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Molecular Psychiatry (1997) 2, 133–136
1997 Stockton Press All rights reserved 1359–4184/97 $12.00
was established in rats with the aim of reproducing and
CYTOKINES IN THE BRAIN
extending the results obtained in humans.
Production of cytokines
Materials and methods
following brain injury:
The patients included in this study had a severe trau-
matic brain injury and were treated according toa stan-
beneficial and deleterious
dardized protocol as previously described.
5–7
CSF and
serum samples were tested by ELISA for interleukin-
for the damaged tissue
(IL)-1, IL-6, IL-8, IL-10, TNF-
a
, transforming growth
factor-beta (TGF-
b
) and nerve growth factor (NGF) as
MC Morganti-Kossman
1
, PM Lenzlinger
1
,
described.
6–8
For the detection of IL-6 in rat serum and
V Hans
1
, P Stahel
2
, E Csuka
1
, E Ammann
1
,
CSF a bioassay was also utilized using 7TD1 cells. The
R Stocker
3
, O Trentz
3
and T Kossmann
3
integrity of the blood–brain barrier (BBB) was deter-
1
Department of Surgery, Division of Research, University
mined by calculating the daily CSF/serum albumin
Hospital Zu
¨
rich, 8091 Switzerland;
2
University of Alabama
quotient (Q
A
).
6
Astrocytes were isolated from newborn
at Birmingham, Department of Microbiology, Birmingham,
mouse brain and stimulated with CSF samples from
Alabama, USA;
3
Division of Trauma Surgery, University
brain-injured patients or with recombinant IL-6 and IL-
Hospital Zu
¨
rich, 8091 Switzerland
8.
6,7
The animal model of diffuse brain injury was
established according to Marmarou et al.
9
A total of 59
animals were used and five animals were killed at each
Keywords: brain injury; interleukins; tumor necrosis factor-
time point from 1 h up to 2 weeks after trauma. The
alpha; transforming growth factor-beta; nerve growth factor;
control group comprised six sham operated animals
astrocytes; acute-phase-response; blood–brain barrier
which were killed after 2 and 24 h.
A profound inflammatory response is initiated immedi-
ately following traumatic brain injury (TBI) and is
Results
characterized by the release of several cytokines with
pro- and anti-inflammatory functions. In order to eluci-
IL-6 and IL-8 were measured in CSF and serum of 22
date which cytokines are released in the human brain in
and 14 patients, respectively. IL-6 concentrations in
response to injury as well as in the peripheral compart-
CSF were found to be 40- to 100-fold higher compared
ment, IL-1, IL-6, IL-8, IL-10, TNF-a and TGF-b were moni-
to serum, during the entire study period.
6
IL-6 reached
tored in CSF and serum of severely brain-injured
the maximal concentration within the first days after
patients. Furthermore, we investigated the possible
trauma and remained elevated during the whole time
modulation of systemic reactions by IL-6 and the ability
of IL-6 and IL-8 to promote the synthesis of nerve
period (see Table 1 for the ranges of cytokines and NGF
growth factor.
in CSF and serum). Since IL-6 is also considered to
Introduction
be the major inducer of the acute phase response, the
concentrations of the acute phase proteins, C-reactive
A traumatic impact to the brain initiates an inflamma-
protein,
a
1-antitrypsin and fibrinogen were measured
tory response characterized by the activation of a num-
in serum. The increase of these proteins correlated
ber of cells and the release of immune mediators which
with the maximal levels of serum IL-6. Interestingly,
may contribute to deleterious secondary brain damage.
IL-6 levels in CSF and serum correlated with each
The kinetics of the release of cytokines and the cell
other when the BBB was dysfunctional as judged by
typesinvolved in cytokine production have been ident-
the Q
A
. On the contrary, no correlation was found
ified in several animal models.
1
As demonstrated in
between CSF- and serum-IL-6 during normal BBB con-
neurological diseases,chronic inflammation within the
ditions.
6
central nervous system (CNS) leads to demyelinating
lesions.
2
On the other hand, increased expression of
Table 1 Ranges of maximal cytokine and NGF concen-
cytokines within the injured brain has also been shown
trations in CSF and serum of brain-injured patients
to trigger neurotrophic factors such as the nerve growth
factor (NGF).
3
Therefore, the evaluation of cytokines
Cytokine or No. of Range of max. Range of max.
may offer further understanding of the pathophysiolog-
NGF patients levels in CSF levels in serum
ical events following TBI.
(pg ml
−1
) (pg ml
−1
)
The objective of our study was to differentiate
between intrathecal and peripheral production of vari-
TNF-
a
36 0.7–757 0–157
ous cytokines by analyzing the CSF and serum of
IL-1 36 0–6.58 0–36.2
patients following isolated, severe brain injury. The
IL-6 22 140–35500 0–1100
secretion of NGF and its dependence on cytokine pro-
IL-8 14 260–8000 0–2400
duction was also analyzed in the CSF of these patients
IL-10 28 0.5–440 1.8–98.5
and in vitro, using mouse astrocytes. An animal model
TGF-
b
20 0.02–5 0–136
NGF 22 0–12000 not done
of diffuse axonal injury, which represents the most
common type of damage in patients with brain injury,
4
Cytokine production after brain injury
MC Morganti-Kossmann
et al
134
The kinetics of IL-8 showed similarities with the IL- 6 and IL-8) seem to be produced within the brain
whereas the release of others in the CSF may account6 kinetics by being always more elevated in the CSF
compared to serum. In addition, maximal concen- for both penetration from the periphery as well as for
intrathecal synthesis (TNF-
a
, TGF-
b
, and IL-10). Theirtrations of IL-8 in the CSF correlated with severe dis-
turbance of the BBB.
8
release persists for a long time period although the
highest levels seem to be present early after injury.NGF was onlydetected in those patientswith highest
IL-6 and IL-8 concentrations in the CSF during the Cytokine production by cells of the CNS is supported
by several works performed either in vitro or in animalstudy period and reached a maximum of 12 ng ml
−1
.
Both cytokines were found to be associated with the models. Moreover, much evidence exists on the ability
of cytokines to modulate not only the functions ofrelease of NGF in the CSF. Furthermore, human CSF
containing IL-6 or IL-8 incubated with cultured mouse immune cells but also of glial cells (reviewed in
Ref. 11).
11
astrocytes induced the production of NGF which was
reduced after preincubation with anti-cytokine anti- The penetration of IL-6 from CSF into serum may
occur as a result of BBB disruption or by an activebodies.
7,8
The animal model of diffuse axonal injury showed a transport mechanism when the BBB is normal.
12
Once
in the periphery, IL-6 may regulate the acute phasesimilar response in terms of IL-6 secretion in CSF and
serum. IL-6 was already detectable in CSF and serum response which was already described in brain-injured
patients.
13
The association of cytokines with the pro-2 h after injury showing a peak at 4 h with a mean con-
centration of 12883 pg ml
−1
(n = 5) and returning to duction of NGF, confirmed by in vitro and in vivo stud-
ies
3,14
indicates that the acute inflammation may alsonormal by 16–24 h. Cytokine levels were always higher
in CSF than in serum as observed in humans. Sham promote the repair of the lesioned CNS in terms ofscar-
ring as well as of axonal regeneration (Figure 1 summa-operated animals used for controls only showed a
minor increase of IL-6 in serum but not in CSF. rizes the possible functions of IL-6 in brain-injured
patients).
15
However, persistent production of cyto-IL-10 was found in the CSF and serum of 28 patients.
Serum concentrations were predominantly higher in kines may also be deleterious for the damaged brain.
16
Cytokines have been identified in a number of central20 patients, CSF levels in seven and one showed simi-
lar levels in both fluids. Peak values of IL-10 in both nervous system disorders such as meningitis, HIV-
infection, multiple sclerosis and Alzheimer’s disease.compartments did not correlate with each other. When
compared to the pattern of IL-6 in the CSF, IL-10 These diseases are often accompanied by gradual loss
of motor, sensory or cognitive functions as a conse-appeared often simultaneously with the initial IL-6
peak and remained at low levels while IL-6 decreased. quence of destruction of neuronal tissue due to an
uncontrolled local inflammation.
17
In this regard, TNF-TNF-
a
was detected in 36 patients. Serum values
were found within the normal range (0–6.3 pg ml
−1
)in
a
seems to have the major cytotoxic properties as com-
pared to the other cytokines and was shown to be syn-19 patients and were elevated in all the others
(maximum of 157.5 pg ml
−1
). CSF concentrations thesized within the plaques in multiple sclerosis
brains.
1
reached 757 pg ml
−1
in 29 individuals and were up to
100-fold higher than serum levels in 11 of them. In Therefore, it becomes of fundamental value that anti-
inflammatory mediators such as TGF-
b
and IL-10 orseven patients no TNF-
a
was detected in the CSF. Sev-
eral peaks characterized the patterns of TNF-
a
in both cytokine-antagonists are secreted in order to minimize
the consequences of a perpetuating inflammatoryfluids for each patient.
TGF-
b
was detected in the CSF and serum of 20 response.
18
IL-6 and IL-8 are two cytokines with plei-
otropic activities which besides their immunologicalpatients. The concentrations of TGF-
b
in serum
remained approximately normal, ranging from 9 and functions seem to play an important role in regener-
ation by increasing neuronal survival. The elucidation104 pg ml
−1
however they increased continuously
toward the end of the study period. In CSF, the highest of the mechanisms underlying this reaction may offer
new therapeutic aproaches with the aim of decreasingpeaks which reached 5003pg ml
−1
were found within
the first 3 days post-trauma. Penetration of this cyto- the incidence of secondary brain damage.
kine through a leakage of the BBB may occur and may
be reflected by the correlation found between the maxi-
Acknowledgements
mal Q
TGF-
b
and Q
A
. However, intrathecal synthesis of
These studies were supported by the Swiss National
TGF-
b
may also take place. In fact, by calculating the
Foundation No. 31.36375.92 and 31.42490.94. The
TGF-
b
index similarly to the IgG index,
10
we found that
authors gratefully acknowledge the work of the staff of
in nine patients this value was greater than the TGF-
b
the intensive care unit of the Division of Trauma Sur-
index calculated in normal individuals. Little or no IL-
gery at the University Hospital, Zu
¨
rich.
1 was detected in both CSF and serum of 36 patients.
References
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