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1 From the National Eye Institute, National Institutes of Health; and 2 the Howard Hughes Medical Institute-National Institutes of Health Research Scholars Program, Bethesda, Maryland.
| Abstract |
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METHODS. Conventional technologies were used to generate three lines of
transgenic (Tg) mice, expressing hen egg lysozyme (HEL) under the
control of the
A-crystallin promoter. To induce intraocular
inflammation, these Tg mice were injected with lymphocytes from
syngeneic wild-type donors sensitized against HEL. Before their
injection, the cells were stimulated in culture with HEL. To release
lenticular material, some eyes were capsulotomized. Ocular
histopathologic changes were examined by routine methods. Levels of HEL
antibody were measured by enzyme-linked immunosorbent assay, whereas
cellular immunity was determined by the lymphocyte proliferation assay.
RESULTS. Intraocular inflammation developed in HELTg mice injected with syngeneic lymphocytes sensitized against HEL. The severity of inflammation was directly related to the number of injected cells, as well as to the accessibility of HEL. The most intense inflammation was seen in Tg mice in which the lens was disintegrated due to high production of HEL. In mice with no apparent lenticular changes the inflammation was enhanced by capsulotomy. The inflammation affected all segments of the eye and persisted for at least 39 days after adoptive transfer of cells. Four days after cell injection, the inflammation consisted of subacute infiltration, with both mononuclear and polymorphonuclear leukocytes, whereas more chronic infiltration was seen at later times. Vigorous cellular immunity but no antibody to HEL was found in recipient mice, thus demonstrating the exclusive participation of cellular immunity in the pathogenesis of this experimental disease.
CONCLUSIONS. Transgenic mice expressing HEL in their lenses develop intraocular inflammation after injection of syngeneic lymphocytes sensitized against HEL. This experimental disease is a novel cell-mediated model for LAU.
| Introduction |
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The potential involvement of cellular immunity in the pathogenesis of LAU in humans is unclear, but lymphocyte responses against crystallins were found in patients with cataracts, in particular after extracapsular lens extraction.5 To investigate whether LAU can be mediated by a cellular immune response, we developed a novel experimental system in which transgenic (Tg) mice expressing a foreign antigen, hen egg lysozyme (HEL), in their lens are injected with lymphocytes specifically sensitized against HEL. The lymphocytes are obtained from wild-type (WT) syngeneic mice that are immunized against this foreign antigen. Preliminary observations on this system have been briefly described elsewhere6 ; the present communication reports new data of an extended study in which the following parameters of the experimental system have been examined: detailed analysis of the histologic changes in different lines of Tg mice, after adoptive transfer of various numbers of activated lymphocytes, kinetics of these changes, the effect of capsulotomy on the inflammatory reaction, and the cellular and humoral immune responses in the recipient mice.
| Materials and Methods |
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A-crystallin promoter were generated as described in detail
elsewhere.4
Transgenic mouse lines used here included
those expressing low or high copy numbers of the membrane-bound HEL
(M-HEL) and those expressing the soluble form of the protein
(S-HEL).4
Normal female FVB/N mice, 6 to 8 weeks old,
provided by the National Cancer Institute breeding facility (Frederick,
MD), were used as the syngeneic WT donors of splenocytes. All
procedures with mice were carried out in compliance with the ARVO
Statement for the Use of Animals in Ophthalmic and Vision Research.
Adoptive Transfer of HEL-Sensitized Splenocytes
Donor WT mice were immunized with 50 µg HEL (Sigma, St. Louis,
MO), emulsified with CFA containing Mycobacterium
tuberculosis at 2.5 mg/ml (Difco, Detroit, MI). The emulsion, in a
volume of 0.2 ml, was injected subcutaneously into the base of the tail
and the two hind thighs. Spleen cells of these donors were collected 12
to 14 days postimmunization and stimulated in culture with HEL as
follows: aliquots of 4 x 106 cells were
cultured in 12-well cluster plates in 2 ml RPMI-1640 medium
supplemented with 5% fetal calf serum, 50 µM 2-mercaptoethanol,
antibiotics, and HEL at 10 µg/ml. After incubation for 3 days, the
cells were collected, washed, and injected intraperitoneally into Tg
mice, as indicated. Unless otherwise stated, the recipient mice were
killed 4 days after cell injection. Experimental groups consisted of 2
to 8 animals. The inflammatory changes and the immune responses were
remarkably similar among mice of each group.
Capsulotomy
After deeply anesthetizing the mouse, the eye to be operated on
was first treated topically with a drop of AK-DILATE (Akorn, Abita
Springs, LA). Subsequently, this eye received topically a drop of
Ophthetic 0.5% (Allergan; Hormigueros, Puerto Rico) for additional
anesthesia. After the eye was sufficiently dilated, a 30-gauge needle
was inserted into the anterior chamber through the peripheral third of
the cornea. The lens capsule was then incised in a linear fashion using
the tip of the needle (iris was not punctured). Triple antibiotic
ointment (Phoenix Pharmaceutical, St. Joseph, MO) was applied topically
at the completion of the procedure.
Histologic Examination
Eyes were fixed in 4% glutaraldehyde for 30 minutes before being
transferred to 4% formaldehyde. Sections were prepared and stained
with hematoxylineosin by conventional methods.
Immune Responses of Donor and Recipient Mice
Blood samples and spleens were collected immediately after the
mice were killed and tested for humoral and cellular immunity to HEL,
using the enzyme-linked immunosorbent assay (ELISA) and the lymphocyte
proliferation assay, respectively. The two assays are described
elsewhere.4
| Results |
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Persistence of Ocular Changes in Recipient Mice
Eyes of recipient mice were routinely examined 4 days after cell
injection. Eyes examined after longer periods revealed that the
inflammation persisted for at least 39 days after adoptive transfer of
the cells. An eye section with typical changes at 39 days after cell
injection is shown in Figures 2G
and 2H
. The changes include a
granuloma-like structure with fibroblasts and neovascularization
extending toward the retina, as well as retinal vasculitis, with mainly
MN leukocytes.
Immune Responsiveness to HEL in Recipient Mice
To further elucidate the immunologic capacity of
the adoptively transferred splenocytes in the recipient mice, we tested
these mice for HEL antibodies in their serum and for proliferative
responsiveness against HEL by their spleen lymphocytes. Figures 3
and 4
, respectively, summarize data of representative recipient mice. For
comparison, these figures also record the immune responses of typical
WT mice actively immunized with HEL. High levels of HEL antibodies were
measured in sera of the immunized WT mice, but no antibody could be
detected in sera of recipient mice at any tested time after transfer of
HEL-sensitized splenocytes (Fig. 3)
. In contrast, spleen cells of
recipient mice responded vigorously to HEL, with stimulation indices
similar or even higher than those monitored in cultures of spleen cells
from the actively immunized mice (Fig. 4)
. The high level of cellular
immune response to HEL was retained in recipient mice for at least 39
days after cell injection (Fig. 4)
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| Discussion |
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The ocular inflammatory process was particularly severe in high copy
number M-HEL-Tg recipient mice, in which the lens capsule was
disintegrated and allowed exposure of lens proteins (Fig. 1) . However,
inflammation was also observed in eyes of S-HEL-Tg or low copy number
M-HEL-Tg mice (Figs. 2A
-C), in which no apparent morphologic changes
were seen in the lens.4
The latter finding differs from
observations in the two experimental models of antibody-mediated LAU,
i.e., "experimental lens-induced granulomatous endophthalmitis" and
"Arthus-type panophthalmitis"; in both models inflammation
developed only after puncture of the lens capsule.1
2
Moreover, we have recently found that lymphocytes from
B-crystallin
knockout mice sensitized against murine
B-crystallin induce intense
ocular inflammation when injected into naive WT recipient mice, but
only after capsulotomy; no inflammation was detected in
uncapsulotomized recipient eyes (M. Gelderman et al., unpublished
data). It is proposed, therefore, that despite their normal appearance,
lenses of the S-HEL-Tg and low copy number M-HEL-Tg mice are altered by
the transgenic production of HEL in a manner that makes HEL more
accessible to the immune system than are lens crystallins in a normal
eye.
The relevance of the experimental system described here to clinical LAU is not clear since no direct evidence is available to show involvement of cell-mediated immunity in the pathogenesis of the human disease. Had such involvement been established, the animal disease described here could become a model for the human entity.
The histopathologic changes in eyes of the recipient mice were subacute when examined 4 days after cell injection (Figs. 1C -E) and became more chronic and granulomatous in eyes collected at later time points (Figs. 2G and 2H) . The inflammatory changes induced by sensitized lymphocytes in mice in the present study resemble in certain aspects those seen in rats with experimental LAU, in which the pathogenic processes are antibody-mediated.1 2 Of particular interest is the finding that the cellular infiltration in recipient mice in the present study consisted to a large extent of PMN leukocytes that typically are the hallmark for Arthus-like, antibody-mediated inflammatory reactions. This observation resembles our previous finding,7 that PMN leukocytes are a major component of the cellular infiltration in eyes of rats in which experimental autoimmune uveoretinitis is adoptively transferred by lymphocytes sensitized against retinal antigens. It is assumed that in both systems the initial immunopathogenic process is triggered when small numbers of specifically sensitized lymphocytes recognize their target ocular antigen, become activated, and release a battery of inflammation-promoting cytokines, including chemokines. The PMN leukocyte involvement in lymphocyte-mediated ocular inflammation is attributed to the activity of certain chemokines that selectively attract PMN leukocytes.10 These chemokines are assumed to be produced by the inflammatory cells, as well as by resident ocular cells.10 The finding that similar PMN infiltrations characterize ocular inflammation of various origins suggests that chemokines produced by resident ocular cells play a major role in these disease processes. These notions are currently under investigation.
| Acknowledgements |
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| Footnotes |
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Submitted for publication January 7, 1999; revised June 10, 1999; accepted June 24, 1999.
Commercial relationships policy: N.
Corresponding author: Igal Gery, NEI, NIH, Building 10, Room 10N112, Bethesda, MD 20892-1857. E-mail: igery{at}helix.nih.gov
| References |
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