The comparative pathology of severe acute respiratory syndrome and avian influenza A subtype H5N1--a review

The pathology of 2 zoonotic human viral infections that recently emerged, severe acute respiratory syndrome (SARS) due to coronavirus (SARS-CoV) and avian influenza A subtype H5N1, is reviewed and compared based on the literature and the cases examined by the authors. Pneumocytes are the primary target of infection resulting in diffuse alveolar damage. Systemic cytokine activation results in hemophagocytic syndrome, lymphoid depletion, and skeletal muscle fiber necrosis. Severe acute respiratory syndrome induces a more fibrocellular intra-alveolar organization with a “bronchiolitis obliterans organizing pneumonia”–like pattern and presence of multinucleated histiocytes and pneumocytes. H5N1 causes a more fulminant and necrotizing diffuse alveolar damage with patchy and interstitial paucicellular fibrosis. Severe acute respiratory syndrome associated coronavirus persists in the lung up to the second month, whereas H5N1 persists in the lung up to the third week. Severe acute respiratory syndrome associated coronavirus disseminates to blood, urine, feces, gastrointestinal tract, and liver. There is recent report of possible cerebral involvement by H5N1 and its isolation in the blood, gastrointestinal tract, and cerebrospinal fluid. More pathologic studies are urgently needed.

Modeling the early events of severe acute respiratory syndrome coronavirus infection in vitro

The clinical picture of severe acute respiratory syndrome (SARS) is characterized by pulmonary inflammation and respiratory failure, resembling that of acute respiratory distress syndrome. However, the events that lead to the recruitment of leukocytes are poorly understood. To study the cellular response in the acute phase of SARS coronavirus (SARS-CoV)-host cell interaction, we investigated the induction of chemokines, adhesion molecules, and DC-SIGN (dendritic cell-specific ICAM-3-grabbing nonintegrin) by SARS-CoV. Immunohistochemistry revealed neutrophil, macrophage, and CD8 T-cell infiltration in the lung autopsy of a SARS patient who died during the acute phase of illness. Additionally, pneumocytes and macrophages in the patient's lung expressed P-selectin and DC-SIGN. In in vitro study, we showed that the A549 and THP-1 cell lines were susceptible to SARS-CoV. A549 cells produced CCL2/monocyte chemoattractant protein 1 (MCP-1) and CXCL8/interleukin-8 (IL-8) after interaction with SARS-CoV and expressed P-selectin and VCAM-1. Moreover, SARS-CoV induced THP-1 cells to express CCL2/MCP-1, CXCL8/IL-8, CCL3/MIP-1alpha, CXCL10/IP-10, CCL4/MIP-1beta, and CCL5/RANTES, which attracted neutrophils, monocytes, and activated T cells in a chemotaxis assay. We also demonstrated that DC-SIGN was inducible in THP-1 as well as A549 cells after SARS-CoV infection. Our in vitro experiments modeling infection in humans together with the study of a lung biopsy of a patient who died during the early phase of infection demonstrated that SARS-CoV, through a dynamic interaction with lung epithelial cells and monocytic cells, creates an environment conducive for immune cell migration and accumulation that eventually leads to lung injury.

How the SARS coronavirus causes disease: host or organism?

The previous epidemic of severe acute respiratory syndrome (SARS) has ended. However, many questions concerning how the aetiological agent, the novel SARS coronavirus (CoV), causes illness in humans remain unanswered. The pathology of fatal cases of SARS is dominated by diffuse alveolar damage. Specific histological changes are not detected in other organs. These contrast remarkably with the clinical picture, in which there are apparent manifestations in multiple organs. Both pathogen and host factors are important in the pathogenesis of SARS. The choice of specific receptors and the unique genome of the SARS‐CoV are important elements in understanding the biology of the pathogen. For the host cells, the outcome of SARS‐CoV infection, whether there are cytopathic effects or not, depends on the cell types that are infected. At the whole‐body level, immune‐mediated damage, due to activation of cytokines and/or chemokines and, perhaps, autoimmunity, may play key roles in the clinical and pathological features of SARS. Continued research is still required to determine the pathogenetic mechanisms involved and to combat this new emerging human infectious disease. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Severe acute respiratory syndrome coronavirus infection of human ciliated airway epithelia: role of ciliated cells in viral spread in the conducting airways of the lungs

Severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in 2002 as an important cause of severe lower respiratory tract infection in humans, and in vitro models of the lung are needed to elucidate cellular targets and the consequences of viral infection. The SARS-CoV receptor, human angiotensin 1-converting enzyme 2 (hACE2), was detected in ciliated airway epithelial cells of human airway tissues derived from nasal or tracheobronchial regions, suggesting that SARS-CoV may infect the proximal airways. To assess infectivity in an in vitro model of human ciliated airway epithelia (HAE) derived from nasal and tracheobronchial airway regions, we generated recombinant SARS-CoV by deletion of open reading frame 7a/7b (ORF7a/7b) and insertion of the green fluorescent protein (GFP), resulting in SARS-CoV GFP. SARS-CoV GFP replicated to titers similar to those of wild-type viruses in cell lines. SARS-CoV specifically infected HAE via the apical surface and replicated to titers of 10(7) PFU/ml by 48 h postinfection. Polyclonal antisera directed against hACE2 blocked virus infection and replication, suggesting that hACE2 is the primary receptor for SARS-CoV infection of HAE. SARS-CoV structural proteins and virions localized to ciliated epithelial cells. Infection was highly cytolytic, as infected ciliated cells were necrotic and shed over time onto the luminal surface of the epithelium. SARS-CoV GFP also replicated to a lesser extent in ciliated cell cultures derived from hamster or rhesus monkey airways. Efficient SARS-CoV infection of ciliated cells in HAE provides a useful in vitro model of human lung origin to study characteristics of SARS-CoV replication and pathogenesis.

[Investigation of proximal femoral marrow with magnetic resonance imaging in recovered patients with severe acute respiratory syndrome]

OBJECTIVE

To determine the effect of corticosteroid treatment and severe acute respiratory syndrome (SARS) infection itself on the marrow conversion in the proximal femoral marrow in the recovered patients of health care workers with SARS.

METHODS

The distribution of proximal femoral marrow on MR imaging of 148 health care workers with recovered SARS including 106 cases treated with varied dosage of steroids and 42 cases without steroid, and 97 age and sex matched health adults as controls were observed. The index of marrow conversion (signal intensity of the femoral neck and intertrochanteric area divided by signal intensity of the greater trochanter multiplied by 100%) was quantitatively measured and compared between SARS patients treated with steroid and without steroid and the normal control group.

RESULTS

In 106 cases treated with steroid of the 148 health care workers, femoral head osteonecrosis was found in 4 cases, bilateral femoral marrow edema in 2 cases, femoral marrow infarction in 1 case. The index of marrow conversion in the normal controls, in SARS patients treated without and with steroids was (79.4 +/- 6.8)%, (86.9 +/- 7.4)%, (88.6 +/- 5.9)%, respectively. There was significantly statistical difference between groups (P < 0.05).

CONCLUSION

In addition to fat conversion in the proximal femoral marrow due to steroid treatment, the infection of SARS itself may promote an excessively conversion of the red marrow to yellow marrow of the femoral neck in SARS patients.

[Expression and significance of severe acute respiratory syndrome associated coronavirus (SARS-CoV)-X4 protein in lungs of SARS patients]

OBJECTIVE

To investigate the significance of severe acute respiratory syndrome associated coronavirus (SARS-CoV)-X4 protein expression in lungs of patients with SARS.

METHODS

Pathological features of the lungs from 4 SARS patients were examined and the expression of SARS-CoV-X4 protein in the lungs was evaluated with immunohistochemical staining using specific antibodies against protein X4.

RESULTS

Microscopically, all lungs from 4 cases showed edema, erythrocyte and fibrin exudates in the alveoli, hyperplasia of alveolar epithelium, necrosis, hyaline membrane formation and fibroblast foci. Immunohistochemical stains showed a strong positivity of X4 protein in denudation cells, vascular endothelial cells and also erythrocytes and neutrophils in the alveoli of the lung tissues from the 4 cases.

CONCLUSIONS

Expression of SARS-CoV-X4 protein in the lungs may be involved in the pathogenesis and progression of SARS.

Clinical and laboratory features in the early stage of severe acute respiratory syndrome

BACKGROUND AND PURPOSE

To characterize the clinical and laboratory features of severe acute respiratory syndrome (SARS) in the early stage and to compare them with those of patients initially suspected of having SARS who were later determined to have other febrile diseases.

METHODS

Between March and June 2003, 122 patients with possible SARS were admitted to the isolation ward of Tri-Service General Hospital. SARS was diagnosed according to the modified World Health Organization case definition (May 1, 2003). Among them, 43 were classified as probable SARS cases and a SARS etiology was excluded in 32 patients.

RESULTS

Presenting symptoms on admission included fever (97.7% of probable cases, 84.4% of excluded cases), chills (39.5% vs 18.8%), cough with sputum production (16.3% vs 40.6%), dry cough (23.3% vs 9.4%), dyspnea (18.6% vs 9.4%), diarrhea (14.0% vs none), rhinorrhea (2.3% vs none), and myalgia (7.0% vs 6.6%). Common laboratory features included lymphopenia and elevated aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, C-reactive protein and creatine kinase values. Intubation and mechanical ventilation were required in 12 probable cases and 6 excluded cases. Five patients with probable SARS (11.6%) died. A scoring system which was developed to differentiate SARS patients from other febrile patients in the emergency room could differentiate probable cases from excluded cases with a sensitivity of 36.4% and a specificity of 70.6%.

CONCLUSIONS

The clinical presentation and laboratory features at the early stage do not allow differentiation of patients with SARS-CoV infection from other febrile patients. Thus, it is mandatory for all healthcare workers to strictly follow standard isolation precautions during an outbreak to minimize disease transmission.

The clinical presentation and outcomes of children infected with newly identified respiratory tract viruses

Numerous emerging respiratory tract viruses have been identified as significant causes of acute upper and lower respiratory tract illness in children. Human metapneumovirus is a paramyxovirus discovered in 2001 in the Netherlands, with a seasonal occurrence and spectrum of clinical illness most similar to the closely related respiratory syncytial virus. Several new members of the corona-virus family have been identified, including the truly novel agent of severe acute respiratory syndrome and others that probably have been circulating undetected. Avian influenza strains have caused numerous outbreaks with high mortality, including children, and are potential causes of pandemic influenza. Several zoonotic paramyxoviruses, including Nipah and Hendra viruses, have emerged as occasional causes of sever outbreaks of respiratory tract illness in children and adults.

ACE2 receptor expression and severe acute respiratory syndrome coronavirus infection depend on differentiation of human airway epithelia

Studies of patients with severe acute respiratory syndrome (SARS) demonstrate that the respiratory tract is a major site of SARS-coronavirus (CoV) infection and disease morbidity. We studied host-pathogen interactions using native lung tissue and a model of well-differentiated cultures of primary human airway epithelia. Angiotensin converting enzyme 2 (ACE2), the receptor for both the SARS-CoV and the related human respiratory coronavirus NL63, was expressed in human airway epithelia as well as lung parenchyma. As assessed by immunofluorescence staining and membrane biotinylation, ACE2 protein was more abundantly expressed on the apical than the basolateral surface of polarized airway epithelia. Interestingly, ACE2 expression positively correlated with the differentiation state of epithelia. Undifferentiated cells expressing little ACE2 were poorly infected with SARS-CoV, while well-differentiated cells expressing more ACE2 were readily infected. Expression of ACE2 in poorly differentiated epithelia facilitated SARS spike (S) protein-pseudotyped virus entry. Consistent with the expression pattern of ACE2, the entry of SARS-CoV or a lentivirus pseudotyped with SARS-CoV S protein in differentiated epithelia was more efficient when applied to the apical surface. Furthermore, SARS-CoV replicated in polarized epithelia and preferentially exited via the apical surface. The results indicate that infection of human airway epithelia by SARS coronavirus correlates with the state of cell differentiation and ACE2 expression and localization. These findings have implications for understanding disease pathogenesis associated with SARS-CoV and NL63 infections.

Pathogenesis of avian flu H5N1 and SARS

Avian influenza A (H5N1) and severe acute respiratory syndrome (SARS) coronavirus are infections that cause a severe viral pneumonia leading to acute respiratory dysfunction syndrome and carry a high case-fatality rate. We have investigated innate immune responses to both viruses using primary human macrophages and respiratory epithelial cells as in vitro models. In contrast to human influenza A H1NI viruses, the H5N1 viruses hyper-induce cytokines (tumour necrosis factor [TNF]alpha, interferon beta) and chemokines (IP10, MIP1alpha, MCP) in in vitro cultures of primary human macrophages. A similar differential effect is observed in primary human bronchial epithelial cells and in type 2 pneumocytes although TNFalpha is not induced in respiratory epithelial cells. The cell signalling pathways responsible for this differential effect remain to be explored. Preliminary data suggest that such differential signalling involves p38 MAP kinase rather than NF-kappaB. SARS coronavirus infection of primary human macrophages is associated with a strong induction of chemokines without an associated type 1 interferon response. These observations may be relevant in disease pathogenesis.

Acute respiratory distress syndrome in a child with human parvovirus B19 infection

A 6-year-old girl developed shock and multiple organ dysfunction including acute respiratory distress syndrome in association with parvovirus B19 infection. The diagnosis was based on positive antibodies and the detection of parvovirus 19 DNA in serum, bronchial secretions and skin biopsy. It seems likely, but it was not proved, that the parvovirus infection caused acute respiratory distress syndrome.

[Expression of SARS-CoV in various types of cells in lung tissues]

OBJECTIVE

To investigate the cell types infected by severe acute respiratory syndrome-associated coronavirus (SARS-CoV) in lung tissues and explore the mechanism of lung injury in SARS.

METHODS

In-situ hybridization(ISH) and immunohistochemistry(IHC) double staining was applied to study the lung tissues from 7 SARS cases of Beijing and one of Anhui province. According to SARS-CoV genome sequence, the cDNA probe was synthesized and labelled by digoxin. Immunohistochemically, antibodies of cytokeratin(CK), CD34, CD68, Vimentin and CD3 were applied to demonstrate bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, fibroblasts and T cells respectively.

RESULTS

The positive results of in-situ hybridization showed that the lung tissues of all cases expressed SARS-CoV RNA, and positive signals displayed in cytoplasms (purple-blue, NBP-BCIP. ISH-IHC double staining showed that positive signals of both ISH (purple-blue NBT-BCIP and IHC (red-brown, AEC expressed in the cytoplasms (purple and red). The positive results of double staining indicated that bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, fibroblasts and T lymphocytes were diffusely infected by SARS-CoV.

CONCLUSION

This study of ISH-IHC double staining in lung tissues of SARS patients showed that bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, T lymphocytes and fibroblasts were attacked diffusely in SARS lungs. Various types of cells damaged by SARS-CoV and inflammatory mediators released by those cells play an important role in the pathogenesis of lung injury in SARS.

[Lung pathology and pathogenesis of severe acute respiratory syndrome: a report of six full autopsies]

OBJECTIVE

Severe acute respiratory syndrome (SARS) is an emerging infectious disease that first manifested in humans in November 2002. The SARS-associated coronavirus (SARS-CoV) has been identified as the causal agent, but the pathology and pathogenesis are still not quite clear.

METHODS

Post-mortem lung samples from six patients who died from SARS from April to July 2003 were studied by light and electron microscopy, Masson trichromal staining and immunohistochemistry. Evidence of infection with the SARS-CoV was determined by reverse-transcription PCR (RT-PCR) , serological examination and electron microscopy.

RESULTS

Four of six patients had serological and RT-PCR evidence of recent infection of SARS-CoV. Morphologic changes are summarized as follows: (1) Diffuse and bilateral lung consolidation was seen in all patients (6/6) with increasing lung weight. (2) Diffuse alveolar damage was universal (6/6) with hyaline membrane formation (6/6), intra-alveolar edema/hemorrhage (6/6), fibrin deposition (6/6), pneumocyte desquamation (6/6). A marked disruption in the integrity of the alveolar epithelium was confirmed by immunostaining for the epithelial marker AE1/AE3 (6/6). (3) Type II pneumocytes, with mild hyperplasia, atypia, cytomegaly with granular amphophilic cytoplasm and intracytoplasmic lipid accumulation (5/6). (4) Giant cells in the alveoli were seen in five of 6 patients (5/6) , most of which were positive for the epithelial marker AE1/AE3 (5/6), but some cells were positive for the macrophage marker CD68(2/6). (5) A pronounced increase of macrophages were seen in the alveoli and the interstitium of the lung (6/6), which was confirmed by histological study and immunohistochemistry. (6) Haemophagocytosis was present in five of the 6 patients(5/6). (7) Lung fibrosis was seen in five patients(5/6), with alveolar septa and interstitium thickening(5/6), intraalveolar organizing exudates (6/6) and pleura thickening (4/6). Proliferation of collagen was confirmed by Masson trichromal staining, most of which was type III collagen by immunostaining. The formation of distinctive fibroblast/myofibroblast foci was seen in five patients (5/6) by light microscopy and immunochemistry. (8) Squamous metaplasia of bronchial mucosa was seen in five patients(5/6). (9) Thrombi was seen in all patients(6/6). (10) Accompanying infection was present in two patients, one was bacteria, the other was fungus. In addition, electron microscopy revealed viral particles in the cytoplasm of alveolar epithelial cells and endothelial cells corresponding to coronavirus.

CONCLUSION

Direct injury of SARS-CoV on alveolar epithelium, prominent macrophage infiltration and distinctive fibroblast/myofibroblast proliferation may play major roles in the pathogenesis of SARS.

Pathology of guinea pigs experimentally infected with a novel reovirus and coronavirus isolated from SARS patients

Guinea pigs were inoculated with a reovirus (ReoV) and coronavirus (SARS-CoV) isolated from SARS patients to determine their potential role in the etiology of SARS. Animals infected with ReoV died between day 22 and day 30 postinoculation (PI) while 70% of the animals inoculated with ReoV and SARS-CoV died between day 4 to day 7 PI. The titer of neutralizing antibodies against ReoV and SARS-CoV ranged from 80 to 160 when the animals were inoculated with the two viruses, respectively, while the titer of the antibodies was just below 10 in coinfections. The animal inoculated with ReoV developed diffuse alveolar damage similar to the exudative and leakage inflammation found in SARS patients, and was characterized by diffuse hemorrhage, fibroid exudation, hyaline membrane formation, and type II pneumocytes hyperplasia in alveolar interstitia. The pulmonary epithelial necrosis, excoriation, and early fibrosis of pulmonary tissue were only observed in ReoV-SARS-CoV groups and in SARS-CoV/ReoV groups. Other typical pathological changes included hemorrhagic necrosis in lymph nodes and spleen and hydropic degeneration in the liver. On the contrary, guinea pigs infected with SARS-CoV only developed interstitial pneumonitis. Our experiment demonstrate that ReoV might be one of the primary causes of SARS, since simultaneous coinfection can duplicate the typical pathological changes similar to that of SARS patients. This guinea pig model may provide a useful animal model for SARS.

Experimental infection of macaques with the human reovirus BYD1 strain: an animal model for the study of the severe acute respiratory syndrome

Experimental studies were performed to determine the role of a newly isolated reovirus (ReoV) from a severe acute respiratory syndrome (SARS) patient in the etiology of this newly described serious respiratory syndrome. Four cynomologus macaques were inoculated with this reovirus (BYD1) in an attempt to replicate the infection and pathology observed in SARS. The body temperature of the infected monkeys was monitored three times a day, and blood and fecal samples were periodically collected for specific immunology determinations. On days 7 and 33 after inoculation, necropsies for pathological accessment and pathogen isolation were performed. The four infected macaques developed a fever on days 3 and 4 after inoculation, and maintainted a febrile state for 4-6 days. The highest temperature in the animals recorded was 40.4 degrees C. After a recovery phase, the macaques developed a second febrile condition. Antibody titers against the reovirus injected by the intravenous route occurred in higher number than those in the nasal cavity. Four macaque monkeys demonstrated diffuse alveolar damage, characterized by hemorrhagic pneumonia, serosanguineous exudates, formation of hyaline membranes, and type II pneumocyte hyperplasia, which were similar to those that have been noted in SARS patients. Lymphocytes decreased in the cortex of the lymph node and in the white pulp of the spleen. ReoV was detected in pneumonic tissue by virus isolation and RT-PCR. The macaques infected with the newly isolated reovirus developed a fever, diffuse alveolar damage and pulmonary interstitial inflammation similar to that noted in SARS patients. This evidence demonstrates that ReoV might have a primary role in the etiology of SARS.

Pneumonitis and multi-organ system disease in common marmosets (Callithrix jacchus) infected with the severe acute respiratory syndrome-associated coronavirus

Severe acute respiratory syndrome (SARS) is a significant emerging infectious disease. Humans infected with the etiological agent, SARS-associated coronavirus (SARS-CoV), primarily present with pneumonitis but may also develop hepatic, gastrointestinal, and renal pathology. We inoculated common marmosets (Callithrix jacchus) with the objective of developing a small nonhuman primate model of SARS. Two groups of C. jacchus were inoculated intratracheally with cell culture supernatant containing SARS-CoV. In a time course pathogenesis study, animals were evaluated at 2, 4, and 7 days after infection for morphological changes and evidence of viral replication. All animals developed a multifocal mononuclear cell interstitial pneumonitis, accompanied by multinucleated syncytial cells, edema, and bronchiolitis in most animals. Viral antigen localized primarily to infected alveolar macrophages and type-1 pneumocytes by immunohistochemistry. Viral RNA was detected in all animals from pulmonary tissue extracts obtained at necropsy. Viral RNA was also detected in tracheobronchial lymph node and myocardium, together with inflammatory changes, in some animals. Hepatic inflammation was observed in most animals, predominantly as a multifocal lymphocytic hepatitis accompanied by necrosis of individual hepatocytes. These findings identify the common marmoset as a promising nonhuman primate to study SARS-CoV pathogenesis.

Early enhanced expression of interferon-inducible protein-10 (CXCL-10) and other chemokines predicts adverse outcome in severe acute respiratory syndrome

Background: Exaggerated activation of cytokines/chemokines has been proposed as a factor in adverse outcome of severe acute respiratory syndrome (SARS). Previous studies on chemokines have included only small numbers of patients, and the utility of plasma chemokines as prognostic indicators is unclear.

Methods: We studied 255 archival plasma samples collected during the first or second week after disease onset. The chemokines interferon-inducible protein-10 (IP-10), monokine induced by interferon-γ (MIG), interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), and regulated upon activation normal T cell expressed and secreted (RANTES) were measured by cytometric bead array with a 4-color FACSCalibur flow cytometer. Reverse transcription and real-time quantitative PCR and immunohistochemical staining were performed to analyze the production of IP-10 in lung tissue at autopsy. Conditional logistic regression was used to identify independent predictors for adverse disease outcome.

Results: Increases in IP-10, MIG, and IL-8 during the first week after onset of fever were associated with adverse outcome (intensive care unit admission or death) in the univariate analysis. During the second week, only MIG concentration was associated with prognosis. After adjusting for other risk factors, plasma IP-10 concentration at the first week remained as an independent prognostic factor, with an odds ratio for adverse outcome of 1.52 (95% confidence interval, 1.05–2.55) per fold increase in plasma IP-10 concentration above the median. During the second week, chemokines provided little independent prognostic information. IP-10 was increased in lung tissue from patients who died of SARS.

Conclusions: Increased plasma IP-10 during the first week of SARS symptoms is an independent predictor of outcome. Chemokine activation may be an early event in SARS, and an exaggerated host response may produce complications.

Antibody to severe acute respiratory syndrome (SARS)-associated coronavirus spike protein domain 2 cross-reacts with lung epithelial cells and causes cytotoxicity

Both viral effect and immune-mediated mechanism are involved in the pathogenesis of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) infection. In this study, we showed that in SARS patient sera there were autoantibodies (autoAbs) that reacted with A549 cells, the type-2 pneumocytes, and that these autoAbs were mainly IgG. The autoAbs were detectable 20 days after fever onset. Tests of non-SARS-pneumonia patients did not show the same autoAb production as in SARS patients. After sera IgG bound to A549 cells, cytotoxicity was induced. Cell cytotoxicity and the anti-epithelial cell IgG level were positively correlated. Preabsorption and binding assays indicated the existence of cross-reactive epitopes on SARS-CoV spike protein domain 2 (S2). Furthermore, treatment of A549 cells with anti-S2 Abs and IFN-gamma resulted in an increase in the adherence of human peripheral blood mononuclear cells to these epithelial cells. Taken together, we have demonstrated that the anti-S2 Abs in SARS patient sera cause cytotoxic injury as well as enhance immune cell adhesion to epithelial cells. The onset of autoimmune responses in SARS-CoV infection may be implicated in SARS pathogenesis.

Susceptibility of human and rat neural cell lines to infection by SARS-coronavirus

Pathological characterization of autopsied tissues from patients with SARS revealed severe damage in restricted tissues, such as lung, with no apparent cell damage in other tissues, such as intestine and brain. Here, we examined the susceptibility of neural cell lines of human (OL) and rat (C6) origins to SARS-associated coronavirus. Both of the neural cell lines showed no apparent cytopathic effects (CPE) by infection but produced virus with infectivity of 10^2–5 per ml, in sharp contrast to the production by infected Vero E6 cells of >10⁹ per ml that showed a lytic infection with characteristic rounding CPE. Interestingly, the infection of intestinal cell line CaCo-2 also induced no apparent CPE, with production of the virus at a slightly lower level as that of the Vero E6 cell culture. Notably, the cellular receptor for the virus, angiotensin-converting enzyme 2 was expressed at similar levels on Vero E6 and CaCo-2 cells, but at undetectable levels on OL and C6 cells.

Detection of severe acute respiratory syndrome coronavirus in the brain: potential role of the chemokine mig in pathogenesis

Background. Previous studies have shown that common human coronavirus might be neurotropic, although it was first isolated as a pathogen of the respiratory tract. We noticed that a few patients with severe acute respiratory syndrome (SARS) experienced central nervous symptoms during the course of illness. In the present study, we isolated a SARS coronavirus strain from a brain tissue specimen obtained from a patient with SARS with significant central nervous symptoms.

Methods. Using transmission electronic microscopy and nested reverse transcription–polymerase chain reaction, the causative pathogen was identified in cultures of a brain tissue specimen obtained from the patient with SARS. Histopathologic examination of the brain tissue was performed using the methods of immunohistochemistry analysis and double immunofluorescence staining. Fifteen cytokines and chemokines were detected in the blood of the patient with SARS by means of a bead-based multiassay system.

Results. A fragment specific for SARS human coronavirus was amplified from cultures of the brain suspension, and transmission electronic microscopy revealed the presence of an enveloped virus morphologically compatible with a coronavirus isolated in the cultures. Pathologic examination of the brain tissue revealed necrosis of neuron cells and broad hyperplasia of gliocytes. Immunostaining demonstrated that monokine induced by interferon-Γ (Mig) was expressed in gliocytes with the infiltration of CD68⁺ monocytes/macrophages and CD3⁺ T lymphocytes in the brain mesenchyme. Cytokine/chemokine assay revealed that levels of interferon-Γ–inducible protein 10 and Mig in the blood were highly elevated, although the levels of other cytokines and chemokines were close to normal.

Conclusions. This study provides direct evidence that SARS human coronavirus is capable of infecting the central nervous system, and that Mig might be involved in the brain immunopathology of SARS.

Reduced bone mineral density in male Severe Acute Respiratory Syndrome (SARS) patients in Hong Kong

During the Severe Acute Respiratory Syndrome (SARS) outbreak in Hong Kong in 2003, patients were treated with very high doses of corticosteroid and ribavirin. The detrimental effects of such treatment on the bone mineral density (BMD) of SARS patients are unknown. To compare the BMD of SARS patients with normal range data, a cross-sectional survey was conducted. The bone mineral density of 224 patients with SARS, who were treated with an average of 2753 mg (SD = 2152 mg) prednisolone and 29,344 mg (SD = 15,849 mg) of ribavirin was compared to normal data. Six percent of men had a hip BMD Z score of < or =-2 (P = 0.057 for testing the hypothesis that >2.5% of subjects should have a Z score of < or =-2). Moreover, there was a negative association (r = -0.25, P = 0.023) between the duration of steroid therapy and BMD in men. We conclude that male SARS patients had lower BMD at the hip than normal controls, and this could be attributed to prolonged steroid therapy.

Using siRNA in prophylactic and therapeutic regimens against SARS coronavirus in Rhesus macaque

Development of therapeutic agents for severe acute respiratory syndrome (SARS) viral infection using short interfering RNA (siRNA) inhibitors exemplifies a powerful new means to combat emerging infectious diseases. Potent siRNA inhibitors of SARS coronavirus (SCV) in vitro were further evaluated for efficacy and safety in a rhesus macaque (Macaca mulatta) SARS model using clinically viable delivery while comparing three dosing regimens. Observations of SARS-like symptoms, measurements of SCV RNA presence and lung histopathology and immunohistochemistry consistently showed siRNA-mediated anti-SARS efficacy by either prophylactic or therapeutic regimens. The siRNAs used provided relief from SCV infection–induced fever, diminished SCV viral levels and reduced acute diffuse alveoli damage. The 10–40 mg/kg accumulated dosages of siRNA did not show any sign of siRNA-induced toxicity. These results suggest that a clinical investigation is warranted and illustrate the prospects for siRNA to enable a massive reduction in development time for new targeted therapeutic agents.

An animal model of SARS produced by infection of Macaca mulatta with SARS coronavirus

A new SARS animal model was established by inoculating SARS coronavirus (SARS‐CoV) into rhesus macaques (Macaca mulatta) through the nasal cavity. Pathological pulmonary changes were successively detected on days 5–60 after virus inoculation. All eight animals showed a transient fever 2–3 days after inoculation. Immunological, molecular biological, and pathological studies support the establishment of this SARS animal model. Firstly, SARS‐CoV‐specific IgGs were detected in the sera of macaques from 11 to 60 days after inoculation. Secondly, SARS‐CoV RNA could be detected in pharyngeal swab samples using nested RT‐PCR in all infected animals from 5 days after virus inoculation. Finally, histopathological changes of interstitial pneumonia were found in the lungs during the 60 days after viral inoculation: these changes were less marked at later time points, indicating that an active healing process together with resolution of an acute inflammatory response was taking place in these animals. This animal model should provide insight into the mechanisms of SARS‐CoV‐related pulmonary disease and greatly facilitate the development of vaccines and therapeutics against SARS. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Multiple organ infection and the pathogenesis of SARS

After >8,000 infections and >700 deaths worldwide, the pathogenesis of the new infectious disease, severe acute respiratory syndrome (SARS), remains poorly understood. We investigated 18 autopsies of patients who had suspected SARS; 8 cases were confirmed as SARS. We evaluated white blood cells from 22 confirmed SARS patients at various stages of the disease. T lymphocyte counts in 65 confirmed and 35 misdiagnosed SARS cases also were analyzed retrospectively. SARS viral particles and genomic sequence were detected in a large number of circulating lymphocytes, monocytes, and lymphoid tissues, as well as in the epithelial cells of the respiratory tract, the mucosa of the intestine, the epithelium of the renal distal tubules, the neurons of the brain, and macrophages in different organs. SARS virus seemed to be capable of infecting multiple cell types in several organs; immune cells and pulmonary epithelium were identified as the main sites of injury. A comprehensive theory of pathogenesis is proposed for SARS with immune and lung damage as key features.