The etiologic agents of varicella and herpes zoster; serologic studies with the viruses as propagated in vitro

Genetic and phenotypic intrastrain variation in herpes simplex virus type 1 Glasgow strain 17 syn+-derived viruses

The Glasgow s17 syn+ strain of herpes simplex virus 1 (HSV1) is arguably the best characterized strain and has provided the reference sequence for HSV1 genetic studies. Here we show that our original s17 syn+ stock was a mixed population from which we have isolated a minor variant that, unlike other strains in the laboratory, fails to be efficiently released from infected cells and spreads predominantly by direct cell-to-cell transmission. Analysis of other s17-derived viruses that had been isolated elsewhere revealed a number with the same release phenotype. Second-generation sequencing of 8 plaque-purified s17-derived viruses revealed sequences that vary by 50 single-nucleotide polymorphisms (SNPs), including approximately 10 coding SNPs. This compared to interstrain variations of around 800 SNPs in strain Sc16, of which a quarter were coding changes. Amongst the variations found within s17, we identified 13 variants of glycoprotein C within the original stock of virus that were predominantly a consequence of altered homopolymeric runs of C residues. Characterization of seven isolates coding for different forms of gC indicated that all were expressed, despite six of them lacking a transmembrane domain. While the release phenotype did not correlate directly with any of these identified gC variations, further demonstration that nine clinical isolates of HSV1 also fail to spread through extracellular release raises the possibility that propagation in tissue culture had altered the HSV1 s17 transmission phenotype. Hence, the s17 intrastrain variation identified here offers an excellent model for understanding both HSV1 transmission and tissue culture adaptation.

Varicella-zoster virus modulates NF-kappaB recruitment on selected cellular promoters

Intercellular adhesion molecule 1 (ICAM-1) expression is down-regulated in the center of cutaneous varicella lesions despite the expression of proinflammatory cytokines such as gamma interferon and tumor necrosis factor alpha (TNF-alpha). To study the molecular basis of this down-regulation, the ICAM-1 induction of TNF-alpha was analyzed in varicella-zoster virus (VZV)-infected melanoma cells (MeWo), leading to the following observations: (i) VZV inhibits the stimulation of icam-1 mRNA synthesis; (ii) despite VZV-induced nuclear translocation of p65, p52, and c-Rel, p50 does not translocate in response to TNF-alpha; (iii) the nuclear p65 present in VZV-infected cells is no longer associated with p50 and is unable to bind the proximal NF-kappaB site of the icam-1 promoter, despite an increased acetylation and accessibility of the promoter in response to TNF-alpha; and (iv) VZV induces the nuclear accumulation of the NF-kappaB inhibitor p100. VZV also inhibits icam-1 stimulation of TNF-alpha by strongly reducing NF-kappaB nuclear translocation in MRC5 fibroblasts. Taken together, these data show that VZV interferes with several aspects of the immune response by inhibiting NF-kappaB binding and the expression of target genes. Targeting NF-kappaB activation, which plays a central role in innate and adaptive immune responses, leads to obvious advantages for the virus, particularly in melanocytes, which are a site of viral replication in the skin.

Ocular Manifestations After Primary Varicella Infection

PURPOSE

To report a case of ocular manifestations after a primary varicella infection.

METHODS

Review of the literature and a case report of a 10-year-old male patient with history of blurry vision and an enlarged pupil 2 months after a varicella infection. Examination revealed uveitis, interstitial keratitis, and internal ophthalmoplegia.

RESULTS

The uveitis resolved with topical steroids; the interstitial keratitis resolved with a faint scar, and the internal ophthalmoplegia persisted.

CONCLUSION

This case report describes a patient with uncommon ocular manifestations after primary varicella.

Thomas Huckle Weller MD: Nobel Laureate and research pioneer in poliomyelitis, varicella-zoster virus, cytomegalovirus, rubella, and other infectious diseases

In 1954, the Nobel Prize for Medicine was awarded to Drs John Enders, Thomas Weller, and Frederick Robbins for their watershed discovery that growth of poliomyelitis virus occurred in cultures of cells of extraneural origin, first reported in 1949. Their demonstration in 1949 that the Lansing type II strain of poliomyelitis could be grown in cultures of human embryonic tissue set into motion a race to develop a vaccine for the disease that had crippled countless thousands of individuals. The discovery and subsequent recognition were only the beginning of a prolific career for Thomas Huckle Weller, who made numerous contributions to the field of virology, including isolating the varicella-zoster virus (VZV) from cases of chickenpox and zoster, providing suggestive evidence that the same virus is responsible for both diseases; isolating the human cytomegalovirus (CMV) for the first time in tissue culture and suggesting the descriptive name now used for it; establishing Coxsackie viruses as the cause of epidemic pleurodynia: and first isolating rubella virus, the cause of German measles. This article presents a brief biography of Dr Thomas Huckle Weller, one of the field's most important figures, with primary focuses on his work on poliomyelitis, varicella-zoster virus, rubella virus, and cytomegalovirus.

Zoster in patients infected with HIV: a review

Varicella-zoster virus (VZV), a member of the human herpesvirus family, causes childhood chickenpox (varicella), becomes latent in sensory ganglia, and reactivates years later in immunocompromised and elderly persons to produce shingles (herpes zoster). Early in the AIDS epidemic, zoster was noted in adults and children infected with HIV. Severe and debilitating zoster-associated dermatological, ophthalmic, and neurological complications may occur in patients infected with HIV. Antiviral therapy can modify the duration of zoster and alleviate its attendant complications. Varicella vaccine may boost the immunity and prevent virus reactivation. VZV immune globulin (VZIG) prevents or modifies clinical illness in persons who have been exposed to varicella or zoster.

The etiologic agents of varicella and herpes zoster; isolation, propagation, and cultural characteristics in vitro

Fourteen strains of virus derived from the cutaneous lesions of cases of varicella and eight from patients with herpes zoster were propagated serially in primary explant cultures of human preputial or embryonic skin-muscle tissue. Infectious material could not be demonstrated in the fluid phase of infected cultures and inocula for passage therefore consisted of suspensions of infected tissue. Such tissue suspensions when stored in the frozen state did not regularly retain infectivity. The cytopathic process was focal and appeared to develop as the result of transfer of infectious material from cell to contiguous cell. Optimum development of the focal lesions in vitro related directly to conditions favoring optimum tissue growth and was further influenced by the spatial relationship of the tissue outgrowth. A variety of types of cells of human origin and several of monkey origin were susceptible to infection and responded with the formation of intranuclear inclusion bodies. The cellular response otherwise was variable, ranging from simple rounding with little change in size to the formation of large multinucleated cytoplasmic syncytia. Strains of virus recovered from patients with varicella and from patients with herpes zoster could not be distinguished on the basis of their cultural attributes.

The etiologic agents of varicella and herpes zoster; isolation, propagation, and cultural characteristics in vitro

Fourteen strains of virus derived from the cutaneous lesions of cases of varicella and eight from patients with herpes zoster were propagated serially in primary explant cultures of human preputial or embryonic skin-muscle tissue. Infectious material could not be demonstrated in the fluid phase of infected cultures and inocula for passage therefore consisted of suspensions of infected tissue. Such tissue suspensions when stored in the frozen state did not regularly retain infectivity. The cytopathic process was focal and appeared to develop as the result of transfer of infectious material from cell to contiguous cell. Optimum development of the focal lesions in vitro related directly to conditions favoring optimum tissue growth and was further influenced by the spatial relationship of the tissue outgrowth. A variety of types of cells of human origin and several of monkey origin were susceptible to infection and responded with the formation of intranuclear inclusion bodies. The cellular response otherwise was variable, ranging from simple rounding with little change in size to the formation of large multinucleated cytoplasmic syncytia. Strains of virus recovered from patients with varicella and from patients with herpes zoster could not be distinguished on the basis of their cultural attributes.

The soluble antigens of varicella-zoster virus produced in tissue culture

It has been found that antigens suitable for routine tests for complement-fixing or precipitating antibodies in the sera of suspected cases of chickenpox or zoster can be readily prepared from tissue cultures of human amnion infected with zostervaricella virus.

Useful antigens were obtained when infected cells were incubated at 36°–38° C. in bovine amniotic fluid diluted with an equal volume of Hanks' solution.

Virus strains gave a good yield of antigen after two or more passages in tissue culture but one strain in its fiftieth passage did not.

Harvested culture fluids require 5- to 20-fold concentration for complement-fixation tests and 100- to 200-fold for precipitation tests; concentration of culture fluids was readily effected by drying from the frozen state after removal of salts by dialysis. Tissue culture antigens gave results by complement-fixation tests which were comparable to those given by a good vesicle fluid.

Some evidence was obtained that the antigens responsible for precipitation were not identical with those fixing complement with convalescent sera.

The varicella vaccine. Vaccine development

In this article, rationales and method of development of attenuated live varicella (Oka) vaccine are described, with biologic and biophysical characteristics of the vaccine virus. The results of early clinical trials in Japan are also described, along with the results of detection of viremia in vaccinees and a follow-up of incidence of zoster in acute leukemic children, which indicate possible immunopathogenesis of varicella and zoster.

Envelopment of varicella-zoster virus: targeting of viral glycoproteins to the trans-Golgi network

Previous studies suggested that varicella-zoster virus derives its final envelope from the trans-Golgi network (TGN) and that envelope glycoproteins (gps) are transported to the TGN independently of nucleocapsids. We tested the hypothesis that gpI is targeted to the TGN as a result of a signal sequence or patch encoded in its cytosolic domain. cDNAs encoding gpI wild type (wt) and a truncated mutant gpI(trc) lacking transmembrane and cytosolic domains were cloned by using the PCR. Cells transfected with cDNA encoding gpI(wt) or gpI(trc) synthesized and N glycosylated the proteins. gpI(wt) accumulated in the TGN, some reached the plasmalemma, but none was secreted. In contrast, gpI(trc) was retained and probably degraded in the endoplasmic reticulum; none was found on cell surfaces, but some was secreted. The distribution of gpI(trc) was not affected by deletion of potential glycosylation sites. To locate a potential gpI-targeting sequence, cells were transfected with cDNA encoding chimeric proteins in which the ectodomain of a plasmalemmal marker, the interleukin-2 receptor (tac), was fused to different domains of gpI. A chimeric protein in which tac was fused with the transmembrane and cytoplasmic domains of gpI was targeted to the TGN. In contrast, a chimeric protein in which tac was fused only with the gpI transmembrane domain passed through the TGN and concentrated in endosomes. We conclude that gpI is targeted to the TGN as a result of a targeting sequence or patch in its cytosolic domain.

Intracellular transport of newly synthesized varicella-zoster virus: final envelopment in the trans-Golgi network

The maturation and envelopment of varicella-zoster virus (VZV) was studied in infected human embryonic lung fibroblasts. Transmission electron microscopy confirmed that nucleocapsids acquire an envelope from the inner nuclear membrane as they enter the perinuclear-cisterna-rough endoplasmic reticulum (RER). Tegument is not detectable in these virions; moreover, in contrast to the mature VZV envelope, the envelope of VZV in the RER is not radioautographically labeled in pulse-chase experiments with [3H]mannose, and it lacks gpI immunoreactivity and complex oligosaccharides. This primary envelope fuses with the RER membrane (detected in cells incubated at 20 degrees C), thereby releasing nucleocapsids to the cytosol. Viral glycoproteins, traced by transmission electron microscopy radioautography in pulse-chase experiments with [3H]mannose, are transported to the trans-Golgi network (TGN) by a pathway that runs from the RER through an intermediate compartment and the Golgi stack. At later chase intervals, [3H]mannose labeling becomes associated with enveloped virions in post-Golgi locations (prelysosomes and plasma membrane). Nucleocapsids appear to be enveloped by wrapping in specialized cisternae, identified as the TGN with specific markers. Tegument-like material adheres to the cytosolic face of the concave surface of TGN sacs; nucleocapsids adhere to this protein, which is thus trapped between the nucleocapsid and the TGN-derived membrane that wraps around it. Experiments with brefeldin A suggest that tegument may bind to the cytosolic tails of viral glycoproteins. Fusion and fission convert the TGN-derived wrapping sacs into an inner enveloped virion and an outer transport vesicle that carries newly enveloped virions to cytoplasmic vacuoles. These vacuoles are acidic and were identified as prelysosomes. It is postulated that secreted virions are partially degraded by their exposure to the prelysosomal internal milieu and rendered noninfectious. This process explains the cell-associated nature of VZV in vitro; however, the mechanism by which the virus escapes diversion from the secretory pathway to the lysosomal pathway in vivo remains to be determined.

Restriction fragment length polymorphism of polymerase chain reaction products from vaccine and wild-type varicella-zoster virus isolates

The nucleotide changes that result in two restriction endonuclease polymorphisms that differentiate wild-type varicella-zoster virus (VZV) from the vaccine strain were determined. Oligonucleotide primers that flank these sites were used to amplify the intervening sequences with the polymerase chain reaction to identify VZV DNA in clinical isolates. Restriction enzyme digestion of the amplification products distinguished vaccine and wild-type genomes from one another. This study confirms the feasibility of amplifying VZV sequences so that they may be detected in clinical specimens and provides a molecular epidemiological approach to strain identification of VZV in vesicular lesions.

Human infection with herpes zoster: etiology, pathophysiology, diagnosis, clinical course, and treatment

Herpes zoster is a cutaneous vesicular eruption resulting from recrudescence of the chickenpox virus. It is mainly a disease of adults, with a predisposition for the elderly or immunocompromised. Although usually localized, the disease can disseminate to visceral organs. Diagnosis is often made based on the characteristic pattern of the lesion and clinical features. Tzanck smear, viral isolation, seroconversion, antibody titers, and monoclonal antibodies may further aid or confirm the diagnosis. Clinical features of herpes zoster may follow a progression through 3 stages, prodromal, acute, and chronic. The prodromal and acute phases seldom require more than symptomatic management. The chronic pain syndrome, postherpetic neuralgia (PHN), demands a more aggressive approach. Pharmacologic intervention, neuroaugmentation, and/or surgery may prevent or alleviate PHN, but universal response to any of these therapeutic approaches is unlikely. Tricyclic antidepressants remain the first choice in treating this pain syndrome. A trial of antiviral therapy may be warranted in patients with disseminated disease or in immunocompromised patients with localized disease. Of the antiviral agents, acyclovir is considered the drug of choice by most clinicians.

Specificity of skin test with varicella-zoster virus antigen in varicella-zoster and herpes simplex virus infections

Specificity of the skin test with varicella-zoster virus (VZV) antigen was examined in guinea pigs infected with herpes simplex virus (HSV) type 1 or VZV and in children with a history of HSV infection who developed varicella. Infected guinea pigs responded positively only to homologous virus. No cross-reaction between HSV and VZV was detected in the skin test, as well as in the neutralization test in infected guinea pigs, suggesting that the VZV skin test is specific for immunity to VZV infection. Twelve children were infected with HSV during an HSV epidemic and subsequently developed varicella in institutional settings. During the 2.5-month period between the HSV and VZV infections, the immune status of the children to VZV was negative both in the skin test and in the antibody test, although antibody to HSV was detected by an immune adherence hemagglutination test. After VZV infection, all responded positively both in the skin test and in the antibody test (immune adherence hemagglutination test) to VZV. These results suggest that the VZV skin test is specific for immunity to VZV infection, not cross-reactive to HSV infection in humans. This specificity will be of value in screening susceptibility or immunity to VZV, irrespective of prior HSV infection.

The potency determination of human varicella-zoster immunoglobulin by enzyme-linked immunosorbent assay, complement-fixation test and indirect fluorescent antibody tests

Traditionally, plasma for the production of the human varicella-zoster immunoglobulin (VZIG) has been selected on the basis of the complement-fixing antibody (CFA) titre. Since immune individuals may lack CFA to varicella-zoster virus (VZV), non-CFA may be of importance in protection. In a search for a simple and reliable method for potency determination, 24 VZIG preparations were quantified by enzyme-linked immunosorbent assay (ELISA), the complement-fixation test (CFT), the indirect fluorescent antibody test to acetone-fixed (IF) and viable (FAMA) VZV-infected cells, respectively. The antibody titres obtained by the various methods were compared. Arranged in order of decreasing agreement, the correlation coefficients (r) of the regression equations between the variables were 0.62 for CFT and FAMA, 0.50 for CFT and ELISA and 0.26 for CFT and IF in a log2 plot. There was complete agreement between the titres obtained by the commercially available Enzygnost Varicella/Zoster kits (Behring Institute, Marburg, F.R. Germany) and the ELISA microtitre plates produced at our institute (r = 1). The regression equation lines for ELISA/CFT and FAMA/CFT titres tended to be parallel to each other, while the line for IF/CFT titres had a less steep slope. Similar titration curves were obtained for VZIGs fractionated by two different methods. Furthermore, the titration curves of serum pools from varicella and zoster convalescents, respectively, had a similar shape below delta OD = 0.4. Generally, a steeper slope was observed above delta OD = 0.4. As antibody detectable by ELISA seems to correlate with protection and the method is sensitive, specific, reproduceable, simple to carry out and easily automated, it may be suitable for the potency determination of VZIGs.

Differentiation of members of the human herpesviridae family by radioimmunoassay

Many individuals who are seronegative for one member of the human Herpesviridae family are strongly seropositive for other members. Using sera from such individuals, the radioimmunoassay technique demonstrated absence of antigen-antibody cross-reactions between varicella-zoster virus (VZV) and herpes simplex virus (HSV) at levels of less than one part in 1,000. Sera containing antibody to both HSV and VZV were absorbed with antigens of one agent without significantly altering the amount of remaining antibody to the other antigen. This further suggests that HSV and VZV do not share a common antigen. The same radioimmunoassay technique and serum absorption method that revealed no serological cross-reactions between HSV and VZV revealed the expected cross-reaction between HSV type 1 (HSV-1) and HSV-2. Reciprocally absorbed anti-HSV-1 and anti-HSV 2 sera were able to differentiate the two HSV types reliably. No cross-reactions were seen between cytomegalovirus, VZV, and HSV or between Epstein-Barr virus, VZV, and HSV. We postulate that heterotypic antibody responses sometimes observed for VZV after primary infections by HSV may not be due to shared antigens, but to activation of latent VZV infections, release of new VZV antigens, and consequent stimulation of new antibody production to VZV.

Antibody responses to varicella-zoster virus and the role of antibody in host defense

Antibody titers to varicella-zoster (VZ) virus in persons aged 1-85 years were measured. Through age 50, the percent of seropostitive individuals continued to rise. There was no fall in geometric mean titer with aging, and there may have been an increase in VZ antibody titer in older persons. Thus, a fall in VZ antibody with increasing age does not seem likely to account for the increased incidence of zoster in the elderly. Similarly, immunocompromised patients who are more likely to develop zoster than normals did not have lower VZ antibody titers than normal persons. Finally, immunocompromised persons with disseminated zoster had antibody titers that were somewhat higher that those of immunocompromised persons with localized zoster. It appears that humoral immunity has little or no influence on either the development or the course of herpes zoster.

Prophylaxis of varicella in high-risk children: dose-response effect of zoster immune globulin

Immunodeficient patients who were presumed to be susceptible received zoster immune globulin prophylaxis after exposure to varicella. The highest clinical attack rate (35.9%) was seen in household contacts; the lowest attack rate (0%) was observed in children exposed at school. Among household contacts, 48 of 100 patients who received high titer ZIG (reciprocal complement fixation titer greater than or equal to 2,560) developed fourfold rises in serum CF antibody between pre- and 48-hour post-treatment specimens, compared to only one of 34 patients treated with lower titer ZIG lots (P less than 0.001). Patients who developed fourfold antibody rises were significantly less likely to contract clinical varicella (P less than 0.01). Patients who received high titer ZIG also had significantly lower risks of death (P = 0.025) and complications (P = 0.006). Among ZIG-treated patients who contracted clinical varicella, 80% developed mild disease (less than 100 pox), and the median incubation period was prolonged. Immunodeficient children exposed to varicella benefit from ZIG prophylaxis and higher titer ZIG is of greatest benefit.

Cell-mediated immunity to varicella-zoster virus measured by virus inactivation: mechanism and blocking of the reaction by specific antibody

The process whereby varicella-zoster (V-Z) virus is inactivated in vitro by immune human peripheral blood leukocytes stimulated with V-Z antigen was examined. It was found that stimulation of leukocytes by V-Z antigen, but not by other viral antigens, was required for inactivation of V-Z virus to occur. Viral inactivation could be blocked by addition of V-Z antiserum to either the stimulation phase of the reaction or the inactivation phase, further demonstrating the specificity of the reaction. In addition these blocking experiments suggested that modulation of V-Z membrane antigen by antiserum occurred with an accompanying loss of immunological recognition of virus-infected cells. Inactivation of V-Z virus in vitro in this study appeared not to be dependent upon the secretion of interferon or upon antibody-dependent cellular cytotoxicity. The specific cells required for V-Z inactivation were T lymphocytes and monocytes (macrophage precursors).

Specific immunoglobulin responses after varicella and herpes zoster

The indirect immunofluorescence technique has been used to titrate the specific immunoglobulins in 200 sera from 64 patients with varicella, and 195 sera from 67 patients with herpes zoster. IgG and IgM antibodies were detected in all patients with varicella, and IgA in 59 (92%). All three classes of antibody appeared 2--5 days after the onset of the rash, increased virtually simultaneously and reached maximum titres during the second and third weeks. IgG then declined slowly, but never became undetectable and was still present in five subjects who were retested after 2--4 years; it was present in 88 out of 100 healthy young adults and probably persists indefinitely after varicella. IgA and IgM antibodies declined more rapidly and were not detected in specimens taken more than a year after the illness. IgA, however, may possibly persist in some cases since low titres were found in 8 out of 88 young adults who possessed IgG antibody and had presumably had varicella in the past. IgA responses were significantly weaker in children under the age of 6 years than in older children and adults. Six out of 67 patients with zoster were tested at various times before the onset of the rash: IgG antibody was detected in all. IgG was present in all sera taken after the onset of the rash, increased rapidly after 2--5 days, reached maximum titres during the second and third weeks and then declined slowly. IgA antibody was detected in 66 patients (99%) and IgM in 52 (78%); both types of antibody followed transient courses, as in varicella. Maximum titres of IgG and complement-fixing antibodies were greater after zoster than after varicella, but the differences were not significant. IgA and IgM titres in young adults with zoster were significantly lower than in older patients, and also lower than in young adults with varicella. Increases in varicella-zoster antibody in patients with herpes simplex virus infections consisted mainly of IgG, sometimes IgA, but never IgM.

Quantitation of antibodies to varicella-zoster virus by immune adherence hemagglutination

Immune adherence hemagglutination was compared with the complement fixation test as a means of measuring antibodies to varicella-zoster virus. Analysis of acute- and convalescent-phase sera from patients infected with varicella-zoster or with herpes simplex virus showed the immune adherence hemagglutination test to be more sensitive than the complement fixation test, and greater cross-reactivity between the two viruses appeared to be associated with the increased sensitivity. The two assay methods were used to measure antibodies to varicella-zoster virus in 265 sera obtained from patients of different ages as well as sera from 26 patients with leukemia. There were 35 cases where antibodies were detected by immune adherence hemagglutination but not by complement fixation, whereas in five cases the converse was found. Our findings support the contention that immune adherence hemagglutination is the method of choice for detecting antibodies to varicella-zoster virus.

Prophylaxis of varicella in children with neoplastic disease: comparative results with zoster immune plasma and gamma globulin

The incidence and severity of varicella following a close family contact were evaluated in children with neoplastic diseases who received prophylaxis either with commerical gamma globulin or with zoster immune plasma, as compared to patients who did not receive any prophylaxis. In the untreated group, all 14 patients developed varicella, complicated by 1 case of encephalitis and 2 cases of fatal pneumonia. In the group of 17 patients who received 0.6-1.2 ml/kg body weight of gamma globulin, 16 developed varicella, complicated by pneumonia in 2 cases, with 1 death. In the third group of 27 patients who received 10 ml/kg body weight of zoster immune plasma (ZIP), obtained from healthy adults convalescing from herpes zoster, there were only 8 cases of varicella, all very mild. Thus, prophylaxis with ZIP significantly reduced the incidence of clinical varicella (p less than 0.01) and attenuated the severity of its course.

Neutralization tests with varicella-zoster virus

A technique for neutralization tests using varicella-zoster virus propagated in primary human thyroid cells is described. The level of neutralizing antibody following chickenpox does not usually exceed a titre of 1/40 and in adults many years after infection it may be very low. After zoster a much higher and more persistent antibody response occurs. Contact with chickenpox also produced a rise in neutralizing antibody in one out of the five patients tested. One case who had had chickenpox but not zoster had a high level of neutralizing antibody and the possible reasons for this are discussed. No cross-neutralization with Herpes simplex virus was demonstrated but the rise in titre of complement-fixing antibody to HS occurring in herpetic subjects with chickenpox (Ross et al. 1965) was confirmed. Two samples of human gamma-globulin were shown to have high levels of neutralizing antibody to V-Z virus and one was known to have been found effective clinically.

We are indebted to Dr R. E. Hope-Simpson for the paired contact sera and also for many valuable discussions in the course of this work. We would also like to thank Dr D. Taylor-Robinson who collected the paired zoster sera, Dr R. M. Rawcliffe and Dr F. Whitwell who arranged the supply of thyroid tissue, and Dr G. C. Turner and Dr J. Eller for the samples of human gamma-globulin. We are grateful to Mrs M. Stewart for valuable technical assistance.

The growth of varicella-zoster virus in tissue fragments

V-Z virus has been propagated in embryonic human skin, lung and kidney grafted on the chorio-allantois of hens' eggs or maintained as organ cultures in vitro. The histological changes produced resemble those in the intact human host and the virus produced is cell-free as it is in vesicle fluid. It is suggested that organ cultures may provide a useful model for investigating virus synthesis but the method has not been found practical for the large scale production of cell-free virus in the laboratory.