ZIKV infection regulates inflammasomes pathway for replication in monocytes

ZIKV causes microcephaly by crossing the placental barrier, however, the mechanism of trans-placental dissemination of ZIKV remains unknown. Here, we sought to determine whether monocytes, which can cross tissue barriers, assist ZIKV dissemination to the fetus. We determined this by infecting monocytes with two strains of ZIKV: South American (PRVABC59) and Nigerian (IBH30656) and analyzing viral replication. We found that ZIKV infects and replicates in monocytes and macrophages, which results in the modulation of a large number of cellular genes. Analysis of these genes identified multiple pathways including inflammasome to be targeted by ZIKV, which was confirmed by analyzing the transcript levels of the proteins of inflammasome pathways, NLRP3, ASC, caspase 1, IL-1 and IL-18. Interestingly, IFNα and the IFN inducible gene, MxA were not enhanced, suggesting prevention of innate antiviral defense by ZIKV. Also, inhibition of inflammasome led to an increased transcriptional activity of IFNα, MxA and CXCL10. Based on these results we suggest that ZIKV transcription is regulated by inflammasomes.

Methodological issues in weight cycling

Recent studies have suggested that weight changes may be related to disease risk independent of weight status. A critical step in testing this assertion is the measurement of weight change and so-called "weight cycling". However intuitive the concept of weight cycling may appear, research in this area is hampered by complex methodological issues. This article discusses various measures of nominal weight cycling, including the standard deviation, coefficient of variation, regression techniques, and cycles. A cycle is a sequence of a gain followed by a loss or vice versa. The various measures are compared in seven hypothetical cases created to illustrate their strengths and weaknesses. Superior performance of the cycles measure over the coefficient of variation, number of fluctuations, and simple regression methods is argued. The linkage of the cycles measure with the statistical theory of runs also provides a basis for testing the significance of weight fluctuations or other variables that may cycle, such as blood lipids, etc. The cycles measure and runs test provide a viable definition for identifying weight cycling and a tool for evaluating the critical amount of weight gained and/or lost in relationship to risk.

Characterization of an antisense transcript spanning the UL81-82 locus of human cytomegalovirus

In this study we present the characterization of a novel transcript, UL81-82ast, UL81-82 antisense transcript, and its protein product. The transcript was initially found in a cDNA library of monocytes from a seropositive donor. mRNA was obtained from monocytes isolated from a healthy donor with a high antibody titer against human cytomegalovirus (HCMV). The mRNAs were cloned into a lambda phage-derived vector to create the cDNA library. Using PCR, UL81-82ast was amplified from the library. The library was tested for the presence of numerous HCMV genes. Neither structural genes nor immediate-early genes were found. UL81-82ast was detected in five bone marrow samples from healthy antibody-positive donors. This same transcript was also found in in vitro-infected human fibroblasts early after infection but disappears at the same time that UL82 transcription begins. Not only was the transcript amplified using reverse transcription-PCR and sequenced but its protein product (UL82as protein) was detected by both Western blot and immunofluorescence. Phylogenetic studies using UL82as protein were conducted, showing a high degree of conservation in clinical isolates, laboratory strains of HCMV, and even in chimpanzee CMV. The transcript could be involved in the posttranscriptional regulation of the UL82 gene, affecting its mRNA stability or translation. Since the UL82 product, pp71, functions as an immediate-early transactivator, its posttranscriptional control could have some effect over latency reactivation and lytic replication.

Phylogenetic relationships of dengue-1 viruses from Argentina and Paraguay

We sequenced the Capsid-pre Membrane (C/prM) and the Envelope-Nonstructural protein 1 (E/NS1) regions of 24 recent isolates of dengue-1 (DEN-1) from South America. This included 12 Argentinean and 11 Paraguayan DEN-1 strains isolated in 2000 plus a Paraguayan strain isolated in 1988. These sequences were compared with published sequences of DEN-1 isolated worldwide to determine the origin of these isolates. Pairwise comparisons of strains from Paraguay and Argentina revealed a nucleotide divergence of 0-5% in the E/NS1 region and 0-3% in the C/prM region. Our results showed that these viruses belong to the same genotype, but can be separated into two clades. Interestingly, both clades circulated simultaneously in the same geographic area during the 2000 outbreaks. Amino acid differences were found between both clades in the C/prM region at position 100 (Lys vs. Arg) and in the E/NS1 region at positions 722 (Ala vs. Thr). Although the geographic movement of DEN-1 virus can not be unequivocally traced from the genetic relationship determined here, our results suggest that the recent epidemics in Argentina and Paraguay were due to the re-emergence of a previously circulating strain, or to the virus circulating unnoticed, rather than to the introduction of a new genotype.

In vitro infection of megakaryocytes and their precursors by human cytomegalovirus

Apart from congenital human cytomegalovirus (HCMV) infection, manifest HCMV disease occurs primarily in immunocompromised patients. In allogeneic bone marrow transplantation, HCMV is frequently associated with graft failure and cytopenias involving all hematopoietic lineages, but thrombocytopenia is the most commonly reported hematologic complication. The authors hypothesized that megakaryocytes (MK) may be a specific target for HCMV. Although the susceptibility of immature hematopoietic progenitors cells to HCMV has been established, a productive viral life cycle has only been linked to myelomonocytic maturation. The authors investigated whether HCMV can also infect MK and impair their function. They demonstrated that HCMV did not affect the thrombopoietin (TPO)-driven proliferation of CD34(+) cells until MK maturation occurred. MK challenged with HCMV showed a 50% more rapid loss of viability than mock-infected cells. MK and their early precursors were clearly shown to be susceptible to HCMV in vitro, as evidenced by the presence of HCMV in magnetic column-purified CD42(+) MK and 2-color fluorescent staining with antibodies directed against CD42a and HCMV pp65 antigen. These findings were confirmed by the infection of MK with a laboratory strain of HCMV containing the beta-galactosidase (beta-gal) gene. Using chromogenic beta-gal substrates, HCMV was detected during MK differentiation of infected CD34(+) cells and after infection of fully differentiated MK. Production of infectious virus was observed in cultures infected MK, suggesting that HCMV can complete its life cycle. These results demonstrate that MK are susceptible to HCMV infection and that direct infection of these cells in vivo may contribute to the thrombocytopenia observed in patients infected with HCMV. (Blood. 2000;95:487-493)

Diet controversies in lipid therapy

Increasing awareness of the relationship between diet and disease has prompted a notable increase in nutrition research. The focus of many of these studies continues to be on amount and type of fat in the diet. At the same time, a great deal of attention is being directed at other dietary components and their mode of action. The results are promising. More definitive answers must await future clinical trial data. However, the total dietary approach, including compliance measures, remains the foundation on which other nutrition recommendations should be based.

Apoptosis induced by human cytomegalovirus infection can be enhanced by cytokines to limit the spread of virus

Fas-mediated apoptosis is one of the immune effector pathways leading to the elimination of virus infected cells. In vivo, apoptotic signals are delivered to virus infected cells by Fas-L and other cytokines secreted by specific T lymphocytes. Cellular immune response appears to be essential in prevention of human cytomegalovirus (HCMV) disease. We have hypothesized that HCMV infection might directly or indirectly result in upregulation of Fas receptor and in the presence of Fas ligand, lead to apoptosis of infected cells. We show that infection of human fibroblasts with HCMV is associated with upmodulation of Fas-R process that could be further potentiated by interferon (IFN-gamma). Using DNA agarose gel electrophoresis, terminal dideoxy transferase reaction, and annexin assay, we demonstrated that in a productive HCMV infection of human fibroblasts, loss of cell viability was not only due to virus-mediated cell lysis but also to due to apoptosis. IFN-gamma induced relative HCMV resistance and prevented loss in cell viability. In contrast, anti-Fas monoclonal antibody CH11, serving as Fas agonist, resulted in an accelerated loss in viability of infected cells. IFN-gamma in combination with CH11 further increased the rate of apoptosis and compared to cultures with CH11 only, this effect was not restricted to only infected cells. While IFN-gamma did not affect the number of cells expressing immediate early antigen, it markedly reduced structural protein expression. IFN-gamma in combination with CH11, decreased the expression of HCMV matrix protein pp65, reduced the amount of HCMV DNA and infectious virus produced. Our results are consistent with the theory that cells infected with HCMV can be eliminated by immune effector cells via Fas-mediated apoptosis. IFN-gamma, in addition to its intrinsic antiviral activity, primes HCMV infected cells to the action of Fas ligand and Fas-mediated apoptosis.

Identification of persistent RNA-DNA hybrid structures within the origin of replication of human cytomegalovirus

Human cytomegalovirus (HCMV) lytic-phase DNA replication initiates at the cis-acting origin of replication, oriLyt. oriLyt is a structurally complex region containing repeat elements and transcription factor binding sites. We identified two site-specific alkali-labile regions within oriLyt which flank an alkali-resistant DNA segment. These alkali-sensitive regions were the result of the degradation of two RNA species embedded within oriLyt and covalently linked to viral DNA. The virus-associated RNA, vRNA, was identified by DNase I treatment of HCMV DNA obtained from sucrose gradient purified virus. This heterogeneous population of vRNA was end labeled and used as a hybridization probe to map the exact location of vRNAs within oriLyt. vRNA-1 is localized between restriction endonuclease sites XhoI at nucleotide (nt) 93799 and SacI at nt 94631 and is approximately 500 bases long. The second vRNA, vRNA-2, lies within a region which exhibits a heterogeneous restriction pattern located between the SphI (nt 92636) and BamHI (nt 93513) and is approximately 300 bases long. This region was previously shown to be required for oriLyt replication (D. G. Anders, M. A. Kacica, G. S. Pari, and S. M. Punturieri, J. Virol. 66:3373-3384, 1992). RNase H analysis determined that vRNA-2 forms a persistent RNA-DNA hybrid structure in the context of the viral genome and in an oriLyt-containing plasmid used in the transient-replication assay.

Generation of a nude mouse tumor model for in vivo replication of human cytomegalovirus

Human cytomegalovirus (HCMV) is a common opportunistic infection resulting in retinitis in 15%-40% of AIDS patients. Several anti-HCMV therapies are currently available, and new treatments are in various stages of development. An HCMV animal model involving in vivo infection of human cells without the dependence on human fetuses or multiple surgical procedures has been developed. A human glioblastoma cell line that is permissive for HCMV replication (U373MG) was adapted to grow as a subcutaneous tumor in nude mice. These tumors arise in approximately 7 days and grow progressively. An evaluation of HCMV DNA replication demonstrated an increase in the accumulation of HCMV DNA within infected tumors from 48 to 168 h after infection. Immunohistochemical analysis showed focal areas of HCMV infection in which expression of immediate-early and late antigens was detected. In addition, it was demonstrated that ganciclovir inhibited HCMV DNA replication in vivo in a dose-dependent manner.

Physical activity, genetic, and nutritional considerations in childhood weight management

Almost one-quarter of U.S. children are now obese, a dramatic increase of over 20% in the past decade. It is intriguing that the increase in prevalence has been occurring while overall fat consumption has been declining. Body mass and composition are influenced by genetic factors, but the actual heritability of juvenile obesity is not known. A low physical activity (PA) is characteristic of obese children and adolescents, and it may be one cause of juvenile obesity. There is little evidence, however, that overall energy expenditure is low among the obese. There is a strong association between the prevalence of obesity and the extent of TV viewing. Enhanced PA can reduce body fat and blood pressure and improve lipoprotein profile in obese individuals. Its effect on body composition, however, is slower than with low-calorie diets. The three main dietary approaches are: protein sparing modified fast, balanced hypocaloric diets, and comprehensive behavioral lifestyle programs. To achieve long-standing control of overweight, one should combine changes in eating and activity patterns, using behavior modification techniques. However, the onus is also on society to reduce incentives for a sedentary lifestyle and over-consumption of food. To address the key issues related to childhood weight management, the American College of Sports Medicine convened a Scientific Roundtable in Indianapolis.

Spread of human cytomegalovirus (HCMV) after infection of human hematopoietic progenitor cells: model of HCMV latency

Clinical experience and laboratory data suggest that human cytomegalovirus (HCMV) is present in peripheral blood of seropositive individuals in a latent or persistent state and can be transmitted via blood products and be reactivated in seropositive immunocompromised patients. The pathophysiology of HCMV latency and the nature of HCMV interaction with hematopoietic cells remains unknown. In this study, we investigated the infection of bone marrow (BM) progenitor cells and their progeny as a model of HCMV latency. A clinical isolate and the recombinant laboratory strain Towne/lox containing the Escherichia coli beta galactosidase (beta-gal) gene regulated by immediately early (IE) HCMV promoter were used to infect highly purified CD34+ cells. Although the infection of these cells with a clinical isolate was associated with an inhibition of proliferation by 59%, an expansion of progeny derived from these cells was possible. Polymerase chain reaction analysis and staining for beta-gal have shown that HCMV persisted in infected BM CD34+ cells and their progeny for up to 4 weeks. However, IE and late gene products (mRNA and protein) were detected only late in the course of infection and their expression correlated with terminal macrophage differentiation of the CD34+-derived progeny. Although early infection of CD34+ progenitor cells was not productive (as shown by the plaque assay), infectious virus could be recovered from the terminally differentiated cultures. BM progenitor cells may serve as a reservoir of the latent virus with limited transcription. Proliferation and monocytic maturation of infected progenitors may lead to the numerical expansion of HCMV-infected cells, which serve as a source of HCMV dissemination and reactivation.

Human cytomegalovirus alters interleukin-6 production by endothelial cells

In an effort to study whether human cytomegalovirus (HCMV) can disrupt the balanced cytokine network that controls human hematopoiesis, we investigated the ability of a laboratory strain HCMV (AD169) to alter the production of interleukin-6 (IL-6) by cultured endothelial cells (HUVECs). ECs are important components of human bone marrow stroma and produce factors that stimulate the proliferation and differentiation of human hematopoietic progenitors. HCMV was able to greatly increase production of both mRNA and protein for IL-6 in unprimed HUVECs. When we discriminated between viral pellet and cleared viral supernatants, the supernatants induced an increase in mRNA at 30 minutes and protein by 2 hours, whereas an increase in IL-6 caused by virus itself did not become evident until 12 hours. The possibility that IL-6 induction was simply caused by the presence in the viral stock of endotoxin, IL-1 alpha, IL-1 beta, tumor necrosis factor alpha, or IL-4, all known inducers of IL-6 in HUVECs, was ruled out by the addition of polymyxin B and appropriate neutralizing antibodies. These findings show that HCMV is capable of directly and indirectly modulating the production by HUVECs of IL-6, one of the cytokines involved in the process of hematopoiesis.

Infection of mononucleated phagocytes with human cytomegalovirus

Human cytomegalovirus (HCMV) can be isolated from peripheral blood leukocytes; however, in vitro, only abortive infection of monocytes, lymphocytes, and granulocytes has been detected. These studies demonstrate that freshly isolated monocytes can be infected with HCMV. Infection of monocytes was not associated with loss of cell viability. The virus replication cycle in monocytes resembled that observed in fibroblasts but the virus yield was approximately 0.1% of that observed in fibroblasts. Transient phenotypical changes occurred in HCMV-infected monocytes. Virus persists in infected monocytes upon differentiation to macrophages, suggesting that monocytes may serve as a carrier of HCMV and a vector for viral dissemination. Differentiated mononuclear phagocytes appear to support a productive HCMV infection. Using a recombinant HCMV strain to express beta-galactosidase, we were able to transduce the bacterial beta-galactosidase gene into monocytes and macrophages.

Suppression of normal human hematopoiesis by cytomegalovirus in vitro

Human cytomegalovirus (HCMV) infection is associated with marrow suppression in immunocompromised patients. To examine the mechanism(s) underlying this suppression, the effect of a laboratory strain of HCMV (AD169) and a clinical isolate of HCMV on colony formation by normal human marrow (BMC) hematopoietic progenitors in the presence and/or absence of monocyte/macrophages (MO) and T cells was studied. Direct addition of HCMV at multiplicity of infection (MI) of 0.1 to 5 to BMC produced dose-dependent inhibition of colony forming unit-mix (CFU-Mix) (30-82%), CFU granulocyte, macrophage (CFU-GM) (15-98%), and burst forming unit-erythroid (BFU-E) (23-86%); no consistent effect of CFU-erythroid (CFU-E) was noted. This inhibition occurred both with the direct addition of HCMV to the culture plates as well as by the preincubation of BMC with HCMV followed by washing of the cells; significant inhibition (p < 0.01) of colony formation occurred after 1 hour of incubation at MI of 5. No suppression of colony formation occurred when UV-irradiated virus was used. The inhibitory effect of HCMV was reduced when MO and T cells were removed prior to exposure of marrow to virus at MI of 1 to 5. At MI of 20, however, HCMV suppressed colony formation by BMC depleted of MO and T cells by about 40%. Coculture of autologous or allogeneic T cells, but not MO, exposed to HCMV with intact or depleted marrow resulted in inhibition of CFU-Mix (51%), CFU-GM (40%), and BFU-E (37%). The inhibitory effect of virus-exposed T cells did not appear to be mediated through a soluble factor. T cells expressing CD8 antigen were most active in this process; natural killer (NK) cells were not active. These results suggest that the suppressive effect of HCMV on hematopoiesis may be mediated in part through T lymphocytes.

Enhancement of deoxyguanosine kinase activity in human lung fibroblast cells infected with human cytomegalovirus

Studies were conducted to establish the relationship between deoxyguanosine kinase activity and human cytomegalovirus (HCMV) infection. Using both PAGE and isoelectric focusing techniques, extracts from untreated and infected cells were examined for deoxyguanosine kinase activity. The analyses resulted in identical migration rates for deoxyguanosine kinase activity in both infected and uninfected extracts. These data and kinetic studies based on apparent Km values suggest that HCMV enhanced a cellular kinase activity rather than coded for a virus specific enzyme. Furthermore, our results indicated that infected cells, like normal fibroblasts, contain two deoxyguanosine kinase activities, one of mitochondrial and another of cytosolic origin. Of particular interest was the observation that HCMV infection caused an enhancement of the mitochondrial enzymatic activity while the cytosolic activity showed no change. Deoxycytidine kinase activity which is associated with cytosolic deoxyguanosine kinase was unaffected by HCMV infection.

Isolation of infectious bovine rhinotracheitis virus from the soft-shelled tick, Ornithodoros coriaceus

Infectious bovine rhinotracheitis virus was isolated from the soft-shelled tick (Ornithodoros coriaceus). Serological identification of the isolated viruses was confirmed by restriction endonuclease digestion of purified virus DNA. These isolations indicate that the soft-shelled tick may be a vector for infectious bovine rhinotracheitis virus. This may be the first reported isolation of mammalian herpesvirus from an arthropod vector.

Analysis of human cytomegalovirus nucleoprotein complexes

When chromatin was isolated from cells infected with human cytomegalovirus, the virus DNA remained with the chromatin fraction. If deproteinized virus DNA was added to either isolated nuclei or chromatin, the DNA was lost during the chromatin isolation. When isolated chromatin from cytomegalovirus-infected cells was banded in isopycnic metrizamide gradients, a single peak with a density of 1.18 g/cm3 was present. Analysis of this peak in isopycnic neutral CsCl gradients indicated that it contained both human cytomegalovirus and human embryonic lung cell DNAs. When infected nuclei were treated with micrococcal nuclease, 11S subunit particles which cosedimented with cell nucleosomes and contained virus DNA were isolated.

Transcription of the human cytomegalovirus genome in productively infected cells

Nuclear and cytoplasmic RNAs, synthesized in cells productively infected with human cytomegalovirus (HCMV) were analysed at various times after infection by liquid and filter DNA-RNA hybridization. Results of these experiments have revealed that: (i) the fraction of the genome transcribed increased as infection progressed. In the nucleus, transcripts represented approx. 20% of the virus DNA sequences at both 2 and 4 h post-infection (p.i.) and 36% of the virus DNA at 40 h p.i; (ii) the increase in virus sequences among nuclear transcripts at late times was prevented by the DNA synthesis inhibitor, 2'-deoxyfluorouridine; (iii) early virus RNA transcripts were subset of those represented in late RNA; (iv) two classes of early RNA were identified by competition hybridization; (v) approx. 10% of the late nuclear transcripts were symmetrical. Results of filter hybridization at DNA excess indicated that virus-specific RNA represented 0.6% of RNA labelled from 0 to 2 h p.i., and 1.8% of RNA labelled from 28 to 30 h. Polyadenylated RNA isolated from cytoplasm represented 1.2% and 10% of labelled mRNA at 2 h and 30 h respectively. Our data show that during productive infection of human cells by HCMV, gene expression is under temporal, quantitative and post-transcriptional control.

Hypocholesterolemic effect of yogurt and milk

In order to determine the effect of milk products on serum cholesterol, triglycerides, and diet, 54 volunteers were studied for varying periods with dietary supplementation of nonpasteurized yogurt, pasteurized yogurt and 2% butterfat milk. Serum cholesterol was significantly reduced by 5 to 10% after 1 week of supplementation with either nonpasteurized or pasteurized yogurt; 2% butterfat milk reduced serum cholesterol to a smaller and less significant effect. Serum triglycerides were unaffected by the diet and dietary intake studies confirmed that intake of other nutrients remained relatively stable throughout the study. Supplementation of diet with yogurt may have a helpful hypocholesterolemic effect.

Partial characterization of a herpes-type virus (K9V) derived from Kaposi's sarcoma

A herpes-type virus that was originally isolated from a cell culture (designated K9V) derived from a tumor biopsy specimen from a patient with Kaposi's sarcoma was partially characterized. The host range of K9V, as determined by the induction of virus-specific cytopathology, synthesis of antigens, and plaque formation, was limited to human cells and particularly to fibroblasts. Immunofluorescence and complement fixation assays confirmed the specificity of the presence of cytomegalovirus (CMV)-type antigens in K9V-infected human fibroblasts. In addition, the density of K9V DNA was consistent with the density of CMV DNA. However, some peculiarities were observed in the K9V strain of CMV. The virus seemed more cell-associated in human fibroblasts than were known laboratory strains: The spread of cytopathology was slow and did not always involve the whole cell sheet, and the total regression of cytopathology with the establishment of a persistent infection was common. Similar characteristics have recently been observed in the Mj strain of CMV, which has been shown to be oncogenic in human fibroblasts.

Comparison of the polypeptides of several strains of human cytomegalovirus

Analysis of purified human cytomegalovirus (CMV) by sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed 32 polypeptides with mol. wt. ranging from 13,500 to 235,000. Similar analysis of purified preparations of four strains of CMV showed a remarkable similarity in polypeptide composition. Results indicate that the four strains may be related.

Persistence of cytomegalovirus in human lymphoblasts and peripheral leukocyte cultures

The in vitro susceptibility of human peripheral lymhpocytes and lymphoblastoid (F265) cells to infection by human cytomegalovirus was examined. Infection of these cell types with cytomegalovirus resulted in a persistent type of infection rather than the typical growth curve observed with permissive fibroblastic cells. When infection of peripheral lymphocytes was associated with a blastogenic response, the virus persisted for a longer time and at a higher titer than in cells in which a blastogenic response did not occur. Autoradiographic studies and infectious-center assays indicated that only a small number of cells, resembling lymphocytes, were involved in virus persistence. Whether or not the persistence of the virus indicates release of input virus or synthesis or new virus was not determined.

The development by cytomegalovirus-infected cells of binding affinity for normal human immunoglobulin

After infection with human cytomegalovirus (CMV), cells develop an affinity for normal human immunoglobulin G (IgG). This was demonstrated using 125iodine-labeled purified IgG. It was further demonstrated that the immunoglobulin molecule binds to CMV-infected cells via its Fc portion, and competition for binding to infected cells occurred between purified preparations of human IgG and the Fc fragment of human IgG. Whole sera from individuals with or without a high titer of anti-CMV antibody were labeled with 125iodine and it was demonstrated that serum from individuals with no anti-CMV antibody had an affinity for CMV-infected cells which probably reflected binding of IgG via its Fc fragment. The possible significance of these results in immunologic studies of human CMV is considered.

Cytomegalovirus: conversion of nonpermissive cells to a permissive state for virus replication

Human embryonic kidney cells are epithelioid cells which are normally nonpermissive for in vitro replication of human cytomegalovirus. These cells were converted to a permissive state for the virus by prior treatment with 5-iodo-2'-deoxyuridine. When this method was used, a nonpermissive cell was made permissive to an infecting virus.

Cytomegalovirus replication in cells pretreated with 5-iodo-2'-deoxyuridine

The replication of human cytomegalovirus (CMV) in cells pretreated with 5-iodo-2'-deoxyuridine (IUdR) was studied. Pretreatment of cells with IUdR enhanced several parameters of virus replication. Virus grown in drug-treated cells exhibited a shorter eclipse period and the cells produced more infectious virus sooner than did untreated cells. There was an approximate fivefold increase in virus yield per cell in the drug-treated samples when compared to control cultures. The time required for plaque development was shortened by 6 days in drug-treated cultures. Pretreatment of cells with IUdR also increased plaquing efficiency of the virus by approximately 10-fold. The enhancement of virus replication by IUdR was further demonstrated by varying the multiplicity of infection. In a 7-day period there was a 100-fold increase in sensitivity of the cultures for virus detection when the cells had been previously exposed to IUdR. The data presented indicate the possibility that IUdR interferes with the production of a cellular product inhibitory for CMV replication.