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1 From the Department of Ophthalmology and Departments of 2 Cell and Developmental Biology, and 3 Medicine, Casey Eye Institute, Oregon Health Sciences University, Portland, Oregon.
| Abstract |
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(TNF-
) in the induction of uveitis by a reverse passive
Arthus reaction (RPAR). METHODS. Human serum albumin (HSA) antiserum was injected into the vitreous of "knockout" or "double knockout" mice genetically deficient in IL-1 receptor type I (IL-1RI-/-), TNF receptors p55 and p75 (TNFR p55-/-/p75-/-), IL-1RI and TNFR p55 (IL-1RI-/-/TNFR p55-/-), and controls. Twenty-four hours later, animals were challenged with intravenous HSA. Eyes were enucleated 4 hours after antigen challenge, and inflammation was quantitated by counting cells on histologic sections. Interleukin-6 in aqueous humor was measured with a B9 cell bioassay. The distribution of immune complexes in eyes was observed by immunohistochemical staining for IgG and complement component C3.
RESULTS. Four hours after antigen challenge, immune complexes were localized at the ciliary body and iris of receptor-deficient mice. A transient uveitis was most severe at this time. A significant reduction in the median number of infiltrating cells was found in TNFR p55-/-/p75-/- mice (4.8, n = 15), compared with controls (14.2, n = 20, P < 0.05). The median number of infiltrating cells was significantly reduced in IL-1RI-/- mice (knockout 2.6, n = 11; controls 7.4, n = 8, P < 0.005). Interleukin-1RI-/-/TNFR p55-/- mice had a strong reduction in infiltrating cells (knockout 1.6, n = 11; controls 27.3, n = 12, P = 0.002). Interleukin-6 activity in aqueous humor was reduced in IL-1RI-/-/TNFR p55-/- mice (P = 0.03) but not in TNFR p55-/-/p75-/- (P = 0.40) mice. Most IL-1RI-/- mice had no detectable aqueous humor IL-6, but this group was not statistically different from controls.
CONCLUSIONS. In contrast to endotoxin-induced uveitis, both IL-1 and TNF appear to have critical roles in RPAR uveitis. When receptors for these cytokines were deleted, the severity of immune complexinduced uveitis was profoundly reduced.
| Introduction |
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The formation of immune complexes and their local deposition
triggers an inflammatory cascade that leads to tissue injury and
ensuing morbidity and mortality. An experimental model of immune
complexmediated pathogenesis was described nearly a century ago by
Arthus.1
It was originally characterized by edema,
hemorrhage, and infiltration of acute inflammatory leukocytes,
specifically neutrophils. Because of its ease and reproducibility, the
experimental variant most commonly used now is the reverse passive
Arthus reaction. Local injection of antibodies and intravenous
injection of antigen results in the local formation of immune complexes
and its consequences. Immune complextriggered inflammation may be
initiated by cell-bound Fc receptors or by activation of
complement.2
3
The response may then be amplified by
paracrine mediators including several cytokines4
5
and
neuronal products such as substance P.6
The relative
importance of cell activation via immune complexes binding to Fc
receptors versus complement activation is tissue specific. Complement
activation appears to be dominant in the lung7
8
; whereas
signaling via Fc
receptors is necessary in a model of autoimmune
glomerulonephritis.9
Both mechanisms are important for
immune complexinduced inflammation in the skin and
peritoneum.7
There is similar evidence indicating that the
cytokine requirements for immune complexinduced inflammation is also
tissue specific. Both interleukin-1 (IL-1) and tumor necrosis
factor-
(TNF-
) are necessary in alveolitis; however, in dermal
vasculitis IL-1, and not TNF
, is required for full expression of
tissue injury.4
5
Several cytokines have been described as inflammatory mediators in the
eye. In particular IL-1, IL-2, IL-4, IL-6, TNF-
, and transforming
growth factor-ß (TGF-ß) have been detected in aqueous and vitreous
humors from a number of acute and chronic ocular disorders, including
uveitis.10
11
12
13
Soluble immune complexes,14
15
aggregated IgG,15
16
monomeric Fc
fragments,17
and IgG-coated sheep red blood
cells18
have been reported to stimulate secretion of IL-1,
TNF
, IL-6, IL-10, and prostaglandin by murine or human monocytes and
macrophages.
The biological activities of IL-1 and TNF-
suggest that each
could be a key mediator in the development of uveitis. Intravitreal
injection of human TNF-
or IL-1
in rabbit eyes induced leukocyte
infiltration and protein leakage.19
20
21
However, studies
of uveitis induced by intravitreal injection of endotoxin
(lipopolysaccharide) have not consistently confirmed the involvement of
TNF-
and IL-1 in the initiation of this inflammatory processes.
Rosenbaum and Boney22
showed that administration
of a human IL-1 receptor antagonist (IL-1ra) did not block
endotoxin-induced uveitis (EIU) in rabbits. Likewise, inhibitors of
TNF-
failed to block EIU.23
24
25
26
Some of these reports
indicated that TNF-
inhibition exacerbated this inflammatory
response.23
26
More recently we reported that in mice the
ocular inflammatory response to intravitreal endotoxin was not affected
by the lack of TNF receptors.27
28
The biological activities of IL-1 and TNF-
are mediated by receptors
present on the cell surface. Transmembrane signaling of the type I IL-1
receptor is stimulated on binding of IL-1
or IL-ß. The type II
IL-1 receptor seems to act as an inhibitor of IL-1 because binding to
this receptor does not appear to initiate transmembrane
events.29
30
There are two known receptors for TNF, and they are coexpressed on most
cell types. These are the 55 to 60 kDa TNFR-I (p55) and the 70 to 80
kDa TNFR-II (p75). In the past, TNF-induced cytotoxicity was attributed
solely to the p55 receptor, whereas TNF-induced proliferation was
attributed to the p75 receptor.31
32
However, many recent
papers have shown that p75 can greatly enhance p55-induced cell
death.33
34
35
36
In particular, membrane-bound TNF-
appears
to be the primary ligand for p75 and can cause cytotoxicity in cells
that are not affected by soluble TNF-
.34
Previous studies showed that TNFR p55-/-/p75-/- mice are protected against a normally lethal regimen of D-galactosamine and endotoxin injections. Similar results were found with TNFR p55-/- mice but not with p75-/- mice.37 However, other reports have shown that the TNFR p75-/- mice develop an exacerbated febrile response after high doses of endotoxin.38 Using a pulmonary inflammation model, Peschon et al.37 showed that the initial pulmonary influx of neutrophils in response to M. faeni is dramatically decreased in mice lacking either p55 or p55 and p75 TNF receptors, but exacerbated in TNFR p75-/- mice.37 All these studies indicate a differential role for TNF receptors in inflammation.
The present work investigates the role of TNF and IL-1 in the pathogenesis of immune complexinduced uveitis. Leukocyte infiltration and IL-6 levels were evaluated in mice in IL-1R1-/-, TNFR p55-/-/p75-/-, and IL-1R1-/-/TNFR p55-/- mice and their controls. The results indicate that both cytokines, IL-1 and TNF, play an important role because the absence of receptors for either cytokine causes profound inhibition of reverse passive Arthus reaction (RPAR) uveitis.
| Materials and Methods |
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All mice were provided food and water ad libitum and were kept on a 12 hour light-dark cycle. All experiments were conducted in accordance with the ARVO Statement on the Use of Animals in Opthalmic Research.
RPAR-Induced Uveitis
Uveitis was induced in 6- to 8-week-old
IL-1R1-/-, TNFR
p55-/-/p75-/-, and
IL-1R1-/-/TNFR p55-/- mice
and controls by bilateral intravitreal injection of 2 µl of
heat-inactivated serum (57°C, 30 minutes) from mice immunized earlier
with 100 µl of an emulsion containing 50% 10 mg/ml human serum
albumin (HSA; Buminate 25%; Baxter Healthcare Corporation, Glendale,
CA) in saline and 50% TiterMax Gold (CytRx, Norcross, GA). Blood was
collected 4 to 6 weeks after immunization by cardiac puncture to
minimize endotoxin contamination of the serum. The HSA antiserum
contained less than 0.05 U/ml of endotoxin (E-Toxate; Sigma, St. Louis,
MO). The intravitreal injections were given with a 27-gauge needle.
Twenty-four hours later, animals were challenged intravenously with HSA
(1.5 mg/g of body weight). Eyes were enucleated for quantification of
inflammation after 4 hours. One eye from each animal was fixed in 10%
neutral-buffered formalin (Richard-Allan, Richland, MI), embedded in
paraffin, and sectioned for histologic analysis. Aqueous humor was
collected from the contralateral eye and centrifuged briefly at
10,000g. Two-microliter aliquots of the supernatants were
diluted in 60 µl of saline containing 0.25% HSA and kept frozen
until they were assayed for IL-6 bioactivity. Mice receiving saline
instead of HSA antiserum or HSA were used as internal controls.
Inflammation was quantified by determining the mean number of infiltrating cells in the aqueous and vitreous humors of 5 hematoxylin and eosinstained sections per each eye. One sagittal section including the optic nerve head and two sections at either side of it were selected from each eye. Sections from these locations usually contained the highest number of infiltrating cells.
IL-6 Bioassay
Interleukin-6 activity in aqueous humor was determined by
measuring [3H]thymidine incorporation in a
murine B9 cell bioassay as described.42
43
The sensitivity
of the assay was approximately 0.2 pg/ml for recombinant mouse IL-6
(specific activity of 1.2 x 107 U/mg;
PharMingen, San Diego, CA).
Immunohistochemistry
Five-micrometer tissue sections were immunostained for immune
complexes with anti-mouseIgG polyclonal antibody (1:100,000; Sigma
Chemical) and anti-C3c polyclonal antibody (1:1000; NORDIC Immunologic
Laboratory, Tilburg, The Netherlands) with an alkaline phosphatase
detection system. Briefly, sections were deparaffinized and incubated
with blocking normal serum of the same species as the secondary
antibody. Sections were incubated with the primary antibody overnight
at 4°C, washed in TBS (50 mM Tris, pH 7.5, 0.15 M NaCl) plus 0.5%
Tween-20 and incubated for 1 hour at room temperature with biotinylated
anti-IgG secondary antibody. After washing with TBS, the sections were
incubated with avidin-biotin conjugated to alkaline phosphatase and
then washed again. Fast Red (Biogenex, San Ramon, CA) was used as
chromogen. Counterstaining was done with hematoxylin.
Statistical Analysis
Statistical significance was evaluated by using a one-tailed
unpaired MannWhitney test. P < 0.05 was considered
to be statistically significant. Results are presented as the median of
the sample group.
| Results |
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,
or both. To test these possibilities, intraocular RPAR was induced in
mice genetically deficient in receptors for one or both of these
cytokines. The severity of uveitis was scored by histologic examination
4 hours after the intravenous injection of HSA. Mice lacking TNFR p55
and p75 showed significantly less inflammation than controls (Figs. 3
and 4)
. The median score decreased from 14.2 cells/section (n = 20) in the controls to 4.8 cells/section (n = 15,
P < 0.05) in knockout mice.
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| Discussion |
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in the ocular Arthus reaction. Mice
from all three knockout lines had significantly fewer (less than a
third) infiltrating cells than their corresponding controls. The
dependency on both IL-1 and TNF-
is similar to that reported for
immune-complex induced alveolitis but not dermal
vasculitis.4
5 Control groups in studies shown in Figures 4 5 and 6 showed differences in median cellular response. These differences reflect the biological variability inherent in the model and are not statistically significant. Receptor-knockout animals and their controls are tested simultaneously such that variables such as antiserum lot, injection technique, or stress in the animal care facility are well matched. In our studies, however, if one elects to combine all results for controls, one still finds a statistically significant reduction in inflammation for each knockout line studied. The C57BL/6x129sv F1 mice used for this work are not ideal controls for the genetically altered mice, which are progeny of random C57BL/6x129sv F2 hybrids. Nonetheless, other laboratories have published results with the F1 controls,39 and they were used in our EIU studies discussed below. The reduction of inflammation in all three knockout lines tested, despite their differing mix of C57BL/6 and 129sv genes, supports the contention that this reduction is due to the receptor deficiency and not genetic background.
Our results with RPAR uveitis differ from those previously obtained for uveitis induced by intravitreal injection of endotoxin in these same receptor-deficient mouse lines.28 The severity of uveitis measured in those EIU studies was not altered by deletion of TNFR p55 and p75 and was inconsistently reduced by deletion of IL-1R1. Lack of both IL-1R1 and TNFR p55 had the most profound effect. The data from the two studies support the hypothesis that uveitis resulting from different agents can be differentially dependent on the action of an individual cytokine. These differences suggest that RPAR uveitis and EIU follow some different pathways during the inflammatory response in the eye.
The deposition of immune complexes was confirmed by the detection of IgG and C3 component, with the characteristic distribution in the ciliary body, iris, and Bruchs membrane. Although the production of other complement factors, such as C5a, was not measured, there is no a priori reason to suspect that they would be directly altered in these mice. A major question in the induction and progression of uveitis is how foreign antigens get into the uveal tissue and induce disease. A central event may be the deposition of antigen from the circulation into the eye. It has been proposed that uveitis may result from an anatomic predisposition of the uveal tract to in situ immune complex formation. Fenestrated capillaries and anionic sites within the ciliary body, ciliary processes, and Bruchs membrane provide a system that, like the glomerulus, is selectively permeable, retaining molecules of a given size and charge. Circulating antibodies may exit the vasculature within the ciliary body and choroid and then selectively combine with antigens to form immune complexes.44 45 46 Formation of the immune complexes within the eye may be an important factor. Mice that had been injected with preformed immune complexes, some of which were deposited in ocular vessels, did not get uveitis.47 Likewise, only a small percentage of patients with systemic lupus erythematosus develop uveitis.48
Clinically anterior uveitis is a diverse collection of diseases. For example, the uveitis associated with ankylosing spondylitis differs from that associated with juvenile rheumatoid arthritis, which in turn differs from that associated with inflammatory bowel disease.49 Different mediators are likely to contribute to clinically distinct subsets of anterior uveitis. Our results strongly support this hypothesis by demonstrating a role for TNF in immune complexdependent anterior uveitis, whereas five previous studies have failed to show a role for TNF in endotoxin-induced anterior uveitis.23 24 25 26 28
| Acknowledgements |
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| Footnotes |
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Submitted for publication October 6, 1998; revised April 23, 1999; accepted June 23, 1999.
Commercial relationships policy: N.
4 Present address: Venezuelan Institute for Scientific Research (IVIC), Caracas, Venezuela. ![]()
Presented at the annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Florida, May, 1998.
Corresponding author: Stephen R. Planck, Casey Eye Institute, Oregon Health Sciences University, 3375 SW Terwilliger Boulevard, Portland, OR 97201-4197. E-mail: plancks{at}ohsu.edu
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and IL-1 J Immunol 149,331-339[Abstract]
) in endotoxin-induced uveitis Invest Ophthalmol Vis Sci 34,2911-2917
is not a major mediator of endotoxin-induced uveitis: studies in cytokine receptor deficient mice J Rheumatol 25,2408-2516[Medline][Order article via Infotrieve]
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