BALB/c mice infected with DENV-2 strain 66985 by the intravenous route display injury in the central nervous system.

Dengue is a mild flu-like arboviral illness caused by dengue virus (DENV) that occurs in tropical and subtropical countries. An increasing number of reports have been indicating that dengue is also associated to neurological manifestations, however, little is known regarding the neuropathogenesis of the disease. Here, using BALB/c mice intravenously infected with DENV-2 strain 66985, we demonstrated that the virus is capable of invading and damaging the host's central nervous system (CNS). Brain and cerebellum of infected animals revealed histological alterations such as the presence of inflammatory infiltrates, thickening of pia matter and disorganization of white matter. Additionally, it was also seen that infection lead to altered morphology of neuroglial cells and apoptotic cell death. Such observations highlighted possible alterations that DENV may promote in the host's CNS during a natural infection, hence, helping us to better understand the neuropathological component of the disease.

Dengue fatal cases present virus-specific HMGB1 response in peripheral organs.

Dengue is an important infectious disease that presents high incidence and yields a relevant number of fatal cases (about 20,000) every year worldwide. Despite its epidemiological relevance, there are many knowledge gaps concerning dengue pathogenesis, especially with regards to the circumstances that drive a mild clinical course to a severe disease. In this work, we investigated the participation of high mobility group box 1 (HMGB1), an important modulator of inflammation, in dengue fatal cases. Histopathological and ultrastructural analyses revealed that liver, lung and heart post-mortem samples were marked by tissue abnormalities, such as necrosis and apoptotic cell death. These observations go in line with an HMGB1-mediated response and raised concerns regarding the participation of this cytokine in promoting/perpetuating inflammation in severe dengue. Further experiments of immunohistochemistry (IHC) showed increased expression of cytoplasmic HMGB1 in dengue-extracted tissues when compared to non-dengue controls. Co-staining of DENV RNA and HMGB1 in the host cell cytoplasm, as found by in situ hybridization and IHC, confirmed the virus specific induction of the HMGB1-mediated response in these peripheral tissues. This report brings the first in-situ evidence of the participation of HMGB1 in severe dengue and highlights novel considerations in the development of dengue immunopathogenesis.

Peripheral Organs of Dengue Fatal Cases Present Strong Pro-Inflammatory Response with Participation of IFN-Gamma-, TNF-Alpha- and RANTES-Producing Cells.

Dengue disease is an acute viral illness caused by dengue virus (DENV) that can progress to hemorrhagic stages leading to about 20000 deaths every year worldwide. Despite many clinical investigations regarding dengue, the immunopathogenic process by which infected patients evolve to the severe forms is not fully understood. Apart from differences in virulence and the antibody cross reactivity that can potentially augment virus replication, imbalanced cellular immunity is also seen as a major concern in the establishment of severe dengue. In this context, the investigation of cellular immunity and its products in dengue fatal cases may provide valuable data to help revealing dengue immunopathogenesis. Here, based in four dengue fatal cases infected by the serotype 3 in Brazil, different peripheral organs (livers, lungs and kidneys) were studied to evaluate the presence of cell infiltrates and the patterns of local cytokine response. The overall scenario of the studied cases revealed a considerable systemic involvement of infection with mononuclear cells targeted to all of the evaluated organs, as measured by immunohistochemistry (IHC). Quantification of cytokine-expressing cells in peripheral tissues was also performed to characterize the ongoing inflammatory process by the severe stage of the disease. Increased levels of IFN-γ- and TNF-α-expressing cells in liver, lung and kidney samples of post-mortem subjects evidenced a strong pro-inflammatory induction in these tissues. The presence of increased RANTES-producing cell numbers in all analyzed organs suggested a possible link between the clinical status and altered vascular permeability. Co-staining of DENV RNA and IFN-γ or TNF-α using in situ hibridization and IHC confirmed the virus-specific trigger of the pro-inflammatory response. Taken together, this work provided additional evidences that corroborated with the traditional theories regarding the "cytokine storm" and the occurrence of uneven cellular immunity in response to DENV as major reasons for progress to severe disease.

The pathology of severe dengue in multiple organs of human fatal cases: histopathology, ultrastructure and virus replication.

Dengue is a public health problem, with several gaps in understanding its pathogenesis. Studies based on human fatal cases are extremely important and may clarify some of these gaps. In this work, we analyzed lesions in different organs of four dengue fatal cases, occurred in Brazil. Tissues were prepared for visualization in optical and electron microscopy, with damages quantification. As expected, we observed in all studied organ lesions characteristic of severe dengue, such as hemorrhage and edema, although other injuries were also detected. Cases presented necrotic areas in the liver and diffuse macro and microsteatosis, which were more accentuated in case 1, who also had obesity. The lung was the most affected organ, with hyaline membrane formation associated with mononuclear infiltrates in patients with pre-existing diseases such as diabetes and obesity (cases 1 and 2, respectively). These cases had also extensive acute tubular necrosis in the kidney. Infection induced destruction of cardiac fibers in most cases, with absence of nucleus and loss of striations, suggesting myocarditis. Spleens revealed significant destruction of the germinal centers and atrophy of lymphoid follicles, which may be associated to decrease of T cell number. Circulatory disturbs were reinforced by the presence of megakaryocytes in alveolar spaces, thrombus formation in glomerular capillaries and loss of endothelium in several tissues. Besides histopathological and ultrastructural observations, virus replication were investigated by detection of dengue antigens, especially the non-structural 3 protein (NS3), and confirmed by the presence of virus RNA negative strand (in situ hybridization), with second staining for identification of some cells. Results showed that dengue had broader tropism comparing to what was described before in literature, replicating in hepatocytes, type II pneumocytes and cardiac fibers, as well as in resident and circulating monocytes/macrophages and endothelial cells.