Cytokines, adhesion molecules, and cellular infiltration in nephropathia epidemica kidneys: an immunohistochemical study.

Puumala hantavirus-induced nephropathia epidemica (NE) is an important cause for an acute reversible renal failure in Scandinavia, European Russia, and the Balkans. The characteristic histopathological renal finding is an acute tubulointerstitial nephritis. Mild to massive proteinuria, hematuria, and a rise in the serum creatinine level are typically seen. The pathogenetic mechanisms of NE kidney failure are incompletely understood. Therefore we studied the infiltrating cell populations and local expression of cytokines and growth factors in the kidney during the acute disease. Results of the histological and immunohistological studies of eight kidney biopsies show mild to moderate interstitial infiltration of lymphocytes, plasma cells, monocytes/macrophages, and polymorphonuclear leukocytes, mainly eosinophilic granulocytes and neutrophils. An increased expression of the cytokines tumor necrosis factor-alpha, transforming growth factor-beta, and platelet-derived growth factor was seen at the same sites mainly in the peritubular area of the distal nephron. Concomitantly also at the same locations expression of the endothelial adhesion molecules ICAM-1, VCAM, and PECAM was seen. Light microscopic changes in tubuli were common. Interestingly, despite the often massive transient proteinuria, no marked changes were seen in the glomeruli of NE kidneys. No evidence of Puumala virus was found in the kidney biopsies.

Effect of interferon-alpha and cell differentiation on Puumala virus infection in human monocyte/macrophages.

Pathogenesis of hantavirus infections is poorly understood. Puumala virus (PUU) is the etiologic agent of nephropathia epidemica, a form of hemorrhagic fever with renal syndrome common in Europe. We have studied PUU infection in primary human monocyte/macrophages and specifically the role of interferon alpha (IFN-alpha) and cell differentiation in it. PUU infection proceeded at a low level in monocyte/macrophages, and nucleocapsid (N) protein accumulation started 2 days postinfection. IFN-induced antiviral MxA protein was detected 3 days postinfection, suggesting IFN-alpha production in culture. IFN-alpha titers remained low, proposing that PUU is a poor IFN inducer. However, the PUU-induced IFN had an inhibitory effect on virus production as was shown by the effect of anti-IFN-alpha. Pretreatment of cells with IFN-alpha caused a dose-dependent inhibition of PUU N accumulation and reduced the yield of infectious virus. Monocytic U-937 cells overexpressing MxA protein were susceptible to PUU, suggesting that, unlike in some other negative strand RNA virus infections, MxA does not mediate resistance to PUU infection. Differentiation of monocyte/macrophages in culture and treatment of THP-1 promonocytic cells with phorbol 12-myristate 13-acetate made the cells more susceptible to PUU. The increased susceptibility of mature macrophages to PUU suggests that after differentiation to tissue macrophages they might function in the spread of the virus during PUU infection.

Susceptibility of human cells to Puumala virus infection.

Nephropathia epidemica involves several organs including kidney, lung, liver and brain. To investigate the susceptibility of putative target cells to the agent responsible, Puumala virus, we screened established human cell lines of lung (WI-38, A-427, CCD-11Lu), kidney (A-704), liver (Hep G2), pharynx (Detroit 562), submaxillary gland (A-253) and neural (SK-N-MC, SH-SY5Y) origin as well as primary human kidney glomerular cells, endothelial cells and peripheral blood monocytes/macrophages. Propagation of the Sotkamo strain of Puumala virus was also tested in the primary kidney, spleen and lung cells of bank voles (the natural host of the virus). All of the primary cells and most of the established cell lines expressed viral protein, synthesized viral RNA and secreted infectious virus, except the neural SK-N-MC and SH-SY5Y cells. None of the tested cell types except the primary bank vole kidney cells could propagate the virus as efficiently as the Vero E6 cells. The observed host cell range is wide and consistent with a multiorgan involvement of Puumala virus. No cytopathic effects were seen in any of the infected cell cultures.

Anti-endothelial cell antibodies in nephropathia epidemica and other viral diseases.

Increased capillary permeability is a central feature of the severe forms of haemorrhagic fever with renal syndrome (HFRS) and occurs also, though less frequently, in nephropathia epidemica (NE), one of the milder forms of this syndrome, caused by Puumala virus. We therefore searched for antiendothelial cell antibodies (AECA) in patients with NE and in those with other presumed or serologically proven acute viral illnesses. By enzyme immunoassay, using human umbilical vein endothelial cells (HUVEC) as the substrate, IgG class AECA were detected significantly more frequently in patients with NE and with influenza A than in Red Cross blood donors. A lesser degree of reactivity could be shown with a human alveolar cell carcinoma line and with human and mouse embryonic fibroblasts. Pretreatment of HUVEC with interferon-gamma (IFN-gamma), but not with IL-1 or tumour necrosis factor-alpha (TNF-alpha), increased their ability to bind IgG of sera from patients with NE and acute febrile illnesses. We conclude that, although AECA can be demonstrated in NE, they occur also in other acute viral illnesses and, unless cytopathic by a mechanism not shared by the AECA of these other illnesses, are unlikely to be casually related to the capillary leak in HFRS.