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.

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.

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.

Telomerase activity in thymomas and mammary gland adenocarcinomas induced by polyoma virus in AKR mice

Telomerase is an enzyme that stabilizes telomere lenght in transformed cells and tumors. Its role in tumor development is far from clear. In this paper, a new experimental model to study telomerase activity during tumorigenesis is presented. After infection with Polyoma virus, AKR mice developed thymomas and mammary gland adenocarcinomas. Polyoma antigens were observed by the peroxidase-antiperoxidase technique on tissue sections, and by Western blot on tumor extracts. The TRAP assay was performed to detect telomerase activity. It was not present in normal mammary gland, but it was positive in mammary gland adenocarcinomas. A different pattern was seen in thymic tissues: normal thymus had higher telomerase activity than thymomas. The incubation of thymoma extracts with normal thymus extracts decreased telomerase activity in the latter. These results demonstrate two different patterns of telomerase activity in tumors induced by Polyoma virus, and suggest the presence of telomerase inhibitory factors in thymomas.