The ocular humoral immune response in health and disease

This review focuses on several aspects of humoral immunologic defence of the ocular surface and intraocular compartment. Secretory IgA (sIgA) is a major component of lacrimal fluid and contributes to the first line of defence against infection of the ocular surface. Recent findings show that part of the lacrimal gland (LG) IgA repertoire consists of so-called natural IgA antibodies. How B cells responsible for these natural IgA antibodies are distributed to effector mucosal sites like the LG is not known. Extensive data are now available on the regionalization of mucosal IgA responses in murine gut, involving peritoneal B cells, the prototypic natural antibody producing cells. By comparing elaborate experiments done in mice with the much less extensive data on the LG, it becomes clear that this gland is a unique, but poorly investigated effector organ of the mucosal immune system. In addition to the humoral immune response at the surface of the eye, the production of antibodies within the ocular compartment also has several fascinating features. The detection of pathogen-specific antibodies in intraocular fluid (IOF) of uveitis patients is accepted as a diagnostic tool, but the specificity of these intraocular antibodies was not investigated in much detail. Recent data however, demonstrate that even antibodies recognizing the same antigen in both serum and IOF still differ in the epitopes they recognize. This reveals that the intraocular compartment largely determines its own antibody profile in the defence against intra-ocular pathogens. Several models as to how an exclusive intra-ocular B cell repertoire may be generated are presented.

The risk and natural course of age-related maculopathy: follow-up at 6 1/2 years in the Rotterdam study

OBJECTIVES

To evaluate the natural course of age-related maculopathy (ARM) and to assess the incidence and absolute risk of its final stage, age-related macular degeneration (AMD).

METHODS

In a population-based prospective cohort study of 6418 persons 55 years and older, we studied the incidence and natural course of ARM. Subjects underwent identical examinations, including stereoscopic fundus photography, at baseline and at 2.0 and 6(1/2) years' follow-up. Age-related maculopathy was graded according to the International Classification and Grading System for ARM and AMD, and stratified into 5 exclusive stages. Incidence was expressed in rates and 5-year absolute risks.

RESULTS

At follow-up, 47 new cases of AMD were identified, with a ratio of neovascular-atrophic AMD of 1.4:1. The 5-year risk of AMD increased with more severe stages to 28.0% for subjects 55 years and older with indistinct drusen and pigmentary irregularities (stage 3). Age, but not sex, independently increased this risk to a maximum of 42.0% for subjects with stage 3 ARM who were 80 years and older. Individual ARM fundus signs that predicted best the development of AMD were 10 or more large drusen (> or =125 microm) and 10% or more of the grid area covered by drusen. Subjects who developed atrophic AMD showed no significant (P =.25) differences in baseline fundus signs and natural course compared with subjects who developed neovascular AMD.

CONCLUSIONS

We provided the absolute risk of AMD as a function of age and early ARM fundus signs, and showed that both are prominent independent risk factors. The progression of ARM stages follows, after the appearance of the first soft drusen, a distinct course at a gradual pace that accelerates with increasing age.

ABCC6/MRP6 mutations: further insight into the molecular pathology of pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a hereditary disease characterized by progressive dystrophic mineralization of the elastic fibres. PXE patients frequently present with skin lesions and visual acuity loss. Recently, we and others showed that PXE is caused by mutations in the ABCC6/MRP6 gene. However, the molecular pathology of PXE is complicated by yet unknown factors causing the variable clinical expression of the disease. In addition, the presence of ABCC6/MRP6 pseudogenes and multiple ABCC6/MRP6-associated deletions complicate interpretation of molecular genetic studies. In this study, we present the mutation spectrum of ABCC6/MRP6 in 59 PXE patients from the Netherlands. We detected 17 different mutations in 65 alleles. The majority of mutations occurred in the NBF1 (nucleotide binding fold) domain, in the eighth cytoplasmatic loop between the 15th and 16th transmembrane regions, and in NBF2 of the predicted ABCC6/MRP6 protein. The R1141X mutation was by far the most common mutation identified in 19 (32.2%) patients. The second most frequent mutation, an intragenic deletion from exon 23 to exon 29 in ABCC6/MRP6, was detected in 11 (18.6%) of the patients. Our data include 11 novel ABCC6/MRP6 mutations, as well as additional segregation data relevant to the molecular pathology of PXE in a limited number of patients and families. The consequences of our data for the molecular pathology of PXE are discussed.

A pooled case-control study of the apolipoprotein E (APOE) gene in age-related maculopathy

Age-related maculopathy (ARM) is a multifactorial disorder known to have a substantial genetic component. The epsilon4 allele of the apolipoprotein E gene (APOE-4) has previously been reported to have a protective effect on ARM risk, while the APOE-2 allele may increase disease risk. This study combined four independent data sets (three US and one European) of Caucasian ARM patients and controls in order to obtain better statistical power to examine the role of APOE in ARM. APOE genotype and allele frequencies were compared for 617 ARM cases and 1260 controls, adjusting for age and sex differences between the two groups via multiple logistic regression. The protective effect of the APOE-4 allele on ARM risk was confirmed (age- and sex-adjusted odds ratio (OR) for APOE-4 carriers 0.54, 95% confidence interval (CI) 0.41-0.70, p < 0.0001). The effect of APOE-4 did not differ significantly between males and females and was observed consistently for both atrophic and neovascular ARM. Evidence for an increased risk of ARM due to the APOE-2 allele was found for men, but not for women (OR for men 1.54, 95% CI 0.97-2.45; OR for women 0.74, 95% CI 0.52-1.06, p = 0.01 for interaction of sex and APOE-2 carrier status). These data confirm that the APOE-4 allele, or an allele in linkage disequilibrium with it, reduces the risk of ARM. They also suggest that the effect of the APOE-2 allele may vary by gender, and that APOE-2 may confer an increased risk only to males.

Macular pigment and melanin in age-related maculopathy in a general population

PURPOSE

It has been suggested that macular pigment (MP) and melanin may protect against age-related maculopathy (ARM). To check this, MP and melanin optical density were measured in a random population-based sample of subjects 55 years of age or older.

METHODS

Spectral fundus reflectance of the fovea was measured in one eye per subject in a 2.3 degrees detection field with a fundus reflectometer. The sample consisted of 199 men and 236 women. Analysis with a fundus reflectance model yielded individual estimates for the MP and melanin optical density. Diagnosis of ARM was based on grading of standardized fundus transparencies. Eyes were stratified in four exclusive stages of ARM.

RESULTS

MP optical density (at 460 nm) was 0.33 +/- 0.15 in eyes without ARM (n = 289) and 0.33 +/- 0.16 in eyes at any stage of ARM (n = 146). Melanin optical density (at 500 nm) was 1.18 +/- 0.19 in eyes without ARM and 1.20 +/- 0.21 in eyes at any stage of ARM. We found no gender differences for either MP or melanin optical density.

CONCLUSIONS

No differences in MP and melanin optical density were found between eyes with and without ARM or between the various ARM stages.

Comparing ophthalmoscopy, slide viewing, and semiautomated systems in optic disc morphometry

PURPOSE

To compare disc measurements obtained by indirect ophthalmoscopy, the Heidelberg Retina Tomograph (HRT), stereoscopic slide viewing (SSV) of color transparencies, and the Topcon ImageNet System (ImageNet).

DESIGN

Population-based cross-sectional study.

METHODS

From the Rotterdam Study, 324 subjects (567 eyes) were nonselectively included. All underwent a full ophthalmologic examination in mydriasis. Vertical cup/disc ratios (VCDRs) were compared between all four methods and disc area (mm(2)), neural rim area (mm(2)), cup area (mm(2)), and cup volume (mm(3)) between HRT and ImageNet.

RESULTS

Mean VCDR for ophthalmoscopy was 0.25 (standard error [SE], 0.007), for HRT 0.42 (SE, 0.008), for SSV 0.39 (SE, 0.010), and for ImageNet 0.50 (SE, 0.006). The correlation for VCDR between ophthalmoscopy, the two devices, and SSV was 0.42, respectively 0.57; between ImageNet and HRT 0.75. The 97.5th percentiles of the VCDR for ophthalmoscopy, HRT, SSV, and ImageNet were 0.80, 0.73, 0.80, and 0.73, respectively; the 99.5th percentiles thus were 0.90, 0.79, 0.86, and 0.79. The mean disc area, rim area, cup area, and cup volume were 2.08, 1.63, 0.45 mm(2) and 0.09 mm(3) for HRT, and 2.39, 1.77, 0.61 mm(2) and 0.16 mm(3) for ImageNet, respectively. The corresponding correlations for these four parameters were 0.67, 0.42, 0.81, and 0.82.

CONCLUSIONS

Different techniques lead to considerable differences in disc morphometric values. ImageNet produced higher mean values compared with HRT and ophthalmoscopy. Ophthalmoscopy showed the lowest correlations and SSV the highest ones with the two semiautomated devices. Between ImageNet and HRT the correlation for all parameters was high except for the neural rim area.