Lung pathology of fatal severe acute respiratory syndrome.

Abstract

Severe acute respiratory syndrome (SARS) is a novel infectious disease with global impact. A virus from the family Coronaviridae has been identified as the cause, but the pathogenesis is still unclear.
Post-mortem tissue samples from six patients who died from SARS in February and March, 2003, and an open lung biopsy from one of these patients were studied by histology and virology. Only one full autopsy was done. Evidence of infection with the SARS-associated coronavirus (SARS-CoV) and human metapneumovirus was sought by reverse-transcriptase PCR and serology. Pathological samples were examined by light and electron microscopy and immunohistochemistry.
All six patients had serological evidence of recent infection with SARS-CoV. Diffuse alveolar damage was common but not universal. Morphological changes identified were bronchial epithelial denudation, loss of cilia, and squamous metaplasia. Secondary bacterial pneumonia was present in one case. A giant-cell infiltrate was seen in four patients, with a pronounced increase in macrophages in the alveoli and the interstitium of the lung. Haemophagocytosis was present in two patients. The alveolar pneumocytes also showed cytomegaly with granular amphophilic cytoplasm. The patient for whom full autopsy was done had atrophy of the white pulp of the spleen. Electron microscopy revealed viral particles in the cytoplasm of epithelial cells corresponding to coronavirus.
SARS is associated with epithelial-cell proliferation and an increase in macrophages in the lung. The presence of haemophagocytosis supports the contention that cytokine dysregulation may account, at least partly, for the severity of the clinical disease. The case definition of SARS should acknowledge the range of lung pathology associated with this disease.

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1773
Summary
Background Severe acute respiratory syndrome (SARS) is a
novel infectious disease with global impact. A virus from the
family Coronaviridae has been identified as the cause, but the
pathogenesis is still unclear.
Methods Post-mortem tissue samples from six patients who
died from SARS in February and March, 2003, and an open
lung biopsy from one of these patients were studied by
histology and virology. Only one full autopsy was done.
Evidence of infection with the SARS-associated coronavirus
(SARS-CoV) and human metapneumovirus was sought by
reverse-transcriptase PCR and serology. Pathological samples
were examined by light and electron microscopy and
immunohistochemistry.
Findings All six patients had serological evidence of recent
infection with SARS-CoV. Diffuse alveolar damage was
common but not universal. Morphological changes identified
were bronchial epithelial denudation, loss of cilia, and
squamous metaplasia. Secondary bacterial pneumonia was
present in one case. A giant-cell infiltrate was seen in four
patients, with a pronounced increase in macrophages in the
alveoli and the interstitium of the lung. Haemophagocytosis
was present in two patients. The alveolar pneumocytes also
showed cytomegaly with granular amphophilic cytoplasm. The
patient for whom full autopsy was done had atrophy of the
white pulp of the spleen. Electron microscopy revealed viral
particles in the cytoplasm of epithelial cells corresponding to
coronavirus.
Interpretation SARS is associated with epithelial-cell
proliferation and an increase in macrophages in the lung. The
presence of haemophagocytosis supports the contention that
cytokine dysregulation may account, at least partly, for the
severity of the clinical disease. The case definition of SARS
should acknowledge the range of lung pathology associated
with this disease.
Lancet 2003; 361: 1773–78. Published online May 16, 2003
http://image.thelancet.com/extras/03art4347web.pdf
Introduction
Since Nov 1, 2002, an outbreak of severe acute
respiratory syndrome (SARS) has affected 33 countries in
five continents, with 7053 reported cases and 506 deaths
at the time of writing.1Local transmission has occurred in
at least six countries. The first cases of SARS in Hong
Kong Special Administrative Region were recognised in
February, 2003. As of May 8, 2003, there had been 1661
cases and 208 deaths in the region.
Clinically, the disease is characterised by fever,
dyspnoea, lymphopenia, and rapidly progressing changes
on radiography.2,3Upper-respiratory-tract symptoms are
not prominent, but diarrhoea has been reported by some
patients. There is no response to conventional antibiotics
used to treat atypical pneumonia. The SARS-associated
coronavirus (SARS-CoV) has been consistently associated
with this disease.3Although this virus seems to be
necessary for the development of SARS, it has not been
localised at the site of lung pathology.3,4Poutanen and
colleagues5found human metapneumovirus (HMPV) as a
second pathogen in patients with SARS and postulated
that HMPV potentiates the progression or severity of
coronavirus infection.
The use of steroids together with ribavirin has been
reported to confer clinical benefit, although randomised
clinical trials to support its clinical efficacy are not
available. To aid understanding of the pathogenesis of the
disease and the relation to current therapy, we report the
pathological and virological findings in six patients with
SARS who died.
Methods
Selection of patients and autopsy material
All patients who met a modified WHO case definition of
SARS6and who underwent lung biopsy or post-mortem
examination during March, 2003, at four major hospitals
in the Kowloon hospital cluster were eligible for inclusion.
The case definition was fever (temperature 38°C or
higher), cough or shortness of breath, new pulmonary
infiltrates on chest radiograph, and either a history of
exposure to a patient with SARS or a lack of response to
empirical antimicrobial coverage for typical and atypical
pneumonia (beta-lactams
quinolones or tetracyclines).3Owing to the potentially
infectious nature of the disorder, full autopsy was done in
only one case. In the other cases, the post-mortem
examination was limited to the lungs. We included only
those patients for whom paired serum samples were
submitted for virological studies during the course of the
illness. Patients with only needle-biopsy samples of organs
available were excluded. During the period under study,
there were six patients with pathological and virological
investigation; one of these also underwent lung biopsy
earlier in the course of the illness.
In all cases the autopsy material was fixed in 10%
neutral buffered formalin and later processed for electron
microscopy. Separate pieces of fresh tissue were sent for
virological study; if sufficient quantity was available, they
were stored at –70°C for immunofluorescence studies.
and macrolides, fluoro-
Lung pathology of fatal severe acute respiratory syndrome
John M Nicholls, Leo L M Poon, Kam C Lee, Wai F Ng, Sik T Lai, Chung Y Leung, Chung M Chu, Pak K Hui, Kong L Mak,
Wilina Lim, Kin W Yan, Kwok H Chan, Ngai C Tsang, Yi Guan, Kwok Y Yuen, J S Malik Peiris
Departments of Pathology (J M Nicholls FRCPA) and Microbiology
(L L M Poon PhD, K H Chan PhD, Y Guan PhD, K Y Yuen FRCPath,
Prof J S M Peiris DPhil), University of Hong Kong, Hong Kong Special
Administrative Region, China; Department of Pathology and
Medicine, Princess Margaret Hospital, Kowloon (K C Lee FRCPath,
S T Lai FHKAM); Department of Pathology, Yan Chai Hospital,
Kowloon (W F Ng FRCPath); Departments of Pathology
(C Y Leung FRCPath) and Medicine (C M Chu MRCP), United Christian
Hospital, Kowloon; Department of Pathology, Kwong Wah Hospital
(P K Hui FRCPath, K L Mak FRCPath); Government Virus Unit, Kowloon
(W Lim FRCPA); and Departments of Pathology (K W Yan FHKAM) and
Microbiology (N C Tsang FRCP), Queen Elizabeth Hospital, Kowloon
Correspondence to: Prof J S Malik Peiris, Department of
Microbiology, University of Hong Kong, Pok Fu Lam, Hong Kong
Special Administrative Region, China
(e-mail: malik@hkucc.hku.hk)

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Patients
Patient 1, a 37-year-old woman, had good health before
the illness. She was admitted on March 13, 2003, with a
history of fever, cough, and general muscle pain for
10 days. Oxygen saturation on admission was 89% on
50% oxygen. The chest radiograph showed patchy
haziness. The patient soon developed respiratory failure
necessitating mechanical ventilation; ribavirin and
antibiotic treatment was then started. The ratio of partial
arterial pressure of oxygen (PaO2) to fraction of inspired
oxygen (FiO2) was 24·2 kPa on the day before death. She
died on March 23, after 10 days of assisted ventilation.
Patient 2, a 39-year-old woman who was previously
well, had indirect contact with a person who developed
fever after return from Guangzhou, China. She
subsequently developed fever with shortness of breath and
diarrhoea. She had lymphopenia at admission, and the
chest radiograph showed infiltrates in the left upper zone.
Treatment with ribavirin and steroids was started on
March 21. She developed respiratory failure the next day
and was intubated. She had repeated cardiac arrests and
died on March 24.
Patient 3, a 64-year-old man, developed influenza-like
symptoms and left pleuritic chest pain on Feb 15. A chest
radiograph taken a day later showed haziness in the left
lower zone. He subjectively improved after self-medication
with levofloxacin and penicillin. He visited Hong Kong on
Feb 21 as a tourist, but his condition then deteriorated. He
was admitted directly to the intensive-care unit and
intubated on Feb 22. Investigation showed diffuse bilateral
ground-glass changes on chest radiograph and severe
oxygen desaturation. Despite empirical antimicrobial
coverage for typical, atypical, and hospital-acquired
pneumonia, his condition continued to deteriorate. He was
empirically treated with oseltamivir, foscarnet, intravenous
immunoglobulin and, at a later stage, ribavirin and
steroids. After ventilation for 10 days with a peak airway
pressure of 36 cm water, tidal volume of 730 mL, and
PaO2/FiO2 9·8 kPa, he died on March 4 with acute
respiratory distress syndrome and multiorgan failure.
Patient 4 was a 53-year-old man with a history of
hypertension. He had developed influenza-like symptoms
a few days before admission on Feb 28 with chest
radiographic changes of diffuse bilateral pneumonia and
respiratory failure. He did not respond to doxycycline,
amantadine, and cefotaxime. An open lung biopsy was
done on March 4. Routine microbiological and virological
investigations were negative. He was empirically treated
with oseltamivir, steroids, and ribavirin. Non-oliguric
renal failure developed and was later complicated by
nosocomial pneumonia due to Pseudomonas aeruginosa.
He died on March 19, after ventilation for 16 days with a
peak airway pressure of 34 cm water, tidal volume of
640 mL, and PaO2/FiO217·0 kPa
Patient 5 was a 49-year-old businessman who had a
history of hepatitis B liver cirrhosis and portal hypertension.
He developed influenza-like symptoms while in Hong Kong
but still travelled overseas on Feb 26. Investigation at his
destination showed lymphopenia and thrombocytopenia in
the peripheral blood examination, and bilateral pulmonary
infiltrates on chest radiograph. He went into respiratory
failure on March 2, and on March 5 was transferred back to
Hong Kong, where he was ventilated. The ventilation
pressure was 20/10 cm water most of the time. Positive
end-expiratory pressure was 15–17 cm water. The tidal
volume was generally kept at 450–650 mL, and the PaO2
was between 70% and 90% and FiO2between 80% and
100%. His renal function deteriorated progressively from
March 9 to March 12, and at the time of death the urea
concentration was 10·6 mmol/L and creatinine 218 µmol/L.
Total bilirubin varied between 18 µmol/L and 27 µmol/L.
Despite intensive support and antimicrobial coverage with
piperacillin-tazobactam, azithromycin, and oseltamivir, he
died on March 13.
Patient 6 was a 77-year-old man with good health
previously. On March 2 he was admitted to hospital for
increasing shortness of breath, fever, and cough for
Patient Coronavirus serology RT-PCR on
nasopharyngeal
aspirate before
death
RT-PCR on
post-mortem lung
DateTitre Corona-
virus
NA
HMPV Corona-
virus
–
HMPV
1 March 14
March 23
March 19
March 24
Feb 26
March 3
March 3
March 11
March 6
March 11
March 4
March 11
1/40
1/640
1/10
1/640
1/50
1/200
1/200
1/1600
<1/50
1/800
1/50
1/1600
NA–
2 NANA+–
3+–+–
4+–+–
5+–––
6+–+–
NA=not available
Table 1: Virological investigations of patients with fatal SARS
Figure 1: Open lung biopsy from patient 4
Arrow shows an enlarged pneumocyte with amphophilic granular
cytoplasm and prominent nucleolus. Haematoxylin and eosin; ?400.
Figure 2: SARS showing hyaline-membrane formation and
pneumocyte desquamation with focal giant-cell formation
Haematoxylin and eosin; ?400.

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Routine microbiological investigations included culture
of blood and sputum for bacterial pathogens.3Serology
was done with complement-fixation tests for respiratory
viruses, chlamydiae, and Mycoplasma pneumoniae.
Total RNA and DNA
nasopharyngeal aspirates with the Viral RNA minikit and
QIAmp DNA minikit (QIAGEN, Hilden, Germany).
Reverse-transcriptase (RT) PCR was done for influenza A,7
adenovirus,8HMPV, and a newly recognised coronavirus
subsequently reported to be associated with SARS.3The
RT-PCR protocol has been described previously.3
The biopsy sample or post-mortem lung tissue was
homogenised in a tissue grinder, and the supernatant was
inoculated onto cell cultures. Viral RNA was extracted
from the tissues with the RNeasy minikit (QIAGEN)
according to the manufacturer’s
instructions. RT-PCR for the novel coronavirus and for
HMPV was carried out as described above.
Serial dilutions of serum from acute and convalescent
patients were tested in parallel for antibodies to the
coronavirus and HMPV by an indirect immunofluore-
scence test on FRhK-4 cells infected with the respective
virus.3
were extracted from
tissue protocol
Role of the funding source
The sponsors of the study had no role in the study design,
data collection, analysis, or interpretation, or in the
writing of the report.
Results
Ante-mortem investigations for routine bacterial and viral
respiratory pathogens proved unremarkable. However, all
six patients had four-fold or greater rises in antibody titre
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2
consolidations of lower zones on chest radiograph and
oxygen desaturation. He was intubated and ventilated by
positive end-expiratory pressure mode in the intensive-care
unit 2 days after admission. His clinical course was
complicated by pneumonia due to meticillin-resistant
Staphylococcus aureus. He was ventilated for 12 days with a
peak airway pressure of 30 cm water, tidal volume of
540 mL, and PaO2/FiO2 9·4 kPa, but he died on
March 15, despite extensive antimicrobial coverage for
typical, atypical, and hospital-acquired pneumonia.
The clinical presentations of two of these patients
(patients 3 and 4) have been reported previously.2
days. Investigations showed bilateral patchy
Investigations
Only one patient (patient 4) had an open lung biopsy
done before death. The material was divided into four
pieces; one was sent for viral studies, one frozen at –70°C,
one fixed in formalin, and the one fixed in 2·5%
glutaraldehyde. The latter was processed for transmission
electron microscopy.
For immunohistochemistry, paraffin-embedded blocks
of the lung tissue were sectioned at 5 µm and dewaxed by
standard procedures. Monoclonal antibodies (Dako,
Carpintaria, CA, USA) to keratin AE1/3 (1:50), CD3
T-cell (1:5), and CD68 macrophage marker (1:50) were
applied on each section, and staining was done with the
Ventana Nexes automated immunohistochemical stainer.
Frozen post-mortem lung tissue from one patient
(patient 5) was available for study. Cryostat sections were
stained with directly conjugated monoclonal antibodies to
influenza viruses A and B, adenovirus, and parainfluenza
virus (Dako, USA) and examined under a Nikon Eclipse
E800M fluorescent microscope.
PatientSexAge
(years) onset
Date of Date of
hospital
admission
Date of
death
Diffuse
alveolar cells
damage
Giant Cytomegaly Other pathological
with
granular
eosinophilic
cytoplasm
Other medical
disordersfindings
1
2
Female
Female
37
39
March 3
March 16 March 19
March 13March 23
March 24
+
+
–
–
+
–
Epithelial denudation
Squamous metaplasia with loss of cilia,
haemophagocytosis
Epithelial denudation with fibrin thrombi
present in pulmonary vessels
Bronchiolitis obliterans
Epithelial denudation, white-pulp atrophy
in spleen
Haemophagocytosis
None
None
3Male 64Feb 15Feb 22 March 4+ +++None
4
5
Male
Male
53
49
Feb 23
Feb 24
Feb 28
March 5
March 19
March 13
+
+
++
++
+
+
Hypertension
Cirrhosis with oeso-
phageal varices
None6
Table 2: Summary of histological findings
Male 77 Feb 28March 2March 15 ++++
Figure 3: SARS-CoV pneumonia with cytomegaly of pneumocytes
Haematoxylin and eosin; ?400.
Figure 4: CD68 macrophage antibody staining of giant cells in
patient 5
Diaminobenzidine with haematoxylin counterstain; ?400.

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to the SARS-CoV, indicating recent infection with this
virus (table 1). In addition, several patients had evidence
of coronaviral RNA in the nasopharyngeal aspirate, and in
one case (patient 4) also in the plasma. Viral RNA was
found in the lung biopsy sample of patient 3. No evidence
of HMPV infection (rise in antibody titre or viral RNA)
was found in any of the patients studied (table 1).
Evidence of SARS-CoV RNA was detected in the post-
mortem lung samples of four patients by RT-PCR. None
of these samples had evidence of HMPV RNA.
In the biopsy sample from patient 4, most of the
material was pleural tissue with a small amount of lung
parenchyma. The architecture was preserved with a mild
increase in interstitial lymphocytes. Cytomegaly was
present in a very few pneumocytes; it was characterised by
nuclear enlargement, prominent
amphophilic granular cytoplasm (figure 1). No typical
viral inclusions were identified. There was a mild to
moderate increase in alveolar macrophages and early
hyaline-membrane formation.
Gross findings in the post-mortem lung tissue were
similar among patients (table 2). Where the lungs were
removed en bloc, they weighed 1000–2100 g and were
oedematous, with a greyish brown consolidated cut
surface. The consolidation was irregular and patchy, with
foci of pale tissue measuring up to several millimetres in
diameter. More diffuse involvement was seen in one case
(patient 4); mucopurulent material was seen in the
tracheobronchial tree.
In cases of disease duration of less than 10 days, the
histological involvement of the lung varied, with a mixed
inflammatory infiltrate, oedema, and hyaline-membrane
formation seen (figure 2; table 2). The intra-alveolar
oedema was granular or vacuolated. Desquamation of
pneumocytes was a prominent and consistent feature
(figure 3).
All cases showed scattered single enlarged cells that, in
most, were associated with large nuclei and prominent
nucleoli, similar to the findings in the open lung biopsy
sample. Clearing of the chromatin was also seen. Giant-
cell formation was seen within the alveolar lumen in four
cases, and there were a few cells that contained
amphophilic to basophilic cytoplasmic granules within
enlarged pneumocytes. One patient (patient 3) showed
fibrin thrombi within pulmonary vessels, and another
(patient 1) showed intimal swelling of pulmonary
vessels. In three of four cases, the giant cells were
nucleolus, and
Figure 5: Squamous metaplasia of bronchial mucosa in SARS-
CoV pneumonia
Haematoxylin and eosin; ?400.
Figure 6: Septal inflammation of patient 2
A: Increased numbers of mononuclear cells with haemophagocytosis.
Haematoxylin and eosin; ?400. B: The mononuclear cells are CD68
positive. Diaminobenzidine with haematoxylin counterstain.
Figure 7: Thin-section electron micrograph showing a dilated
secretory vesicle containing a 90 nm coronavirus particle
?63 000.

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cytoplasm. We therefore hypothesise that this cytoplasmic
amphophilia may be due to viral assembly within the
Golgi apparatus—a feature seen on electron microscopy
of the open lung biopsy sample from patient 4.3
The histological changes of uncomplicated viral
pneumonias are rarely described, and reports tend to be
derived from post-mortem examination of patients who
succumb to the pneumonia; thus, they may not be
representative of the majority of pneumonia patients, who
survive.3,15The same is true for SARS, because the
patients admitted to hospital have not been in a suitable
medical condition to warrant biopsy. However, several
features of fatal coronaviral pneumonia can be identified.
Coronavirus infection in the early stages seems to
stimulate epithelial cells and results in cellular
proliferation and squamous metaplasia in the lung. This
type-2 pneumocyte hyperplasia and hypertrophy has also
been identified with porcine reproductive and respiratory
syndrome virus (an arterivirus tentatively classified under
the Coronaviridae16) as well as porcine respiratory
coronavirus (previously
gastroenteritis virus, respiratory variant). In those
infections mild type-2 pneumocyte proliferation is
associated with squamous metaplasia.17
macrophage proliferation is more prominent in the
consolidated areas of the lung; this distribution is also
seen with porcine respiratory coronavirus.18
In contrast to typical diffuse alveolar damage in which
neutrophils and fibroblasts are the main cellular agents
and macrophages have a lesser role,9in patients with fatal
SARS macrophages are the prominent leucocyte in the
alveoli, even in the early stages of the disease. The finding
of haemophagocytosis in the lung and white-pulp atrophy
of the spleen identified in SARS is reminiscent of that
reported in fatal influenza subtype H5N1 disease in
1997.19
Haemophagocytosis has been attributed to
cytokine dysregulation.20Lymphopenia is another feature
common to both SARS-CoV and H5N1 influenza
pneumonia.21Both viruses have crossed to human beings
from animals or birds.3,21Experimental studies in which
macrophages are infected in vitro suggest that, compared
with conventional human influenza viruses, the subtype
H5N1 influenza A viruses isolated in 1997 are
hyperinducers of proinflammatory cytokines.22Human
coronavirus OC43 can replicate in human macrophages in
vitro.23Taken together, the similarity of clinical and
pathological changes in SARS-CoV pneumonia and
H5N1 pneumonia suggest that proinflammatory cytokines
released by stimulated macrophages in the alveoli have a
prominent role in pathogenesis of SARS, resulting in
cytokine dysregulation. This idea has implications for the
management of coronaviral pneumonia. Intervention with
steroids might modulate this cytokine response and
prevent a fatal outcome, as has been proposed for non-
viral acute respiratory distress syndrome.24
Although we did not find PCR evidence of a secondary
viral infection, such as HMPV, in pigs infected with some
isolates of porcine respiratory coronavirus, the respiratory
lesions were severe enough to predispose the pigs to
secondary bacterial or mycoplasmal infections or to lead
to combined viral infections.25As we have already
mentioned, the histological
reproductive and respiratory syndrome virus infection are
similar to those of SARS-CoV infection; it is possible that
SARS-CoV infection in human beings may “open the
door” to secondary infections, as previously reported.5
The patients who received ribavirin therapy still had PCR
and electron-microscopic evidence of SARS-CoV in the
lung. This finding supports clinical evidence that a search
known as transmissible
In SARS,
features of porcine
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positive for the macrophage marker CD68 (figure 4); in
one case, they were positive for the epithelial marker
AE1/3. In the patient who had frozen tissue available, no
staining was identified to adenovirus, parainfluenza
virus, or influenza viruses A or B on frozen-section
immunofluoresence.
One patient, in whom the time from onset of
symptoms to death was 8 days, showed squamous
metaplasia of the bronchi with loss of cilia (figure 5). In
addition, within the parenchyma and also within the
interstitium there were increased numbers of CD68-
positive mononuclear cells and focal haemophagocytosis
(figure 6). Because of the risk of infection, most post-
mortem examinations were limited to the chest, but in
patient 5, for whom a full autopsy was done, pronounced
white-pulp atrophy of the spleen was seen. In this case,
electron microscopy showed dilated Golgi apparatus in
the cytoplasm of pneumocytes, and within these
organelles, 90 nm viral particles with small external
spikes corresponding to coronavirus were identified
(figure 7). These particles were of similar morphology to
those reported previously.3
Discussion
All of the six patients described had serological evidence
of recent infection with the SARS-CoV. Five had evidence
of viral RNA detectable in samples taken before or after
death. In previous studies, healthy controls and patients
with unrelated disease had no evidence of SARS-CoV
antibody or RNA in the serum or the respiratory tract,
respectively.3
In patients with disease of duration less than 10 days
there was hyaline-membrane formation, pneumocyte
proliferation, and oedema. Diffuse alveolar damage was
seen in cases of longer duration. This diffuse alveolar
damage typically goes through an exudative phase
followed by a proliferative phase,9although others have
described a three-stage process: an inflammatory or
exudative phase, a proliferative phase, and a final fibrotic
phase.10Viral infections resulting in diffuse alveolar
damage typically fall into two categories; influenza viruses
A and B and adenovirus cause most cases of viral
pneumonia in immunocompetent adults. Immuno-
compromised hosts are susceptible to pneumonias caused
by cytomegalovirus and other herpesviruses, measles
virus, and adenovirus.11In addition to the diffuse alveolar
damage here, morphological features of giant cells and
pneumocyte hyperplasia, which appear to be prominent in
this viral infection, were seen in these patients.4,12
Multinucleate giant cells within the alveoli have previously
been reported in patients with SARS,4,12
derivation has remained unclear. We have documented
that in three of the patients these giant cells are of
macrophage origin and in one other patient they are
epithelial in origin. These giant cells were not present in
the ante-mortem lung biopsy sample and were present
only in patients with disease progression for longer than
8 days from admission. Some animal coronaviruses
induce syncytium formation in cell culture,13and SARS-
CoV also induces focal syncitium formation4in Vero cells.
Bronchial epithelial denudation, loss of cilia, and
squamous metaplasia were early features. Another notable
feature was the presence of large pneumocytes showing an
enlarged nucleus and granular amphophilic cytoplasm.
These changes were also seen in the open lung biopsy
sample from patient 4. Coronavirus assembly takes place
in the Golgi apparatus of the cytoplasm;14in the sections
of the coronavirus-infected culture this process was
characterised by swelling and increased granularity of the
but their