|
|
||||||||
1 From the Department of Ophthalmology and Neuroscience Program, the W. K. Kellogg Eye Center, University of Michigan, Ann Arbor; and the 2 Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA.
| Abstract |
|---|
|
|
|---|
METHODS. MAR IgG was isolated from three visually symptomatic melanoma patients. Control IgG was from melanoma patients with no vision problems. The ERG was monitored after intravitreal injections into monkey eyes. One eye was injected with 2-amino-4-phosphonobutyric acid (APB), which is known to block DBC ON-pathway responses. Retinal immunocytochemistry was performed using fluorescein isothiocyanatelabeled goat anti-human IgG.
RESULTS. Within 1 to 3 hours after MAR IgG injection, the ERG photopic b-wave was diminished, with far less effect on the a- and d-waves. These changes are characteristic of DBC dysfunction and were similar to the effects of APB. The scotopic ERG b-wave, which reflects activity of rod-driven DBCs, showed a loss of amplitude and threshold sensitivity after MAR IgG. Retinal immunocytochemistry with anti-IgG antibody showed IgG penetration throughout the retinal layers, but staining was not specific for a single type of retinal neuron.
CONCLUSIONS. Intravitreal injection of human MAR IgG altered the monkey ERG acutely in ways that implicate functional disruption of retinal DBC signaling. These results support the hypothesis that MAR IgG circulating antibodies are responsible for the reported visual symptoms. Bipolar cells in the ON-pathway appear to be affected more than OFF-pathway bipolar cells of the cone pathway in this acute preparation.
| Introduction |
|---|
|
|
|---|
In addition to MAR, cancer-associated retinopathy (CAR) also produces vision symptoms.6 7 8 Serum antibodies in MAR and CAR are reactive against retinal cells and proteins,2 7 8 suggesting an autoimmune basis for both conditions. The proposed mechanism involves a B-lymphocyte response against tumor cell antigens, resulting in autoantibodies that cross-react with retinal cellular antigens. MAR antibodies bind to bipolar cells and their dendrites in the outer plexiform layer of human retinal sections.2 CAR antibodies react with recoverin, a 23-kDa calcium-binding protein found in photoreceptors and some types of cone bipolar cells.7 8 This presumed mechanism of autoimmune disease is also known for the hearing disorders, in which some paraneoplastic inner ear diseases cause sensory neural hearing loss.9 Treatment by immunosuppression can sometimes partially rescue the vision or hearing deficit, this is a further indication of immune system involvement in the sensory component of these conditions.6 10
In the case of CAR, intravitreal injection of anti-recoverin antibodies induces death of recoverin-positive rat photoreceptor and bipolar cells in vitro11 and in vivo.12 We used this experimental approach and gave MAR IgG by intravitreal injection in monkey eyes to explore whether this could produce an acute functional change in the ERG. We found that within 3 hours after MAR IgG injection the ERG waveform changed in a way that roughly mimicked that reported for MAR patients. The ERG changes in monkey were characteristic of deficient signaling by depolarizing (ON-) bipolar cells and could be simulated by application of the glutamate agonist 2-amino-4-phosphonobutyric acid (APB), which blocks signal transmission to DBCs.13 This demonstrates that MAR antibodies can affect the function of retinal DBCs relatively acutely and provides additional evidence for an autoimmune etiology for MAR disease.
| Materials and Methods |
|---|
|
|
|---|
MAR IgG was from visually symptomatic MAR patients and prepared by column fractionation.2 We had only a limited number of monkey eyes available for study, consequently we pooled MAR sera from three visually symptomatic patients to enhance the possibility of seeing an ERG effect. All three patients had experienced photopsias and night-blindness and had ERG changes. The IgG serum fraction from all three MAR patients had given strong bipolar labeling by immunocytochemistry. Two of these MAR subjects were previously described.3 14
The appropriate dose for MAR IgG was not known, and we used the same concentration of IgG sera, undiluted, as in the previous study2 and injected 0.1 ml volume. The dark-adapted ERG was monitored for indications of a sensitivity change. If none was observed after about 1 hour, a second injection was given, while maintaining dark-adaptation. Elapsed time given in the results for observing ERG changes is after the second injection. Intravitreal injections were made through the pars plana with a 30-gauge needle. Injection of 0.1 ml does not itself alter the ERG,4 and we reconfirmed this in several of these eyes (Table 1) . None of these injections caused retinal hemorrhage or lens damage.
|
One eye (monkey 4) received a 0.1 ml injection of 32 mM APB (Sigma Chemical, St. Louis, MO) solution prepared in phosphate-buffered saline (PBS), with the pH adjusted to 7.3 to 7.4 with NaOH, to demonstrate the expected ERG waveform change associated with blocking light-evoked responses of DBCs under long-flash photopic conditions.4
Retinal immunocytochemistry was performed on the eyes of one animal euthanatized 2 hours after the ERG recording. After removal, eyes were slit at the pars plana and fixed in 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) for 6 hours at 4°C. The anterior segments were removed, and the eyecups were placed in 10% phosphate-buffered sucrose at 4°C. Retinas were cryoprotected in sucrose and cryosectioned at 12 µm thickness. Sections were incubated for 1 hour at room temperature in secondary antibody (goat anti-human IgG labeled with fluorescein isothiocyanate [FITC] at 1:50 in PBS with 0.3% Triton X-100), rinsed twice with PBS for 30 minutes at room temperature, and placed on coverslips in 90% glycerol in PBS containing 2% 1,4-diazabicyclo(2,2,2) octane. The sections were photographed with a Nikon microscope (Tokyo, Japan) equipped for epifluorescence.
| Results |
|---|
|
|
|---|
|
|
MAR IgG also affected the scotopic b-wave (Fig. 3) . The scotopic b-wave derives directly or indirectly from activity of DBCs in the rod pathway.5 The b-wave suppression was quantitatively greater than that caused by the control non-MAR IgG sera (Fig. 3B) . For criterion responses of 50 µV, MAR IgG caused a 1.8 log unit sensitivity loss compared with only 0.6 log unit loss for control sera. We removed these eyes for immunohistochemistry and did not track the ERG changes over a longer period. However, in the two other animals, the MAR IgG effect was reversible with time. As shown in Figure 4 (monkey 3, Table 1 ), MAR IgG acutely caused a 1.2 log unit sensitivity loss of the b-wave (50 µV criterion), and this recovered to within 0.2 log units of baseline when retested at 4 months. The photopic b-wave also recovered in this animal. This recovery suggests that the MAR IgG did not permanently damage retinal neuronal function. We did not study interim time points and do not have a more precise estimation of the recovery time course.
|
|
| Discussion |
|---|
|
|
|---|
MAR IgG altered the ERG of all three monkeys in similar fashion but to a different extent. It is not surprising that intravitreal injection of a mixture of complex proteins might yield differences in waveforms in different animals. We have previously noted differences in photopic ERG waveforms even after applying glutamate analogs (e.g., see waveforms after APB4 15 16 ). Furthermore, even though all 20 human MAR patients reported to date have night-blindness and photopsias, they show different degrees of ERG alteration.1 2 3 Some MAR patients are reported to show only partial b-wave reduction in early disease stages and initially have ERG asymmetry between the two eyes that later evolves to severe bilateral ERG involvement over the course of several weeks (Kenneth Alexander, personal communication; see also the patient course reported in Ref. 2) . In MAR patients circulating antibodies would present chronically to the retina. By comparison, our experimental monkey manipulation provided only a single acute application, which may explain why we did not observe a fully electronegative scotopic response as has been reported for some patients. The consistency of the MAR IgG effect on the photopic ERG in producing an electronegative a-/b-wave complex in two of three monkeys (Fig. 2 , animals 1 and 3) seems remarkable in this context. The effect of MAR IgG on the photopic b-wave was quite evident in the waveform when the OFF-response was separated using the long-flash ERG. In all cases, however, both the rod and cone systems showed a deficit of the ON-pathway ERG attributable to an effect on DBCs. These findings provide further evidence of an autoimmune basis for the visual symptoms experienced by MAR patients.
In an effort to find an alternative non-primate animal model in which to test these ideas further, we conducted a limited set of experiments with MAR IgG in the rod-dominated rat and in the guinea pig, which has a usable photopic ERG. The human MAR IgG decreased the scotopic and photopic ERG responses nonselectively and to a degree similar to that of control serum from normal subjects without melanoma. These studies provided no basis for further experiments with human MAR IgG in these species.
Intravitreal injection of APB produced results that were similar to the MAR IgG effect on the ERG. Although APB specifically targets the mGluR6 receptor on DBCs,17 18 this does not necessarily mean that MAR IgG targets this receptor, because bipolar cell function could also be impaired at the level of a membrane channel or at other sites. Also, the immunostaining pattern of human retinal sections with MAR patient serum showed binding to the bipolar cell soma and was not limited to the synaptic region where mGluR6 receptors are located.2 The retinal antigen recognized by human MAR antibody may be a 33-kDa protein,19 and further information about the specific bipolar cell component that is involved will become clearer once this subcellular target is identified.
| Acknowledgements |
|---|
| Footnotes |
|---|
Submitted for publication March 10, 1999; revised July 8, 1999; accepted August 2, 1999.
Commercial relationships policy: N.
Corresponding author: Paul A. Sieving, Retinal and Macular Dystrophy Center, W. K. Kellogg Eye Center, University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105. psieving{at}umich.edu
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
P. Heiduschka, H. Fietz, S. Hofmeister, S. Schultheiss, A. F. Mack, S. Peters, F. Ziemssen, B. Niggemann, S. Julien, K. U. Bartz-Schmidt, et al. Penetration of Bevacizumab through the Retina after Intravitreal Injection in the Monkey Invest. Ophthalmol. Vis. Sci., June 1, 2007; 48(6): 2814 - 2823. [Abstract] [Full Text] [PDF] |
||||
![]() |
A G Robson, E C Richardson, A H C Koh, C E Pavesio, P G Hykin, A Calcagni, E M Graham, and G E Holder Unilateral electronegative ERG of non-vascular aetiology Br. J. Ophthalmol., December 1, 2005; 89(12): 1620 - 1626. [Abstract] [Full Text] [PDF] |
||||
![]() |
G E Holder, A G Robson, C Pavesio, and E M Graham Electrophysiological characterisation and monitoring in the management of birdshot chorioretinopathy Br. J. Ophthalmol., June 1, 2005; 89(6): 709 - 718. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. R. Alexander, C. S. Barnes, G. A. Fishman, J. Pokorny, and V. C. Smith Contrast-Processing Deficits in Melanoma-Associated Retinopathy Invest. Ophthalmol. Vis. Sci., January 1, 2004; 45(1): 305 - 310. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. M. Palmowski, A. H. Haus, C. Pfohler, U. Reinhold, R. Allgayer, W. Tilgen, K. W. Ruprecht, and C. E. Thirkill Bilateral Multifocal Chorioretinopathy in a Woman With Cutaneous Malignant Melanoma Arch Ophthalmol, December 1, 2002; 120(12): 1756 - 1761. [Full Text] [PDF] |
||||
![]() |
K. R. Alexander, C. S. Barnes, G. A. Fishman, and A. H. Milam Nature of the Cone ON-Pathway Dysfunction in Melanoma-Associated Retinopathy Invest. Ophthalmol. Vis. Sci., April 1, 2002; 43(4): 1189 - 1197. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. J. Hooks, M. O. M. Tso, and B. Detrick Retinopathies Associated with Antiretinal Antibodies Clin. Vaccine Immunol., September 1, 2001; 8(5): 853 - 858. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |