha-galactosidase A, the enzyme deficient in Fabry disease, a lysosomal storage disorder. After IN or IV administration, levels of alpha-galactosidase A from this vector were not only undiminished but increased 500% to 1500% by day 35. Our results indicate that CpG-reduced plasmid vectors containing a CMV-Ub hybrid promoter may provide the long-term expression required for a practical gene therapeutic.

Increased duration of transgene expression in the lung with plasmid DNA vectors harboring adenovirus E4 open reading frame 3.

For gene therapy to be effective in the treatment of chronic diseases, plasmid DNA (pDNA) vectors that provide persistent expression of therapeutic levels of the transgene product are desirable. Studies in the lung with adenovirus vectors showed that products of the adenovirus E4 region can act both in cis and in trans to increase the duration of expression when transcription of the transgene was under the control of the human cytomegalovirus (CMV) promoter. To determine if these E4-encoded proteins could also effect greater persistence of expression from a nonviral vector, a complex composed of cationic lipid GL-67, a CMV promoter plasmid (pCF1-CAT), and an E4-containing adenovirus vector (Ad2/betagal-4) was instilled into the lungs of BALB/c nu/nu mice. Significant increases in the duration of transgene expression were observed for up to 10 weeks postinstillation compared with expression from mice instilled with control complexes containing an adenovirus vector deleted of most of E4 (Ad2/betagal-2). This effect could also be observed in immunodeficient NIH-rnu rats as well as in immunocompetent BALB/c mice. Studies with CMV promoter mutants indicated that a region proximal to the promoter was necessary for the E4-mediated increase in longevity of expression. In addition to the CMV promoter, a CMV enhancer-human mucin I (MUC-I) hybrid promoter also responded to these E4-encoded proteins with increased persistence of transgene expression, but a human interleukin 8 (IL-8) promoter did not. Ad2/betagal-4 could be replaced by a pDNA vector expressing only the E4 region, indicating that products of the E4 region alone were sufficient in the absence of expression from the rest of the adenovirus genome. Further analysis indicated that the protein encoded by open reading frame 3 (ORF3) alone was sufficient for conferring the increase in persistence of expression. These data indicate that expression of a single protein from the adenovirus genome can significantly improve the duration of transgene expression from pDNA vectors, and increases the feasibility of using nonviral vectors for the treatment of chronic diseases.

Correction of enzymatic and lysosomal storage defects in Fabry mice by adenovirus-mediated gene transfer.

Fabry disease is a recessive, X-linked disorder caused by a deficiency of the lysosomal hydrolase alpha-galactosidase A. Deficiency of this enzyme results in progressive deposition of the glycosphingolipid globotriaosylceramide (GL-3) in the vascular lysosomes, with resultant distension of the organelle. The demonstration of a secretory pathway for lysosomal enzymes and their subsequent recapture by distant cells through the mannose 6-phosphate receptor pathway has provided a rationale for somatic gene therapy of lysosomal storage disorders. Toward this end, recombinant adenoviral vectors encoding human alpha-galactosidase A (Ad2/CEHalpha-Gal, Ad2/CMVHIalpha-Gal) were constructed and injected intravenously into Fabry knockout mice. Administration of Ad2/CEHalpha-Gal to the Fabry mice resulted in an elevation of alpha-galactosidase A activity in all tissues, including the liver, lung, kidney, heart, spleen, and muscle, to levels above those observed in normal animals. However, enzymatic expression declined rapidly such that by 12 weeks, only 10% of the activity observed on day 3 remained. Alpha-galactosidase A detected in the plasma of injected animals was in a form that was internalized by Fabry fibroblasts grown in culture. Such internalization occurred via the mannose 6-phosphate receptors. Importantly, concomitant with the increase in enzyme activity was a significant reduction in GL-3 content in all tissues to near normal levels for up to 6 months posttreatment. However, as expression of alpha-galactosidase A declined, low levels of GL-3 reaccumulated in some of the tissues at 6 months. For protracted treatment, we showed that readministration of recombinant adenovirus vectors could be facilitated by transient immunosuppression using a monoclonal antibody against CD40 ligand (MR1). Together, these data demonstrate that the defects in alpha-galactosidase A activity and lysosomal storage of GL-3 in Fabry mice can be corrected by adenovirus-mediated gene transfer. This suggests that gene replacement therapy represents a viable approach for the treatment of Fabry disease and potentially other lysosomal storage disorders.

Optimization of plasmid vectors for high-level expression in lung epithelial cells.

Nonviral gene therapy approaches use a plasmid vector to express the desired transgene. We have systematically examined several regulatory elements within plasmid vectors that govern gene expression, e.g., the promoter, enhancer, intron, and polyadenylation signal, by constructing a series of plasmids that differed only in the particular sequence element being evaluated. Of the several promoters and polyadenylation signal sequences that were tested, the human cytomegalovirus (CMV) immediate early gene promoter and the addition of polyadenylation signal sequences from the bovine growth hormone (BGH) gene or rabbit beta-globin gene produced the highest levels of expression in vitro. The inclusion of a hybrid intron 3 to the promoter further increased expression 1.6-fold. The addition of a region of the CMV enhancer 5' to several weak promoters increased expression 8- to 67-fold, and co-transfection with a second plasmid encoding a chimeric transcription factor also enhanced expression. On the basis of these results, the CMV promoter, the hybrid intron, and the BGH polyadenylation signal were selected for consistent high level expression in vitro and in the mouse lung. However, expression was transient, with greater than 60% loss of activity in the first 7 days. This transient expression was not specific to CMV promoter-containing plasmids, because plasmids containing other heterologous promoters showed a similar profile of transient expression in vivo. These comparative analyses begin to provide a basis for the development of optimized expression plasmids for gene therapy of lung diseases.

HIV-1 gp120 Effects on Signal Transduction Processes and Cytokines: Increased src-Family Protein Tyrosine Kinase Activity.

Varying degrees of neurological dysfunction are observed in AIDS patients who develop AIDS dementia complex (ADC). Data from a large number of in vivo and in vitro rodent studies have suggested a role for the HIV envelope glycoprotein gp 120 in this process. These studies were initiated to clarify possible effects of recombinant gp120 on signal transduction systems and the synthesis of specific ADC-related cytokines in human neuroblastoma cells. Out results indicate that gp120 on signal transduction systems and the synthesis of specific ADC-related cytokines in human neuroblastoma cells. Our results indicate that gp120 did not induce the synthesis of cAMP, IPs or NO, nor did it alter agonist-induced synthesis of these molecules. In addition, it did not induce the synthesis of IL-6 and TNFα. However, it did activate a src-family protein tyrosine kinase which phosphorylates several substrates, including prominent proteins in the 115 and 60 kDa range. This gp120-induced tyrosine phosphorylation may contribute to neurological dysfunction since protein tyrosine kinases are known to be involved in processes important for pre- and post-synaptic neuronal function.

Detailed analysis of structures and formulations of cationic lipids for efficient gene transfer to the lung.

Cationic lipid-mediated gene transfer of cystic fibrosis transmembrane conductance regulator (CFTR) cDNA represents a promising approach for treatment of cystic fibrosis (CF). Here, we report on the structures of several novel cationic lipids that are effective for gene delivery to the lungs of mice. An amphiphile (#67) consisting of a cholesterol anchor linked to a spermine headgroup in a "T-shape" configuration was shown to be particularly efficacious. An optimized formulation of #67 and plasmid vector encoding chloramphenicol acetyl-transferase (CAT) was capable of generating up to 1 microgram of CAT enzyme/lung following intranasal instillation into BALB/c mice. This represents a 1,000-fold increase in expression above that obtained in animals instilled with naked pDNA alone and is greater than 100-fold more active than cationic lipids used previously for CFTR gene expression. When directly compared with adenovirus-based vectors containing similar transcription units, the number of molecules of gene product expressed using lipid-mediated transfer was equivalent to vector administration at multiplicities of infection ranging from 1 to 20. The level of transgene expression in the lungs of BALB/c mice peaked between days 1 and 4 post-instillation, followed by a rapid decline to approximately 20% of the maximal value by day 7. Undiminished levels of transgene expression in the lung could be obtained following repeated intranasal administration of #67:DOPE:pCF1-CAT in nude mice. Transfection of cells with formulations of #67:DOPE:pCF1-CFTR generated cAMP-stimulated CFTR chloride channel and fluid transport activities, two well-characterized defects associated with CF cells. Taken together, the data demonstrate that cationic lipid-mediated gene delivery and expression of CFTR in CF lungs is a viable and promising approach for treatment of the disease.

C-type natriuretic peptide neuromodulates via "clearance" receptors.

A recently discovered endogenous autacoid, C-type natriuretic peptide, was tested in a pheochromocytoma (PC12) cell line for effects on 1) catecholamine release induced by a depolarizing stimulus, 2) guanylyl and adenylyl cyclase activities, and 3) specific 125I-labeled atrial natriuretic peptide (ANP) binding. C-type natriuretic peptide suppressed evoked neurotransmitter release in the absence of guanylyl cyclase activation or adenylyl cyclase inhibition; however, both a "clearance" (ANP-C) receptor binding agent, des-[Gln18Ser19Gly20Leu21Gly22]-ANF-(4-23)-NH2 (cANF), and pertussis toxin prevented this neuromodulatory effect. The C-type natriuretic peptide preferentially bound to receptors that also bound cANF. The results suggest that C-type natriuretic peptide suppressed evoked neurotransmitter efflux by binding to ANP-C receptors coupled to a pertussis toxin-sensitive process; furthermore, the neuromodulatory effect of C-type natriuretic peptide occurred independently of guanylyl cyclase activation or adenylyl cyclase inhibition. The novel aspects of these findings are 1) neuromodulatory effects of C-type natriuretic peptide, 2) guanylyl cyclase-independent actions of C-type natriuretic peptide, and 3) ANP-C receptors mediating C-type natriuretic peptide actions.

Neuromodulatory effects of atrial natriuretic peptides correlate with an inhibition of adenylate cyclase but not an activation of guanylate cyclase.

We reported previously that atrial natriuretic factor (ANF) and the ANF clearance receptor binding peptide, C-ANF(4-23)-NH2 (C-ANF), inhibit catecholamine (CA) release from rat, nerve growth factor-treated pheochromocytoma cells (PC12 cells) by a guanylate cyclase independent mechanism. This mechanism is most likely a pertussis toxin (PTX)-sensitive inhibition of adenylate cyclase. This study examines the role of the second messengers, cyclic AMP (cAMP) and cyclic GMP (cGMP), in mediating atrial natriuretic factor effects on depolarization-induced CA release from PC12 cells. The following evidence supports the hypothesis that the neuromodulatory action of atrial peptides is independent of increases in cGMP: 1) ANF does not potentiate the inhibitory effect of C-ANF on CA release or cAMP generation but still elevates cGMP concentrations in the presence of C-ANF; 2) the neuromodulatory effects of ANF and C-ANF are blocked or reversed by a membrane permeable analog of cAMP, dibutyryl cAMP; 3) ANF and C-ANF attenuate CA release in the presence of a maximally effective concentration of dibutyryl cGMP; 4) the inhibitory effect of dibutyryl cGMP is PTX-insensitive whereas the atrial peptide effect is blocked by PTX-pretreatment; and 5) dibutyryl cGMP is without effect on adenylate cyclase. These data are consistent with the hypothesis that ANF and C-ANF act via the ANF clearance (R2) receptor to suppress adenylate cyclase activity and neurotransmission.

Neuromodulatory effects of atrial natriuretic factor are independent of guanylate cyclase in adrenergic neuronal pheochromocytoma cells.

This study tests the hypothesis that atrial natriuretic factor (ANF) and C-ANF(4-23)-NH2 (C-ANF) augment cGMP generation and inhibit both cAMP generation and depolarization-induced catecholamine release in nerve growth factor treated pheochromocytoma cells by a pertussis toxin (PTX)-sensitive mechanism. Synthetic rat ANF(99-126) and the clearance receptor antagonist C-ANF (10(-12)-10(-9) M) inhibited basal and 5 microM vasoactive intestinal peptide (VIP)-induced cAMP generation in a concentration-dependent manner. These actions of ANF and C-ANF were blocked by 12-18 h pretreatment with PTX (100 ng/ml), suggesting ANF receptor coupling to adenylate cyclase via an inhibitory guanine nucleotide-binding protein. Both ANF (10(-11)-10(-9) M) and C-ANF (10(-11)-10(-8) M) also inhibited K(+)-induced catecholamine release in a concentration-dependent manner. ANF (10(-11)-10(-8) M) increased cGMP generation in a concentration-dependent manner but C-ANF did not. The accumulation of cGMP in response to ANF was not altered by treatment with PTX. Therefore, PTX dissociated the increased concentrations of cGMP from the ANF-mediated depression of evoked catecholamine release. C-ANF also dissociated elevations in cGMP concentrations from an ANF-mediated attenuation of evoked catecholamine release. The results of this study indicate that ANF inhibits adrenergic neurotransmission independent of guanylate cyclase.

Cyclic guanosine 3',5' monophosphate mediates the inhibitory effect of atrial natriuretic factor in adrenergic, neuronal pheochromocytoma cells.

This study tests the hypothesis that atrial natriuretic factor (ANF) inhibits catecholamine release from rat pheochromocytoma cells by increasing levels of intracellular cyclic GMP (cGMP). Rat differentiated pheochromocytoma cells are a model of adrenergic nerves and allow the exploration of the effects of various hormones, autacoids, drugs and neuromodulators on adrenergic neurotransmission in cell culture. Synthetic rat ANF (99-126) inhibited K+-induced norepinephrine and dopamine release, as measured by high-performance liquid chromatography, in a concentration-dependent manner over the concentration range of 10(-11) to 10(-8) M. ANF stimulated intracellular cGMP accumulation, as measured by specific radioimmunoassay, in a concentration-dependent manner over the same concentration range. The cGMP analog, N2-2'-O-dibutyryl cGMP also inhibited K+-induced norepinephrine and dopamine release in a concentration-dependent manner. The results of this study are consistent with the hypothesis that ANF acts as an inhibitory neuromodulator in adrenergic nerves via the second messenger, cGMP.

Loss of functional voltage-gated sodium channels in persistent mumps virus-infected PC12 cells.

Rat pheochromocytoma (PC12) cells, persistently infected with mumps virus (MV), failed to generate full-sized stimulus-evoked action potentials (SEAPs) when examined by intracellular electrophysiological recording techniques. Application of tetrodotoxin (TTX) had little or no effect on MV-reduced SEAPs, indicating that the number of functional voltage-gated Na+ channels was decreased or their operation was blocked by the virus. In contrast, MV-infected cells generated normal Ca2+ spikes when bathed in a solution containing TTX, tetraethylammonium ions and a high concentration (20 mM) of Ca2+. In addition, when infected cells bathed in TTX were superfused with Co2+ the SEAP profile reverted to that typical of PC12 cells with functional voltagegated K+ channels only. These observations indicate that MV affects voltage-gated Na+ channels, but spares voltage-gated Ca2+ and K+ channels of persistently infected cells.

Thromboxane synthesis and actions in isolated adrenergic nerve (pheochromocytoma-12) cells.

The synthesis of cyclooxygenase products by cultured adrenergic neuronal (pheochromocytoma-12) cells was investigated by measuring both the extent of conversion of [3H]arachidonic acid to prostanoids and the immunoreactive prostanoid concentrations in the bathing buffer. Statistically significant amounts of arachidonic acid metabolites migrated with prostaglandins (PGs) E (81 +/- 14 fmol) and F (68 +/- 13 fmol) and thromboxane B (49 +/- 12 fmol) on thin-layer chromatography plates after incubation of differentiated cells with 1 pmol of [3H]arachidonic acid. The conversion of arachidonic acid to these products was lower in undifferentiated cells, although PGE- and PGF-like metabolites were produced in significant amounts. Both immunoreactive PGE and thromboxane B were detected in the media of differentiated cells and their concentrations were elevated when the cells were exposed to arachidonic acid. The potential significance of the thromboxane production by pheochromocytoma-12 cells was investigated by examining the effect of a stable thromboxane mimetic, U46619, on potassium-stimulated norepinephrine release. The U46619 significantly enhanced norepinephrine release from potassium-depolarized cells. These results are indicative of PGE, PGF and thromboxane production by isolated adrenergic neuronal tissue. A thromboxane receptor agonist also was observed to potentiate norepinephrine release.

Mumps virus-induced alterations in cellular excitability during persistent infections.

Persistent mumps virus infections were established in rat pheochromocytoma (PC-12) and human medulloblastoma (TE-671) continuous cell lines. Significant amounts of infectious virus were produced by the PC-12 cells; infectious virus production by the TE-671 cells was limited. This restricted replication may be due to decreased production of viral envelope glycoproteins by TE-671 cells. The presence of virus changed the distribution of stimulus-evoked electrical responsiveness of both cell lines from responsiveness composed primarily of normal, rapidly rising, all-or-nothing action potentials to one dominated by abnormal, slowly rising, graded responses or by no response at all. Such changes have the potential to disrupt neural integration within the nervous system, and suggest a new mechanism by which persistent virus infections might play a role in chronic neurological and/or mental disease.

Mapping and cloning of a fla-che region of the Rhizobium meliloti chromosome.

We constructed a genetic map of the fla-che region of the Rhizobium meliloti chromosome using cotransduction with bacteriophage phi M12. Several other chromosomal markers located in the general area are included in the map. We isolated plasmids carrying wild-type DNA inserts that complement the mapped mutations from a genomic library carried in the broad-host-range vector pLAFR1. The complementation data obtained from the clones confirmed the contransduction map and clarified the exact order of several of the behavioral genes. A restriction map of this area was developed by using the cloned DNA. One of the five individual EcoRI fragments subcloned from the original clones complemented two of the behavioral mutations.

Analysis of anthranilic acid by liquid chromatography.

Analytical methods for the assay of anthranilic acid and for determination of the impurities methyl anthranilate, anthranoylanthranilic acid and 3- and 4-aminobenzoic acid are described. A Microbondapak C18 column is used for both the assay and the impurity determination. The assay is based on isocratic development with a mobile phase of 35:65 v v methanol/pH-3 phosphate buffer, with benzoic acid as internal standard. The impurities are separated by gradient elution. The standard deviation of the assay method is about 1% and the limit of detection for the impurities is about 0.01%.

Analysis of the herpes simplex virus genome during in vitro latency in human diploid fibroblasts and rat sensory neurons.

We have previously designed in vitro model systems to characterize the herpes simplex virus type 1 (HSV-1) genome during in vitro virus latency. Latency was established by treatment of infected human embryo lung fibroblast (HEL-F) cells or rat fetal neurons with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and was maintained by increasing the incubation temperature after inhibitor removal. Virus was reactivated by reducing the incubation temperature. We have now examined the HSV-1-specific DNA content of latently infected HEL-F cells and rat fetal neurons treated with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and increased temperature. The HEL-F cell population contained, on an average, between 0.25 and 0.5 copies of most, if not all, HSV-1 HindIII and XbaI DNA fragments per haploid cell genome equivalent. In contrast, the latently infected neurons contained, on an average, 8 to 10 copies per haploid cell genome equivalent of most HSV-1 BamHI DNA fragments. There was no detectable alteration in size or molarity of the HSV-1 terminal or junction DNA fragments obtained by HindIII, XbaI, or BamHI digestion of the latently infected neuron or HEL-F cell DNA, as compared with digestion of a reconstruction mixture of purified HSV-1 virion and HEL-F cell DNAs. These data suggest that the predominant form of the HSV-1 genome in either latently infected cell population is nonintegrated, linear, and nonconcatameric.

Inability of various immune mechanisms to establish in vitro latent infection in sensory neurons infected by HSV-1. Brief report.

Various immune mechanisms were tested for their ability to alter a normally productive infection of herpes simplex virus in cultures of dissociated rat sensory neurons. These mechanisms included anti-HSV antibody with and without the aid of complement, HSV-sensitized "T" cells, natural killer cells, and "K" cells plus anti-HSV antibody (ADCC reactions). Although both anti-HSV antibody plus complement and the ADCC mechanism significantly limited infectious HSV production, no mechanism was capable of preventing the eventual infection of the majority of neurons. It appears, therefore, that none of these mechanisms by themselves can convert a normally productive infection of sensory neurons in culture to a non-productive or latent infection.

Herpes simplex virus latency and reactivation in isolated rat sensory neurons.

An in vitro herpes simplex virus type 1 (HSV-1) latency model has been established using neurons isolated from dissociated rat fetus sensory ganglia as the host cell. Rat fetal neuron cells were pretreated for 24 hr at 37 degrees with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon, infected with HSV-1 (approximately 2.5 plaque-forming units/cell), and treated for 7 days with the same inhibitor combination. Infectious HSV-1 became undetectable 3 days postinfection and remained undetectable during the remainder of the inhibitor treatment. After removal of inhibitors on day 7, infectious virus remained undetectable for 2-7 days; subsequently, virus replication ensued and neuronal cells were destroyed. Incubation of inhibitor-treated, infected neuron cells at 40.5 degrees after removal of inhibitors resulted in extension of the latent period to at least 15 days. HSV-1 was reactivated from latently infected neurons by reducing the incubation temperature from 40.5 to 37 degrees and virus-specific cytopathology was observed in neurons within 96 hr after reducing temperature. This in vitro model system will provide the first system to analyze, in a primary cell type of neuronal origin, the state of the HSV genome during establishment and maintenance of the latent state and during virus reactivation.

Effects of lectins on peripheral infections by herpes simplex virus of rat sensory neurons in culture.

Concanavalin A and wheat germ agglutinin are capable of preventing a productive peripheral infection of dissociated rat sensory neurons in culture by herpes simplex virus type 1. Concanavalin A binds to the herpes simplex virion, rendering it inactive, whereas wheat germ agglutinin binds to the peripheral neuritic extensions of the sensory neurons, rendering them incapable of initiating a productive viral infection. This latter effect (i) seems to be specific for wheat germ agglutinin since other lectins have no effect, (ii) is not the result of cellular cytotoxicity, (iii) is dependent on an N-acetylneuraminic acid moiety, and (iv) may be due either to viral receptor site masking or to binding of wheat germ agglutinin to the neuritic receptor molecule for herpes simplex virus.