Investigative Ophthalmology & Visual Science, Vol. 31, No. 7, July 1990
Copyright © Association for Research in Vision and Ophthalmology
Humoral Autoimmune Response Against S-Antigen
and IRBP in Ocular Onchocerciasis
A. Van der Lelij,* G. Doekes,f B. 5. Hwan,f J. C. M. Verrer,^: E. Riefveld,* J. 5. 5rilma,§ and A. Kijlstraf
Autoimmune mechanisms are thought to play a role in the pathogenesis of the chorioretinal changes in
ocular onchocerciasis. In this study the involvement of autoimmunity against retinal antigens in
developing chorioretinitis was investigated. Serum levels of autoantibodies, directed against human
S-antigen and interphotoreceptor retinoid-binding protein (IRBP), were determined in patients with
onchocerciasis (n = 46) and endemic controls (n = 38) from Sierra Leone with the use of an enzyme
immunoassay. In both groups high levels of anti-human S-antigen and IRBP antibodies were detected.
No relationship could be demonstrated between the antiretinal antibody level and the occurrence of
chorioretinitis in onchocerciasis. The levels of both anti-human S-antigen and IRBP antibodies were
significantly higher in patients with onchocerciasis compared with endemic controls (P < 0.001).
Cross-reactivity of antiretinal antibodies with parasitic antigens could not be demonstrated as a
possible explanation for the higher levels in patients with onchocerciasis. No correlation was found
between the levels of antibodies of different classes against the crude Onchocerca volvulus, the egg
antigen, or the microfilariae and the antiretinal antibody levels. Furthermore, in a panel of 13 different
monoclonal antibodies directed against O. volvulus, only one showed a slight anti-human IRBP reactivity and none reacted with S-antigen. The immune response against the two retinal antigens investigated was not specific for onchocerciasis because high antibody levels were also found in patients with
Bancroftian filariasis from Papua, New Guinea, and Surinam. The finding of retinal autoimmunity in a
selected group of people from West Africa could well be explained by the induction of polyclonal B cell
activation resulting from parasitic infection. Circulating antibodies against human S-antigen or human
IRBP are thus not specific for onchocerciasis and are in themselves not sufficient to cause chorioretinopathy in onchocerciasis, although their pathogenic role in an ongoing chorioretinitis cannot be
excluded. Invest Ophthalmol Vis Sci 31:1374-1380, 1990
Ocular onchocerciasis is a major cause of blindness
in Africa and some parts of Central and South America. Up to 85 million people are exposed to the risk of
infection with the nematode Onchocerca volvulus,
which is transmitted byfliesof the Simulium species.
Worldwide, an estimated one million people have
significant visual loss, leading to at least partial disability as a result of onchocerciasis. In most cases this
visual loss results from corneal scarring or pathologic
changes in the retina, choroid, or optic nerve or in a
combination of these.12 Ocular onchocerciasis clinically presents as punctate keratitis, sclerosing keratitis, iridocyclitis (with or without secondary
From the Department of Ophthalmology,* Free University,
Amsterdam; The Netherlands Ophthalmic Research Institute,f
Amsterdam; the Department of Medical Microbiology,:): University of Amsterdam, Amsterdam; and F. C. Donders Institute of
Ophthalmology,§ Utrecht, The Netherlands.
Submitted for publication: May 30, 1989; accepted November
27, 1989.
Reprint requests: A. Van der Lelij, MD, The Netherlands Ophthalmic Research Institute, P.O. Box 12141 1100 AC Amsterdam
ZO, The Netherlands.
1374
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glaucoma), degenerative chorioretinitis, and optic
atrophy.
The punctate keratitis develops as an inflammatory reaction to dead microfilariae. Histologic examination of these lesions shows necrotic parasites in the
corneal stroma, surrounded by lymphocytes and eosinophils.3 However, little is known about the natural
history of the chorioretinitis.1'45 Although living microfilariae have been detected in the retina in vivo6
and demonstrated histologically in retinal tissue,7 the
evidence of onchocerciasis as an etiologic factor remains largely epidemiologic.
One explanation may be that initially the disease
process starts with a choroiditis and is followed by a
secondary degeneration of the overlying pigment epithelium and neuroretina, in which the atrophic lesion
is possibly an end stage. This hypothesis is supported
by experimental studies in the rabbit.3 In this experimental model the extent of the atrophy is often disproportionate to the histologic evidence of uveitis.
This suggests that other factors, besides an inflammatory reaction to in situ microfilariae, are involved.
Numerous hypotheses have been put forward con-
1375
RETINAL ANTIBODIES IN ONCHOCERCIASIS / Von der Lelij er ol
No. 7
cerning the pathogenesis of the chorioretinopathy.
Autoimmunity is one of the factors that are thought
to play a role in the subsequent events leading to
atrophy of the pigment epithelium and choriocapillaris. New data appear to confirm the hypothesis of
an autoimmune pathogenesis. Antibodies against bovine retinal S-antigen have been detected in patient
sera with the aid of an enzyme-linked immunosorbent assay technique (ELISA) and a human basophil
degranulation test (HBDT).8 We have extended these
experiments by investigating the antibody response
against two well-defined retinal proteins, S-antigen
and interphotoreceptor retinoid-binding protein
(IRBP). The uveitogenicity of these proteins has been
demonstrated in a variety of animal species, including primates.9 In the study presented here we used
antigens isolated from human retinas in view of the
difference in antigenicity between human and bovine
retinal proteins.1011
Materials and Methods
Patients and Controls
In 1985 and 1986 blood was obtained from patients with onchocerciasis (n = 46) and from endemic
controls (n = 38) in Sierra Leone, West Africa. These
two groups were subdivided on the basis of the skinsnip test results and the reaction within 24 hr after
ingestion of a test dose of 50 mg diethylcarbamazine
(Mazzotti test). People with positive skin-snip test results or positive Mazzotti test results were considered
to have onchocerciasis. People with negative skin
snip-test results and negative Mazzotti test results
were accepted as endemic controls.
None of the patients was being treated with diethylcarbamazine (DEC), suramin, or corticosteroids at
the time a blood sample was drawn, although some of
them had been treated with these drugs in the past.
The two groups were examined according to the Onchocerciasis Survey Form.12 A summary of their ocular status is shown in Table 1. A number of symptoms
were not visible because of opacities in the anterior
segment. Chorioretinitis was scored in case of early
disruption of retinal pigment alone or with exposure
of the choroid and clumping of retinal pigment at any
degree. Venous blood (10 ml) was drawn from each
person. Frozen serum was transported to the Netherlands in iceboxes. There were three other control
groups in addition to the endemic controls from
Sierra Leone. Two groups consisted of patients with a
Bancroftian filariasis from Papua, New Guinea (n
= 22), and Surinam (South America) (n = 28). Their
serum was collected in 1987 and kept frozen at
-20°C until use. A third control group consisted of
healthy Dutch people (n = 25). Informed consent of
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Table 1. Ophthalmologic features in onchocerciasis
patients and endemic controls from Sierra Leone
Endemic
controls']
(7i = 38)
Onchocerciasis
patients*
(n = 46)
Ocular status
OD
OS
OD
OS
Visual acuity (<6/60)
IOP (>22 mmHg)
MF/cornea
MF/AC
Snowflake keratitis
Sclerosing keratitis
Iritis
Lens cataract:
Early
Advanced
Mature
Posterior segment changes
Retina/choroid
Optic nerve (except
cupping)
Optic nerve/cupping
13/46
8/46
6/45
14/43
20/43
6/43
8/41
15/46
9/46
9/46
18/46
20/46
8/46
11/45
1/38
2/38
0/38
0/38
0/38
0/38
0/38
1/38
2/38
0/38
0/38
0/38
0/38
0/38
6/39
1/39
1/39
7/42
2/42
1/42
0/38
0/38
1/38
1/38
0/38
0/38
6/36
10/40
0/38
0/38
7/39
5/39
6/39
5/39
0/38
1/38
0/38
1/38
* Age (yr): mean, 36.6; range 18-70.
t Age (yr): mean, 30.5; range 11-60.
Data represent number of affected eyes over total eyes evaluated. In a
number of cases symptoms were not visible, because of opacities in the
anterior segment.
IOP, intraocular pressure; MF, microfilaria; AC, anterior chamber.
patients and controls was obtained after the study was
explained.
Monoclonal Antibodies Against O. volvulus
The procedure for isolating the cuticle and the internal organs such as intestine and uterus from the
adult worms was as follows. Adult worms, derived
from a nodule of an patient with onchocerciasis from
Sierra Leone, underwent a microdissection to separate the cuticle and the internal organs.13 A modification was introduced for separating the eggs from the
microfilariae by means of filtration over planktongauze with a pore size of 15 urn.
Monoclonal antibodies (mAbs) were produced,
with the use of the method developed by Kohler and
Milstein.14 Eight mAb preparations were directed
against the surface of the egg of the O. volvulus and
another five mAbs against the epicuticle of the adult
parasite. In this article the mAbs used were mouse
ascites fluid, in a final dilution of 1/20.
A mouse I g d monoclonal PDS1, directed against
porcine S-antigen (kindly provided by Dr. J. P.
Banga, London, England), was used as a positive
control on the reagents in the anti-human S-antigen
ELISA (see below). In the anti-human IRBP ELISA,
we took a rabbit anti-human IRBP antiserum diluted
1/1000 in phosphate-buffered saline (PBS)-Tween
20® (OPG Farma, Utrecht, The Netherlands) as a
positive control.
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INVESTIGATIVE OPHTHALMOLOGY 6 VISUAL SCIENCE / July 1990
Human S-Antigen and Human IRBP
Human S-antigen and human IRBP were isolated
from retinas of human cadaver eyes from which the
corneas had been removed for transplantation. These
retinas were stored at —20°C until use.
The isolation of human S-antigen was performed
as described by Doekes et al.15 A 50% ammonium
sulfate precipitation of retinal extract was followed by
DEAE (DE-52, Whatman Corporation, Kent, United
Kingdom) anion exchange chromatography and gel
nitration.
Human IRBP was purified with the use of a modification of the method described by Adler et al.1617
After thawing, the retinas were extracted with cold
PBS containing 0.1 mM phenylmethyl-sulfonyl fluoride (PMSF; Sigma, St. Louis, MO) and 0.02% NaN3,
pH 7.4, for 1 hr at 4°C. After centrifugation for 30
min at 3,000 g, the pellet was resuspended in the
same solution and the extraction procedure was repeated. Both supernatants were collected and concentrated by ultrafiltration on an XM-50 Diaflo®
ultrafiltration membrane (Amicon Corporation,
Danvers, MA). Further isolation was performed by
30% ammonium sulfate precipitation and affinity
chromatography on a Concanavalin A-Sepharose®
column (Pharmacia AB, Uppsala, Sweden) in PBS,
containing 0.5 M NaCl, 0.2 mM PMSF, and 0.02%
(w/v) NaN3, (pH 7.4). Human IRBP was eluted with
2.0 M methyl «-D glucopyranoside (Sigma) in the
same buffer. Finally, gel filtration on a SephacrylS300® column (Pharmacia AB, Uppsala, Sweden)
was performed in the same buffer as that used for the
Concanavalin A-Sepharose® column, with the addition of 0.1% (v/v) Tween 20®. At every step of the
isolation procedure, the purity and the molecular
weight of human IRBP was assessed by electroforesis
on polyacrylamide gels in sodium dodecyl sulfate
(SDS-PAGE) and an ELISA with the use of a rabbit
antibovine IRBP antiserum (kindly provided by Dr.
R. M. Broekhuyse, Nijmegen, The Netherlands).
Protein concentrations were determined with the
Bradford method, using bovine serum albumin as a
standard.18 The homogeneity and the identity of
human S-antigen and human IRBP were confirmed
by SDS-PAGE using samples of about 10 /zg each,
with Coomassie Brilliant Blue (Merck-Schuchardt,
Darmstadt, Federal Republic of Germany) staining
of the gels. Both proteins showed one band on the
gels. The molecular weights were 50 kD and 135 kD,
respectively.
Enzyme-Linked Immunosorbent Assay
An ELISA was used to detect antibodies against
human S-antigen and human IRBP. The procedure
was performed as described by Doekes et al15 with
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Vol. 31
some modifications. Microtiter plate wells (Greiner,
product no. 655101, Alphen aan de Rijn, The Netherlands) were coated with 100 ng human S-antigen or
human IRBP in 0.1 ml 0.05 M carbonate/bicarbonate buffer (pH 9.6), containing 0.02% (w/v) NaN3 for
1 hr at room temperature. After they were washed
three times with PBS containing 0.1% (v/v) Tween
20® (PBS-Tween®) the wells were incubated with
0.1 ml serum diluted 1/20 in PBS-Tween®. All sera
were tested in coated and uncoated wells as a control
for a specific binding. After 1 hr at room temperature,
the plates were washed and 0.1 ml rabbit anti-human
IgG, IgM, IgA, kappa, lambda antiserum conjugated
with horseradish peroxidase (DAKOPATTS, Copenhagen, Denmark) diluted 1/500 in PBS-Tween® was
added. After incubation for 1 hr at room temperature
and three washes with PBS-Tween®, the plates were
incubated for 30 min at room temperature with 0.1
ml 0.20 mM ABTS (Boehringer, Mannheim, Federal
Republic of Germany) in 0.05 M citric acid (pH 4.0)
containing 0.15% H2O2. The green reaction product
was measured in a spectrophotometer at 405 nm.
To detect antibodies of the IgE class against human
S-antigen and IRBP, a rabbit anti-human IgE antiserum conjugated with horseradish peroxidase (Nordic, Tilburg, The Netherlands) was used instead of
rabbit anti-human Ig-PO in the same dilution.
In each plate at least five coated and five uncoated
wells were incubated with PBS-Tween instead of
serum, to correct for the amount of rabbit antihuman Ig-PO or rabbit anti-human IgE-PO directed
against human S-antigen or human IRBP.
Calculations were made as follows:
in which
Aa,t = mean Extinction at 405 nm in S-antigen or
IRBP coated wells incubated with test
serum;
A ct = mean E 405 nm in uncoated wells incubated
with the same test serum;
A ao = mean E 405 nm in S-antigen or IRBP coated
wells incubated with PBS-Tween®;
Aco = mean E 405 nm in uncoated wells incubated
with PBS-Tween®.
The expression (Aa,o - A co ) in the formula was
0.009 ± 0.006 for human S-antigen and 0.105
±0.019 for human IRBP.
In the anti-human S-antigen ELISA a reference
serum was always included as a positive control. This
serum, from a healthy Dutch person, contained a
relatively high level of antibodies directed against
human S-antigen.15
The possibility of an amplification of the ELISA
system by rheumatoid factor in the tested sera was
also investigated. A serum, which contained a high
RETINAL ANTIBODIES IN ONCHOCERCIASIS / Von der Lelij er ol
No. 7
level of rheumatoid factor of the IgM class, was added
to the reference serum in the anti-human S-antigen
ELISA in a dilution with a moderate extinction. No
elevation of the original extinction was observed,
which meant that interference of rheumatoid factor
in our assay system was not likely. The reference
serum itself did not contain rheumatoid factor.
In the anti-human IRBP ELISA, only a rabbit
anti-human IRBP antiserum was used as a positive
control because no patients or healthy Dutch people
were found to have significant amounts of antihuman IRBP antibodies.
A serum was considered negative if the corrected
extinction was lower than 0.100.
The statistical analysis of data was performed with
the use of the Mann-Whitney rank-sum test.
Results
The role of autoimmunity against retinal proteins
in onchocerciasis was investigated by measuring antibodies against human S-antigen and human IRBP in
serum. High levels of anti-human S-antigen antibodies were detected in all sera of patients with onchocerciasis and in endemic controls from Sierra Leone
(Fig. 1). In both groups a considerable range of values
was recorded. The level of anti-human S-antigen antibodies in patients with onchocerciasis (mean: 0.462)
was significantly higher than in the endemic controls
(mean: 0.336; Mann-Whitney rank-sum test; P
< 0.001). In the control group made up of healthy
Dutch people, in 32% an extinction of more than
0.100 was recorded, but the mean value (0.084) of
anti-human S-antigen antibody activity was much
lower than in the groups from Sierra Leone.
To ascertain whether the level of anti-S-antigen an-
0.1
0.0
onchocerciasis
endemic
controls
Sierra Leone
New Guinea Surinam
Netherlands
Fig. 1. Circulating antibodies against human S-antigen in onchocerciasis patients and endemic controls from Sierra Leone; patients with Bancroftian filariasis from Papua, New Guinea, and
Surinam; and healthy controls from the Netherlands.
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1377
Fig. 2. Anti-human S-antigen and anti-human IRBP antibodies
in onchocerciasis in relation with chorioretinitis. Results show the
mean and standard deviation.
tibodies was related to posterior segment involvement, we divided the onchocerciasis group into patients with and without chorioretinitis. Of the 46 patients, 10 had clear-cut evidence of chorioretinal
changes in one or both eyes (Table 1). The fundus in
ten right eyes and six left eyes could not be examined
because of anterior segment opacities, whereby both
eyes were involved in five patients. Eyes with opaque
media were considered to be chorioretinitis negative.
There was no difference between the anti-human Santigen levels in patients with and those without chorioretinitis (Fig. 2), nor could a correlation be demonstrated between the anti-human S-antigen antibodies
and the number of microfilariae in the cornea, anterior chamber, or skin-snip (data not shown).
To determine whether the presence of high serum
levels of anti S-antigen in onchocerciasis resulted
from cross-reaction of retinal S-antigen with parasitic
antigens, the following experiments were performed.
All sera of patients with onchocerciasis were tested
for separate IgG, IgM, IgA, and IgE antibodies against
the crude O. volvulus, the egg antigen, and microfilariae. No correlation could be demonstrated between the levels of the antibodies mentioned above
and the concentration of antibodies against human
S-antigen (data not shown).
Cross-reactivity between the parasite and human
S-antigen was also studied in the following manner.
Thirteen different mAbs directed against the egg surface or the epicuticle of the adult O. volvulus were
tested for anti-human S-antigen activity. None of
these mAbs reacted with human S-antigen (Fig. 3).
As we have seen, the levels of anti-human S-antigen were higher in patients with onchocerciasis than
in the endemic controls (Fig. 1). To investigate
whether this may be seen as a phenomenon specific
to onchocerciasis or as a general finding in filarial
diseases, we tested two groups of patients with Bancroftian filariasis, a disease without the ocular symp-
INVESTIGATIVE OPHTHALMOLOGY b VISUAL SCIENCE / July 1990
1378
Vol. 31
i.u 0.90.80.7•
0.60.50.40.30.20.1 -
:
0.0-
••-?•—
1
mAb
PDS1
0.4
mAb
0.6
RaHulRBP
anti-human S-antigen
anti-human S-antigen
anti-human IRBP
Fig. 3. Reactivity of monoclonal antibodies directed against Onchocerca volvulus with human S-antigen and IRBP. A mouse antiporcine S-antigen monoclonal antibody (PDS1) and a rabbit antihuman IRBP antiserum (RaHulRBP) were taken as positive controls.
toms seen in onchocerciasis. The sera of patients
from Papua, New Guinea, with Bancroftian filariasis
also showed high levels of antibodies directed against
human S-antigen; all sera had detectable levels and
the mean extinction was 0.359. Patients from Surinam with Bancroftian filariasis, however, had a much
lower level of anti-human S-antigen antibodies; only
21% of the sera had an extinction of more than 0.100
and the mean was 0.091.
When tested for human IRBP autoantibodies, the
five groups (patients with onchocerciasis, endemic
controls, two groups of patients with Bancroftian filariasis, and healthy Dutch controls) showed a pattern
similar to that of human S-antigen (Fig. 4). There
Fig. 5. Relationship between anti-human S-antigen and antihuman IRBP antibodies in sera from Sierra Leone. Data are represented as the corrected extinctions at 405 nm.
were a few exceptions. In the onchocerciasis group
2% and in the endemic control group 8% had subdetectable levels of antibodies against human IRBP.
Furthermore, the anti-human IRBP antibody levels
in the group of patients from Papua, New Guinea,
with Bancroftian filariasis (mean: 0.555) were significantly higher than those of the patients with onchocerciasis (Mann-Whitney rank-sum test; P < 0.05).
As with S-antigen, no relation could be demonstrated
between the levels of anti-human IRBP antibodies
and the occurrence of chorioretinitis (Fig. 2). No relationship could be demonstrated between the antiIRBP antibodies on one side and antibodies directed
against the crude O. volvulus, the egg-antigen or the
microfilariae (whether it concerned IgG, IgM, IgA,
IgE antibodies) on the other side. One of the 13 m Abs
raised against parasitic antigens showed a slight antihuman IRBP activity (Fig. 3). This was an mAb directed to the surface of the egg of the parasite.
In people from Sierra Leone (both patients with
onchocerciasis and endemic controls) there was a
correlation between the anti-human S-antigen and
anti-human IRBP reactivity (Fig. 5; Mann-Whitney
rank-sum test; P < 0.001).
Discussion
onchocerciasis
|
Sierra Leone
healthy
controls
| [New Guinea) [ Surinam | | Netherlands
bancroftian filariasis
|
Fig. 4. Circulating antibodies against human IRBP in onchocerciasis patients and endemic controls from Sierra Leone; patients
with Bancroftianfilariasisfrom Papua, New Guinea, and Surinam;
and healthy controls from the Netherlands.
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In the experiments described in this article, autoantibodies against human S-antigen and human IRBP
were detected in all patients with onchocerciasis and
in nearly all the endemic controls. We found no relationship between the levels of antibodies against these
retinal proteins and the occurrence of chorioretinitis.
These findings indicate that autoimmune reactions
against S-antigen and IRBP are not pathognomonic
for chorioretinopathy in onchocerciasis. Furthermore, no link was observed between the anti-human
No. 7
RETINAL ANTIBODIES IN ONCHOCERCIASIS / Van der Lelij er al
S-antigen or IRBP antibodies and any ophthalmologic feature of the patients with onchocerciasis.
In this study antibody levels were measured with
the use of an ELISA system, whereby the autoantibodies were detected with a peroxidase-conjugated
second antibody recognizing the public determinants
of the human immunoglobulins. Although variable
ratios of different classes of autoantibodies and antibody avidities may have influenced the ELISA reactivity, implicating a poor correlation between ELISA
readings and actual autoantibody levels, this method
is at present the best quantitative procedure to analyze large series of patient sera.
Autoimmunity against ocular antigens has often
been suggested as a possible etiologic factor in the
pathogenesis of chorioretinopathy. Evidence for this
hypothesis was obtained by Vingtain et al,8 who investigated the humoral immune response against bovine S-antigen and human retinal extract in onchocerciasis. Autoantibodies against both antigen preparations were found in 11% of patients without retinal
involvement, whereas 40% of patients with chorioretinitis had positive results. No difference was found,
however, when comparing bovine S-antigen antibody
levels between patients with or without chorioretinal
involvement, which is in agreement with our findings.
In a later study performed in a larger group of patients, however, the same authors19 reported a significantly higher level of S-antigen autoantibodies in patients with posterior pole involvement.
Chan et al20 also demonstrated circulating antibodies against retinal constituents in onchocerciasis using
an indirect histochemical immunoperoxidase technique. Of interest was the observation that these autoantibodies could not be absorbed with S-antigen or
IRBP, suggesting that other retinal antigens were involved. It is not clear, however, whether the technique used was adequate to pick up circulating antiS-antigen or IRBP antibodies.21 Furthermore, it was
not clear whether the absorptions were performed
with bovine or human retinal antigens, which may
help to explain the negative absorption studies.
Unlike Vingtain et al,8 we were not able to detect
IgE antibodies against S-antigen in patients with onchocerciasis (data not shown). This was an important
observation because in experimental autoimmune
uveoretinitis (EAU) induced by bovine S-antigen
there is evidence of an IgE-mediated mechanism.22
The occurrence of antiretinal antibodies in onchocerciasis may be explained by cross-reactivity of these
antibodies with parasitic antigens. We could not
demonstrate this because various mAbs against egg
antigen or epicuticle antigen of the parasite did not
react with human S-antigen or human IRPB (Fig. 4).
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1379
Moreover, there was no correlation between antibody
levels to different stages of parasites or organs of parasites and antiretinal antibody levels. These observations of course do not exclude a possible cross-reactivity. Additional experiments using specifically purified antibodies in various absorption or inhibition
studies should be performed to ultimately answer this
question.
The finding of retinal autoimmunity in a selected
group of people from West Africa could well be explained by the induction of polyclonal B cell activation as a result of parasitic infection. Earlier studies
from our group showed that the investigated population from Sierra Leone was infected with at least one
to four other parasites23 and that most people had
significantly elevated levels of immunoglobulins
compared with Dutch normal donors.24 Moreover,
malaria and trypanosomiasis are endemic in Sierra
Leone. In the latter two infections a role for polyclonal B cell activation was clearly demonstrated.25'26
The finding that patients from Surinam and Papua,
New Guinea, with Bancroftian filariasis had high
levels of antiretinal antibodies is in agreement with
the fact that three and, in the latter, four of the mentioned nononchocercal parasitic infections were also
endemic in these areas. This explanation of polyclonal activation is supported by the fact that several
kinds of autoantibodies have already been demonstrated in patients with onchocerciasis and in endemic control groups.527 Although the presence of
rheumatoid factor (RF) in these sera could have influenced our results, we did not observe an amplification of the signal in the ELISA by adding IgM-RF
to our system.
Our conclusion, that antibodies against human Santigen and human IRBP are not specific for onchocerciasis and are in themselves not sufficient to cause
the chorioretinopathy in this disease on the long
term, is supported by the observation that EAU could
not be induced by passive transfer of antiretinal antibodies.28 A possible role of antibodies in EAU was
indicated by the presence of histologic changes typical of local antigen-antibody reactions and by experiments whereby depletion of complement resulted in
a reduced intensity of the disease in guinea pigs.9'29
Taken together, these findings suggest that autoantibodies against retinal constituents play an additional
role in this primary T-cell-mediated uveitis model.
Future studies should be devoted to the question of
whether cellular immune reactions against retinal
antigens are involved in the chorioretinopathy in onchocerciasis.
Key words: ocular onchocerciasis, chorioretinopathy, autoimmunity, S-antigen, IRBP
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INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / July 1990
Acknowledgments
The authors thank Prof. Dr. H. J. M. Weve Stichting for
providing the necessary funds that made it possible to do
thefieldworkin Sierra Leone. The authors also thank C. A.
Lips for her help in preparing the manuscript.
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