Key words: dengue-2 virus -BALB/c mice -C6/36 cell line -macrophage -mast cell -ultrastructure Dengue fever (DF) is an acute infectious disease caused by dengue virus (DENV) (Halstead 1988, Henchal & Putnak 1990) that belong to the Flavivirus genus of the Flaviviridae family of single-stranded, positive-polarity, enveloped RNAviruses (Chambers et al. 1990). Dengue disease (DEN) has a spectrum of clinical signs and symptoms, ranging from asymptomatic infection to severe and lethal manifestations. The four DENV serotypes (DENV-1, -2, -3, -4) may cause dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) in humans, with an estimated 100 million new cases of DF and over 250,000 cases of DHF/DSS per year worldwide. The major difficulty in studying DENV infection in humans and for developing a vaccine, is the absence of a suitable animal model which develops a disease with similar aspects of the DHF and DSS (Bhamarapravati 1993). Several studies suggest that mice are a permissive host for DENV (Meiklejhon et al. 1952, Lin et al.1998, Johnson & Roehrig 1999), but in the majority of these models the animals are im- (Table). In the present study we characterized the injuries caused by DENV-2 infection in lung tissue of BALB/c mice using photonic and electron transmission microscopies. Differing from the majority of the mice models, the DENV-2 (nonneuroadapted) were obtained from a patient serum, propagated once in the C6/36 cell line and inoculated by intravenous (i.v.) and intraperitoneal (i.p.) routes.
MATERIALS AND METHODS
Virus -The virus strain used in our experiments was isolated from a patient serum during an epidemic of DENV-2 in the state of Rio de Janeiro in 1995 and propagated in the Aedes albopictus mosquito cell line (C6/ 36). The serum was tested by the indirect immunofluorescence technique using a type specific DENV-2 monoclonal (3H5, DENV-2) antibody. The virus had not undergone passage in mouse brain. The titer of the virus (10 6.3 TCID 50 /0.1 ml) was calculated by the method of Reed and Muench (1938).Cells -The C6/36 monolayers were grown in L-15 medium supplemented with 1% non-essencial aminoacids, 10% tryptose phosphate broth, and 10% fetal bovine serum. The tubes were kept at 28 o C.Animal -Adult male BALB/c mice, aged 2 months and weighing 25 g, were obtained from the mouse colony maintained in the Department of Virology of the Instituto Oswaldo Cruz-Fiocruz. Mice were i.p. and i.v. inoculated with DENV-2 (dose of 10,000 TCID 50 /0.2 ml) and sacrificed after 48, 72 h, 7 and 49 days p.i. Non-infected mice and mice inoculated with L-15 medium were used as controls and sacrificed at the same time. The experiments were previously approved by the Animal Experimentation Ethical Committee of the Instituto Oswaldo Cruz-Fiocruz.Processing of tissues for photonic microscopy analysis -The animals were peritoneally anaesthetized and lung tissue fragments were collected from infected and non-infected mice. Samples were fixed in Millonig's fixative, dehydrated in ethanol, and paraffin-embedded. Sections (5...