Differential growth of human enteric adenovirus 41 (TAK) in continuous cell lines

Adenovirus Infection of Human Enteroids Reveals Interferon Sensitivity and Preferential Infection of Goblet Cells

Human adenoviruses (HAdV) are significant human pathogens. Although only a subset of HAdV serotypes commonly cause gastroenteritis in humans, most HAdV species replicate in the gastrointestinal tract. Knowledge of the complex interaction between HAdVs and the human intestinal epithelium has been limited by the lack of a suitable cell culture system containing relevant cell types. Recently, this need has been met by the stable and prolonged cultivation of primary intestinal epithelial cells as enteroids. Human enteroids have been used to reveal novel and interesting aspects of rotavirus, norovirus, and enterovirus replication, prompting us to explore their suitability for HAdV culture. We found that both prototype strains and clinical isolates of enteric and nonenteric HAdVs productively replicate in human enteroids. HAdV-5p, a respiratory pathogen, and HAdV-41p, an enteric pathogen, are both sensitive to type I and III interferons in human enteroid monolayers but not A549 cells. Interestingly, HAdV-5p, but not HAdV-41p, preferentially infected goblet cells. And, HAdV-5p but not HAdV-41p was potently neutralized by the enteric human alpha-defensin HD5. These studies highlight new facets of HAdV biology that are uniquely revealed by primary intestinal epithelial cell culture.IMPORTANCE Enteric adenoviruses are a significant cause of childhood gastroenteritis worldwide, yet our understanding of their unique biology is limited. Here we report robust replication of both prototype and clinical isolates of enteric and respiratory human adenoviruses in enteroids, a primary intestinal cell culture system. Recent studies have shown that other fastidious enteric viruses replicate in human enteroids. Therefore, human enteroids may provide a unified platform for culturing enteric viruses, potentially enabling isolation of a greater diversity of viruses from patients. Moreover, both the ability of interferon to restrict respiratory and enteric adenoviruses and a surprising preference of a respiratory serotype for goblet cells demonstrate the power of this culture system to uncover aspects of adenovirus biology that were previously unattainable with standard cell lines.

Inefficient export of viral late mRNA contributes to fastidiousness of human adenovirus type 41 (HAdV-41) in 293 cells

The human adenovirus (HAdV) early protein E1B55K interacts with E4orf6 to form an E3 ubiquitin ligase complex, which plays key roles in virus replication. To illustrate the reason for the fastidiousness of HAdV-41 in 293 cells, interaction between heterotypic E1B55K and E4orf6 proteins was investigated. HAdV-5 E1B55K could interact with HAdV-41 E4orf6, and vice versa. To form E1B55K/E4orf6 E3 ubiquitin ligase, HAdV-41 E4orf6 recruited Cul2 while HAdV-5 E4orf6 interacted with Cul5. The ligase complex formed by HAdV-5 E1B55K and HAdV-41 E4orf6 could cause the degradation of p53 and Mre11. However, in E1-deleted HAdV-41-infected 293TE7 cells, which expressed HAdV-41 E1B55K, viral late mRNAs were exported from nucleus more efficiently and accumulated to a higher concentration in cytoplasm when compared with that in infected 293 cells. These results suggested that interaction between homotypic E1B55K and E4orf6 was indispensable for efficient export of viral late mRNAs.

High frequency of cultivable human subgroup F adenoviruses in stool samples from a paediatric population admitted to hospital with acute gastroenteritis

The family Adenoviridae consists of five genera of which the genus Mastadenovirus includes human viruses classified into 57 serotypes clustered into seven subgroups (A–G). Serotypes 40 and 41 (subgroup F) are specifically associated with childhood gastroenteritis and are the most common cause of acute gastroenteritis in young children after rotaviruses and noroviruses. Standard methods for laboratory diagnosis of adenovirus infection include electron microscopy (EM) and conventional cell culture (CCC), although it is widely considered that adenoviruses 40 and 41 are difficult to cultivate, such that their circulation is most likely underestimated. One hundred and ten faecal specimens from paediatric patients with gastroenteritis were confirmed positive for adenovirus by EM and/or CCC at the Virology Unit of the University Hospital of Parma, Italy, during the period January 2010–December 2012. They were analysed to determine the actual prevalence of adenovirus 40 and 41 in these patients using PCR and restriction endonuclease analysis, and to evaluate their ability to be cultivated in standard cell lines. The results showed a high prevalence of subgroup F (62.7 %), with serotype 41 (89.8 %) predominating over serotype 40 (10.2 %). Surprisingly, among the 75 adenoviruses isolated by CCC, 37 (49 %) belonged to subgroup F, suggesting a higher capacity of adenovirus 40 and 41 to replicate in cell culture than previously thought. PCR and restriction enzyme techniques provide an efficient means of diagnosing enteric adenoviruses correctly, including subgroup F adenovirus strains in young children with gastroenteritis.

Short-fiber protein of ad40 confers enteric tropism and protection against acidic gastrointestinal conditions

The lack of vectors for selective gene delivery to the intestine has hampered the development of gene therapy strategies for intestinal diseases. We hypothesized that chimeric adenoviruses of Ad5 (species C) displaying proteins of the naturally enteric Ad40 (species F) might hold the intestinal tropism of the species F and thus be useful for gene delivery to the intestine. As oral-fecal dissemination of enteric adenovirus must withstand the conditions encountered in the gastrointestinal tract, we studied the resistance of chimeric Ad5 carrying the short-fiber protein of Ad40 to acid milieu and proteases and found that the Ad40 short fiber confers resistance to inactivation in acidic conditions and that AdF/40S was further activated upon exposure to low pH. In contrast, the chimeric AdF/40S exhibited only a slightly higher protease resistance compared with Ad5 to proteases present in simulated gastric juice. Then, the biodistribution of different chimeric adenoviruses by oral, rectal, and intravenous routes was tested. Expression of reporter β-galactosidase was measured in extracts of 15 different organs 3 days after administration. Our results indicate that among the chimeric viruses, only intrarectally given AdF/40S infected the colon (preferentially enteroendocrine cells and macrophages) and to a lesser extent, the small intestine, whereas Ad5 infectivity was very poor in all tissues. Additional in vitro experiments showed improved infectivity of AdF/40S also in different human epithelial cell lines. Therefore, our results point at the chimeric adenovirus AdF/40S as an interesting vector for selective gene delivery to treat intestinal diseases.

Novel recombinant adenovirus type 41 vector and its biological properties

BACKGROUND

Human adenovirus serotype 41 (Ad41) is a natural pathogen of the digestive tract and can cause gastroenteritis. There has been interest in reconstructing Ad41 as a gene delivery vector targeting the gastrointestinal tract, which is hampered by its fastidiousness.

METHODS

An Ad41 E1B55K-transduced 293 cell line (293E12) was established as the packaging cell line. A backbone plasmid (pAdbone41) and a shuttle plasmid (pSh41-CMV) were constructed based on the Ad41 genome. Replication-defective adenovirus (Ad41-GFP) was rescued in 293E12 after being transfected with the linearized adenoviral plasmid, which was generated by homologous recombination of pAdbone41 and the shuttle plasmid carrying the GFP gene in Escherichia coli strain BJ5183. The packaging ability of 293E12, the stability of the Ad41-GFP genome and the acid-resistant property of Ad41-GFP were all investigated.

RESULTS

A 293E12 cell could produce approximately 9000 viral particles of Ad41-GFP, which is close to the amount in the control virus (Ad5-GFP) amplified in one 293 cell. Ad41-GFP contained a genetically stable genome after being passaged eight times in 293E12 cells. More significantly, Ad41-GFP was more resistant to acid exposure than Ad5-GFP. It retained almost complete viability when exposed to hydrochloric acid with a pH value of 2 for 30 min, whereas Ad5-GFP lost 99% of its viability under the same conditions. Ad41-GFP was also more tolerant to treatment with artificial digestive fluid.

CONCLUSIONS

An Ad41 vector system was successfully constructed, which consisted of the backbone plasmid, shuttle plasmid and packaging cell line 293E12. This system can be utilized to generate genetically stable and acid-resistant recombinant Ad41 carrying any gene of interest.

Prevalence and characterization of enteric adenoviruses in the South of Ireland

Enteric adenoviruses have been shown to be a substantial cause of pediatric gastroenteritis in various parts of the world, and are considered to be the second most common cause of viral gastroenteritis, next to rotavirus in young children. Genetic characterization of 95 adenovirus isolates obtained from patients with acute gastroenteritis between 2002 and 2007 from the southern regions of Ireland, were characterized by PCR analysis, restriction endonuclease (RE) analysis and sequencing analysis. All isolates were found to be of adenovirus type 41 origin. Genetic analysis of seven hypervariable regions (HVRs) located within the hexon gene has revealed a high level of amino acid sequence homology in samples over the course of this study, with a very close relationship to the D22 genome type. The D22 genome type has been detected in several other countries, thus suggesting Irish isolates have common genome types with other stains worldwide. This is the first such study undertaken in the south of Ireland, to type and genetically characterize adenoviral gastroenteritis isolates, and has revealed a high level of conservation within the isolated analyzed.

Novel adenovirus vaccine vectors based on the enteric-tropic serotype 41

Replication-defective adenovirus vectors, primarily developed from serotype 5 (Ad5) viruses, have been widely used for gene transfer and vaccination approaches. Vectors based on other serotypes of adenovirus could be used in conjunction with, or in place of, Ad5 vectors. In this study, Ad41, an enteric adenovirus usually described as 'non-cultivable' or 'fastidious,' has been successfully cloned, rescued and propagated on 293-ORF6 cells. The complementation capabilities of this cell line allow generation of Ad41 vectors at titers comparable to those obtained for Ad5 vectors. Mice immunized with an Ad41 vector containing an HIV envelope (Env) gene mounted anti-Env cellular and humoral immune responses. Ad41-Env vectors appear to be particularly attractive when used in heterologous prime-boost regimens, where they induce significantly higher cellular immune responses to HIV-Env than Ad5-based regimens. Ad41-based constructs are attractive vaccine vectors alone or in combination with Ad5 adenovectors, since each vector type can provide circumvention of pre-existing immunity to the other.

293T cells expressing simian virus 40 T antigen are semi-permissive to bovine adenovirus type 3 infection

Human cells do not normally support productive bovine adenovirus type 3 (BAdV-3) infection. Here, the outcome of BAdV-3 infection of both 293 cells and 293 cells modified to constitutively express the simian virus 40 (SV-40) T antigen (293T cells) was studied. Whereas BAdV-3 could efficiently infect 293 cells, there was a block in virus DNA replication, late-gene expression and virus production. In contrast, replication and efficient virus production could be detected in 293T cells infected with BAdV-3 or transfected with a replication-competent genomic BAdV-3 clone (pFBAV304). Early-phase gene expression was detected readily in both BAdV-3-infected 293 and 293T cells. However, the progression to efficient viral DNA synthesis and late-phase protein synthesis occurred only in 293T cells. Electron microscopy and virus growth kinetics demonstrated the formation of progeny virus in 293T cells. The SV-40 T antigens act to overcome a barrier in BAdV-3 DNA replication in 293 cells.

Characterizations of adenovirus type 41 isolates from children with acute gastroenteritis in Japan, Vietnam, and Korea

Genetic and antigenic characterizations of 70 strains of adenovirus type 41 (Ad41), isolated between 1998 and 2001 from children in Japan, Vietnam, and Korea, were done by DNA restriction enzyme (RE) analysis, sequencing analysis, and monoclonal antibody (MAb)-based enzyme-linked immunosorbent assay (ELISA). Eight genome types were observed in the present study, among which D25, D26, D27, and D28 were novel genome types. These eight genome types were divided into two genome-type clusters (GTCs) based on phylogenetic analysis of the hypervariable regions (HVRs) of the hexon. GTC1 includes D1, D25, D26, D27, and D28, and the GTC2 contains D4, D12, and D22. The amino acid homologies among the members within a GTC were 97 to 100%, whereas between the members of different GTCs the homologies were 92 to 94%. The specificity of the GTC classification was confirmed by ELISA with MAb 1F, which was selected by the Ad41 prototype Tak strain. It was found that only the isolates of GTC1 but not of GTC2 reacted with MAb 1F. These results suggest that Ad41 isolates from the three countries should be classified into two subtypes. The accumulation of amino acid mutations located in HVRs of hexon are indicative for the classification of Ad41 subtype.

Development of a highly efficient purification process for recombinant adenoviral vectors for oral gene delivery

Recently, replication-deficient adenoviruses have received increasing attention as vector for gene delivery and as potential vaccine carriers. With the increased use of the vector in vivo and in clinical trails, the demand for a safe, rapid, and cost effective purification process has been heightened. In this report, a simple and efficient method for the purification of large quantities of live adenoviral vectors was developed. The process involved the replacement of cesium chloride (CsCl) gradients with sucrose gradients. Ultracentrifugation times were reduced and the desalting step eliminated, decreasing total preparation time by 15 hr. A 20-80% linear sucrose gradient provided optimal recovery of infectious viral particles and positioning of the viral band in the gradient. Purification with this gradient system produced a preparation containing 1.39 x 10(14) lac-forming units (lfu)/ml. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed that the process also removed all associated cellular proteins from the preparation. Studies have shown that direct lyophilization of the vector in sucrose after purification produces a product containing 1.4 x 10(12) lfu/ml. Minimal degradation was seen in the lyophilized preparation. A viral concentration of 6 x 10(11) lfu/ml was detected in the product after 150 days in storage at -20 degrees C. This approach will not only simplify the preparation of adenoviral vectors for in vivo studies and clinical trials, but will facilitate production of stable adenoviral formulations for oral gene delivery.

Genetic organization, size, and complete sequence of early region 3 genes of human adenovirus type 41

The complete nucleotide and predicted amino acid sequences for open reading frames (ORFs) of the human adenovirus type 41 (Ad41) early region 3 (E3) gene have been determined. The sequence of the Ad41 E3 gene (map units 74 to 83.9) consists of 3,373 nucleotides and has one TATA box and two polyadenylation signals (AATAAA). Analysis of the nucleotide sequence reveals that the E3 gene can encode six ORFs, designated RL1 to RL6. These are all expressed at the mRNA level, as determined by reverse transcription-PCR analysis of AD41-infected cell RNA. When compared with known E3 sequences of most other human adenoviruses deposited in GenBank, the sequences of RL1 to RL3 were found to be unique to subgroup F adenoviruses (Ad40 and Ad41). They encode putative proteins of 173 amino acids (19.4 kDa) and 276 amino acids (31.6 kDa) in one reading frame as well as a 59- amino-acid (6.7 kDa) protein in an overlapping reading frame. RL4 encodes a 90-amino-acid protein (10.1 kDa) with 40% homology to the Ad2 E3 10.4-kDa protein, which induces degradation of the epidermal growth factor receptor and functions together with the Ad2 E3 14.5-kDa protein to protect mouse cell lines against lysis. RL5 encodes a protein of 107 amino acid residues (12.3 kDa) and is analogous to the Ad E3 14.5-kDa protein. RL6 codes for a protein of 122 amino acids (14.7 kDa) that is analogous to the Ad2 14.7-kDa protein, which functions to protect Ad-infected cells from tumor necrosis factor-induced cytolysis. This finding of three unique (RL1 to RL3) E3 gene ORFs may explain why subgroup F adenoviruses differ substantially from other human adenoviruses in their host range; i.e., they replicate predominantly in the host's gastrointestinal rather than respiratory tract. A recent phylogenetic study that compared subgroup F Ad40 DNA sequences with representatives of subgroups B (Ad3), C (Ad2), and E (Ad4) reached a similar conclusion about the uniqueness of RL1 and RL2.

Human adenovirus type 41 contains two fibers

DNA sequencing of the subgroup F human adenovirus serotype 41 (TAK, Ad41) fiber gene revealed the presence of two adjacent open reading frames encoding information for proteins with molecular weights of 60.6 kDa and 41.4 kDa (Pieniazek, et al; Nucleic Acids Res. 18: p. 1901, 1990). In this paper, various approaches were used to characterize the two proteins and determine whether both fibers were expressed in infected cells as well as on viral particles. We initially used a reverse transcriptase-polymerase chain reaction with primers for the short and long fiber genes to amplify mRNA from Ad41 infected HEp-2 cells at 48 h post-infection. Two distinct DNA bands; one slightly larger than 1.1 kbp and the other at about 1.7 kbp were identified. Second, we used polyclonal anti-Ad41 virion and monoclonal anti-Ad5 fiber antibodies to demonstrate that at both 24 and 36 h post-infection, Ad41 expressed two fiber proteins of the expected size. Specifically, by SDS-PAGE, one fiber (short) had a molecular weight of 40 kDa, while the other (long) had a molecular weight of 60 kDa. Third, by electron microscopy, two sizes of fibers were released from CsCl purified virions, both having a characteristic adenovirus morphology, with a knob at one end. The long fiber measured 315A in length and the short fiber was 250A long. These measurements are consistent with the two Ad41 fibers being encoded by the above open reading frames. We also performed a computer search to compare fiber sequences from other human adenovirus serotypes with that of the Ad41 short and long fiber proteins. The primary structure of both Ad41 fibers were found to be similar in that they contained tail, shaft and knob regions. Further, the tail region of both fibers (amino acids 1-42) showed a 74% overall homology to each other and contained the Ad conserved sequence NH2-F-N-P-V-Y-P-Y-COOH. An interesting difference, however, was observed in the shaft region where the long fiber (amino acids 43-389) had twenty-two 16-amino acid repeat motifs, while the short fiber (amino acids 43-233) had only twelve. Finally, we noted that the long fiber knob region was about 15% longer than that of the short fiber, and showed little overall homology. In conclusion, human adenovirus subgroup F (type 41) virions appear to differ from those of all other human adenoviruses (subgenera A-E) in that they contain two fiber genes and correspondingly, two different sized fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenovirus type 40 and 41 growth in vitro: host range diversity reflected by differences in patterns of DNA replication

Subgroup F adenoviruses adapt poorly to cell culture, but the reasons for their fastidious nature are as yet ill defined. In an attempt to gain an overview of the differences in replication between adenovirus type 2 (Ad2) and representative strains of Ad40 and Ad41, cell lines which show different degrees of permissiveness to Ad40 and Ad41 were infected and examined with respect to three key functions in the Ad2 life cycle: host protein shutoff, DNA synthesis, and late antigen synthesis. The complexity of growth patterns exhibited by the subgroup F adenoviruses suggests that defectiveness is a multifactorial phenomenon not easily explainable by a single aberrant function. Furthermore, results suggest that there may be replicative defects in subgroup F adenoviruses which are not shared by both serotypes or by all strains.

A block in release of progeny virus and a high particle-to-infectious unit ratio contribute to poor growth of enteric adenovirus types 40 and 41 in cell culture

The fastidious enteric adenovirus (FEAd) types 40 (Ad40) and 41 (Ad41) are found in stool specimens of infants and young children in association with gastroenteritis. Although they can be isolated routinely from clinical specimens by using 293 cells, they are propagated with variable success in cell lines which support the replication of other adenovirus serotypes. HeLa cells are generally considered to be nonpermissive for the replication of FEAds, but in this study, Ad40 and Ad41 grew to comparable titers in individual 293 and HeLa cells. However, virus was not efficiently released from infected HeLa cells and thus did not undergo multiple cycles of infection in HeLa cell cultures. The block in virus release was not overcome in KB18 cells which, like 293 cells, constitutively express proteins encoded by the E1B region of a subgroup C adenovirus (in this case Ad2). Moreover, it was apparent from these studies that Ad40 and Ad41 have particle-to-infectious unit ratios several orders of magnitude greater than that for Ad5, even in 293 cells which express the E1A and E1B proteins of Ad5 and are considered to be permissive for replication of the FEAds. Neither the block in release of progeny virus nor the high particle-to-infectious unit ratio is explained solely by the defect in expression of the E1B 55K protein identified by Mautner et al. (V. Mautner, N. MacKay, and V. Steinthorsdottir, Virology 171:619-622, 1989; V. Mautner, N. MacKay, and K. Morris, Virology 179:129-138, 1990).

Growth of fastidious adenovirus serotype 40 in HRT 18 cells: interactions with E1A and E1B deletion mutants of subgenus C adenoviruses

Growth of fastidious adenovirus serotype 40 (Ad40) in several cell lines was investigated. Ad40 was able to readily propagate in human intestinal cell line, HRT 18. Coinfection assays were made in non-permissive and permissive cells between Ad40 and Ad5dl312 or dl1520, mutants deleted in E1A and E1B regions, respectively, to test the ability of Ad40 to complement these mutants and vice versa. Ad40 could enhance Ad5dl312 DNA synthesis in HRT18 and HeLa cells, although its own DNA disappeared in the presence of this mutant in HRT18 cells. In coinfection with dl1520, Ad40 DNA synthesis was inhibited by dl1520 in HRT18 cells and dl1520 DNA synthesis was inhibited by Ad40 in 293 cells. This might reflect the presence of unusual products encoded by Ad40 E1B region.

Human enteric adenovirus type 41 binding to HEp-2 cells is specific

Properties of human enteric adenovirus type 41 (Ad41) binding to its receptor on the surface of HEp-2 cells were investigated. The binding was found to be temperature-dependent, saturable, and specific. Analysis of the binding data showed a single class of 4.3 x 10(4) receptor sites per cell, an equilibrium dissociation constant of 21.0 nM, and no cooperativity among receptor sites. Trypsin-treated HEp-2 cells subsequently grown in the presence of tunicamycin or 2-deoxyglucose recovered full Ad41 binding activity, but could not if subsequently grown in the presence of cycloheximide. These data indicate that a single type of virus receptor, likely protein in nature, is present on the surface of HEp-2 cells to specifically bind Ad41.

Cellular transformation by E1 genes of enteric adenoviruses

The ability of Ad40 and Ad41 E1A plus E1B genes to transform BRK cells was considerably lower than that of Ad5 and Ad12 corresponding genes. However, as for Ad5, the E1A genes of enteric adenoviruses could cooperate with an activated ras oncogene for full cell transformation and the Ad41 E1B could be complemented by E1A gene of Ad5 or Ad12 for cell transformation. Complementation studies suggested that the conserved region 1 of Ad41 E1A was responsible for this inefficient transformation. The Ad40- and Ad41-transformed cell lines exhibited a low level of major histocompatibility complex (MHC) class I antigens correlated to the low level of Ad12-transformed cells. Class I MHC antigen amounts expressed at the surface of the cells transformed by the weakly oncogenic Ad3 were between the high level of Ad5- and the low level of Ad12-transformed cells.

Association of HSP70 with the adenovirus type 5 fiber protein in infected HEp-2 cells

Although maximal synthesis of HSP70 is induced early (6-12 hr) after adenovirus type 5 (Ad5) infection of HEp-2 or HeLa cells, the total amount of HSP70 appears to be increased at late times of infection (18-24 hr). Since virion structural proteins also accumulate at these times, we investigated the possible interaction between Ad5 structural proteins and HSP70 by immunoprecipitation of infected cell extracts with antibodies to either ATP-affinity-purified HSP70 or to CsCl-gradient-purified Ad5 virions. We found that HSP70 and a 62-kDa Ad-specific protein coimmunoprecipitated from infected cell extracts. Antibody which recognizes one of these two proteins does not cross-react with the other. Thus, the association between HSP70 and the 62-kDa protein appears specific. Using different antisera to specific adenovirus structural proteins, we have identified the 62-kDa protein as the Ad5 fiber protein.

Enteric adenovirus 41 (Tak) requires low serum for growth in human primary cells

It had been postulated that due to lack of growth of enteric adenovirus 41 (Ad41) on human primary cells and its growth on Graham-293 cells there was a defect in the Ad41 E1A region. However, we found as a result of careful evaluation of Ad41 growth on several primary cell lines (HEK, WI-38, or Detroit 551) that efficient viral multiplication is possible if the serum concentration in the medium used postinfection (p.i.) is kept between 0.2 and 1%. In contrast, only slight growth of Ad41 occurs in infected cells maintained in 5% serum and virtually no viral replication is found in infected cells cultivated in medium with 10% serum. The serum inhibitory effect appears limited to primary cells because no difference in Ad41 replication, as assayed by accumulation of Ad41 DNA, was found in infected continuous cell lines (HEp-2, 293) cultivated p.i. in either 1 or 10% FBS. Also, this effect appears specific for enteric adenoviruses, such as Ad41, since conventional adenoviruses, such as Ad5, grow well in both 1 and 10% FBS. The above results show that Ad41 can grow in a variety of primary cell lines, under specific culture conditions. In addition, we found that Ad41-infected primary cells grown in medium containing 0.2% serum had an increase in synthesis of the 70-kDa heat shock protein (HSP70) at about 6 hr p.i. and also Ad41 was able to complement the Ad5 E1A deletion mutant dl312. These results show that the E1A function of Ad41 is not impaired in infected cells.

Enteric adenoviruses

Human adenoviruses are classified into 47 serotypes and six subgenera (A-F) with different tropisms. In recent years adenovirus type 40 (Ad40) and 41 (Ad41) of subgenus F have been shown to be causative agents in enteric infections, which is second in importance only to rotaviruses as a cause of infantile gastroenteritis. Infection with EAds occurs worldwide and has been associated with 4-17% of cases of diarrhoea in children. AD40 and Ad41 primarily affect young children less than 2 years of age and occur throughout the year. The clinical characteristics include watery diarrhoea accompanied by vomiting, low grade fever and mild dehydration. A distinct feature of EAds infection is the protracted diarrhoea (mean 8.6 and 12.2 days for Ad40 and Ad41, respectively). Respiratory symptoms are infrequent. Serotypes Ad40 and Ad41 differ from all other (established) adenoviruses by being unable to replicate in conventional cell cultures. These fastidious viruses only grow in selected cell lines, 293 cells being the most commonly used. In spite of the difficulty of isolating Ad40 and Ad41, they can be directly identified and typed by ELISA and solid-phase immune electron microscopy. The amount of viral DNA in stool specimens is sufficient for identification by DNA restriction and dot-blot assays. The recent development of highly sensitive and specific monoclonal antibody-based ELISAs enable accurate diagnosis of adenovirus gastroenteritis in routine work and make possible the evaluation of the role of the enteric adenoviruses in diarrhoeal disease in the developing countries.