Striated muscle involvement in experimental oral infection by herpes simplex virus type 1.

Herpes simplex virus type 1 is one of the most frequent causes of oral infection in humans, especially during early childhood. Several experimental models have been developed to study the pathogenesis of this virus but all of them employed adult animals. In this work, we developed an experimental model that uses mice younger than 4 days old, to more closely resemble human infection. Mice were infected subcutaneously with the prototype strain McIntyre of Herpes simplex-1, and the progression of infection was studied by immunoperoxidase. All animals died within 24-72 h post-infection, while viral antigens were found in the oral epithelium, nerves and brain. The most striking result was the finding of viral antigens in the nucleus and cytoplasm of cells belonging to striated muscles. Organotypic cultures of striated muscles were performed, and viral replication was observed in them by immunocytochemistry, electron microscopy and viral isolation. We conclude that the infection of striated muscles is present from the onset of oral infection and, eventually, could explain some clinical observations in humans.

Detection of polyomavirus major capsid antigen (VP-1) in human pilomatricomas.

The family Polyomaviridae is composed of small, non-enveloped, double-stranded DNA viruses widely used to study cell transformation in vitro and tumor induction in vivo. The development of pilomatricomas in mice experimentally infected with polyomavirus led us to detect the viral major capsid protein VP-1 in human pilomatricomas. This tumor, even uncommon, is one of the most frequent benign hair follicle tumors in humans and is composed of proliferating matrix cells that undergo keratinization, and form cystic neoplasms. The detection of VP-1 was performed using the peroxidase-antiperoxidase technique in paraffin-embedded slides with a specific primary serum. Adjacent slides treated with normal rabbit serum as a primary were employed as internal control. Positive and negative controls were also employed as well as slides of lesions caused by human papillomavirus to rule out any unspecific cross-reactivity. In 4 out of 10 cases polyomavirus VP-1 was clearly detected in nuclei of human pilomatricomas proliferating cells, in a patchy pattern of distribution. The controls confirmed the specificity of the immunocytochemical procedure. These results could indicate either an eventual infection of the virus in already developed tumors or alternatively, a direct involvement of polyomavirus in the pathogenesis of some pilomatricomas. The recent discovery of a new human polyomavirus associated with Merkel cell carcinomas has been a strong contribution to better understand the pathogenesis of some human uncommon skin cancers. Hopefully the results reported in this work will encourage further research on the role of polyomavirus in other human skin neoplasms.

In Vitro infection of human dura-mater fibroblasts with Staphylococcus aureus: colonization and reactive production of IL-1beta.

OBJECTIVE: Post-operative meningitis, caused mainly by Staphylococcus aureus and Gram-negative rods, is a life-threatening complication after neurosurgery, and its pathogenesis is far from clear. The purpose of this work was to study the experimental infection of human dura-mater fibroblasts and whole human dura by S. aureus. METHODS: In vitro cultures of human dura-mater fibroblasts and organotypic cultures of small pieces of human dura mater were inoculated with a human-derived S. aureus strain. The pattern of bacterial infection as well as cytokines secretion by the infected fibroblasts was studied. RESULTS: Our results suggest that colonisation of human dura-mater fibroblasts in culture and whole dura-mater tissue by S. aureus includes bacterial growth on the cell surface, fibroblast intracellular invasion by bacteria and a significant synthesis of interleukin 1beta (IL-1beta) by the infected cells. CONCLUSION: This is the first report of human dura-mater fibroblast infection by S. aureus. Hopefully, these results can lead to a better understanding of the pathogenesis of meningitis caused by this bacterial species and to a more rational therapeutic approach.

[The paradox of polyomaviruses. Lytic infection or tumor induction?]. / La dicotomía de los virus polioma. Infección lítica o inducción de neoplasias?

Murine polyomaviruses can produce lytic infections in mouse cell cultures or transform in vitro rat fibroblasts through a complex interaction with key cellular regulators. After infection of newborn mice, some strains of polyomavirus induce epithelial and mesenchymal tumors. It has been described that there is a direct relationship between viral dissemination in the mouse and tumor induction. However, at a single cell level lytic infection and transformation would not be able to coexist. The existence of 3 distinct cell populations in polyoma-induced tumors, classified according to the presence or absence of viral DNA and viral capsid protein VP-1 have been described. We have reported a fourth type of cell in the neoplasms, that can express the early and the late viral genes but do not allow virus assembly, probably due to underphosphorylation of VP-1. The mechanisms of polyoma intracellular migration and dissemination in the mouse are discussed, related to the virus' ability of tumor induction.

An antiviral principle present in a purified fraction from Melia azedarach L. leaf aqueous extract restrains herpes simplex virus type 1 propagation.

Meliacine (MA), an antiviral principle isolated from leaves of Melia azedarach L., exhibits potent antiviral activity against herpes simplex virus type 1 (HSV-1) by inhibiting specific infected-cell polypeptides (ICPs) produced late in infection. Some of these are involved in DNA synthesis and in the assembly of nucleocapsids. The present report provides additional evidence to elucidate the mode of action of MA against HSV-1. Time-of-addition experiments confirmed that MA affects a late event in the multiplication cycle of HSV-1. We showed that MA diminished the synthesis of viral DNA and inhibited the spread of infectious viral particles when HSV-1 that expresses beta-galactosidase activity was used. In addition, the lack of a protein with an apparent MW of 55 KD was detected in MA-treated cell extracts. Ultrastructural analysis of infected cells showed that, in the case of MA treatment, a large number of unenveloped nucleocapsids accumulated in the cytoplasm and a minor proportion of mature virus was found in cytoplasmic vesicles.These findings suggest that MA exerts an antiviral action on both the synthesis of viral DNA and the maturation and egress of HSV-1 during the infection of Vero cells.

La dicotomia de los virus polioma: infeccion litica o induccion de neoplasias? / The paradox of polyomaviruses: lytic infection or tumor induction?

Los virus Polioma murinos provocan infecciones líticas en cultivos de células de ratón y transforman in vitro células de rata a través de la interacción de su oncogén mT con diversos reguladores celulares. Luego de su inoculación en ratones neonatos inducen neoplasias epiteliales y mesenquimáticas. Se ha propuestoque las cepas de polioma más oncogénicas son aquellas que previamente replican más en el ratón. Sin embargo, a nivel de una sola célula la infección lítica y la transformación deberían ser mutuamente excluyentes.En cada neoplasia han sido descriptos 3 tipos celulares según expresen el DNA viral solo o concomitantementecon la proteína mayor de la cápside VP1, o que no contengan DNA viral ni VP-1. En nuestro laboratorio detectamos la existencia de un cuarto tipo celular en las neoplasias, en el que se expresa la totalidad del genoma viral pero no ocurre el ensamblaje, probablemente por alteraciones en la fosforilación de VP-1. Se discuten los mecanismos de migración intracelular de Polioma, la diseminación en el ratón y los factores que podrían estarinvolucrados en la inducción de neoplasias o en la infección lítica inducidas por el virus.

Progression of intravaginal infection by herpes simplex-2 in genetically athymic mice

The purpose of this paper was to study the pathogenesis of wild-type Herpes simplex-2 (HSV-2) primary intravaginal (IVAG) infection in genetically athymic (nude) mice. Nude (nu/nu) N: NIH(S) and Balb/c mice, as well as their euthymic counterparts were IVAG infected with 5 x 10(5) pfu of HSV-2. The progression of the infection was followed by HSV-2 immunolabeling using the peroxidase-antiperoxidase technique in tissue sections of the whole body, electron microscopy, and viremia titration at two different timepoints. 70 per cent of athymic NIH mice, 30 per cent of euthymic NIH mice, and 80 per cent of both athymic and euthymic Balb/c mice developed acute vulvovaginitis and died between 8-10 days post-infection (pi). Viremia was not detected in either athymic or euthymic mice. HSV-2 replicated in the vulvovaginal, vesical and perianal epithelia, then progressed towards the central nervous system mainly along autonomic nerves and ganglia. HSV-2 antigens were not detected in liver, spleen, kidney, skin, heart, lung or bone marrow. The conclusion is that the T-cell immune response seems to limit the IVAG infection of NIH mice at the inoculation site, but is not involved in preventing HSV-2 dissemination through the blood.

Immunocytochemical and morphological effects of short-term stimulation of cultured astrocytes

Both image analysis at light microscopy level and ultrastructural characterization by transmission electron microscopy were employed to evaluate the differentiation stage in young cultured mouse astrocytes after 1-day exposure to dBcAMP, a chemical compound known to induce cell activation. The aim was to validate an experimental model of stimuled astrocytes preserving the properties of recently seeded cells, thus avoiding the overlapping effects of in vitro aging. Differentiated astrocytes, as evidenced by GFAP labeling by streptavidin-perioxidase, doubled their number in treated cultures (45 per cent) versus controls (23 per cent). In addition, a significant increase in processing-bearing astrocytes (elongated forms) to the detriment of immature polygonal astrocytes, was recorded. No noticeable changes were found in cell perimeter, but cell area displayed a significant reduction in labeled surface of astrocytes undergoing morphological differentiation. Concomitantly, electron microscopy showed that radially organized bundles of numerous intermediate filaments compatible with GFAP replaced the few scattered structures observed in control cultures. However methodological caution is advisable as regards the relevance of the in vitro counterpart in situ reactive astrocytes, since cell plasicity is recognized to depend on culture conditions. At any rate, present quantitative results demonstrate that GFAP-positive cell percentage and cell area measurement are adequate parameters of early immunocytochemical and morphological differentiation, respectively, and thus contribute to a better histometric characterization of an easily available substrate to discriminate the wide variety of factors involved in CNS response to injury.