Immunohistochemical classification of primary and recurrent macular corneal dystrophy in Germany: subclassification of immunophenotype I A using a novel keratan sulfate antibody.

Macular corneal dystrophy (MCD) is an autosomal recessive disease characterized by abnormal deposition of glycosaminoglycans in corneal stroma, keratocytes, Descemet's membrane and corneal endothelium. According to the presence and distribution of sulfated keratan sulfate (KS)-epitopes in serum and cornea (using mAb 5-D-4), MCD can be classified into three immunophenotypes: type I, I A and II. The purpose of this study is to evaluate the immunophenotype of primary and recurrent MCD and to analyze the reactions of a novel KS-antibody in MCD corneas, which recognizes an epitope localized in the binding region of KS-chains to the core protein (mAb 3D12/H7). Indirect immunohistochemistry for KS (mAbs 3D12/H7 and 5-D-4) was performed on 44 corneas of 37 patients with MCD including two recurrences. Immunogold labeling was used to localize KS ultrastructurally within keratocytes. The serum concentration of KS (cKS) was determined in a serum antigen-inhibition assay. Immunohistochemically, no reaction was observed using mAb 5-D-4 in 18 corneas of 16 patients (43% of 37 patients; immunophenotype I). Positive reactions within single keratocytes but not in the stroma, were seen in 22 corneas of 17 patients (46% of 37 patients; immunophenotype I A) and positive reactions in keratocytes and extracellular stroma were found in four corneas of four patients (11% of 37 patients: immunophenotype II). For analysis of cKS a total of seven samples was available. Whereas in the samples of the five patients with immunophenotypes I and I A cKS was below the limit of detection, in the two sera from patients with immunophenotype II, cKS was normal (cKS = 1243 and 1380 nmol l(-1)). The two recurrences demonstrated immunophenotype II. Using mAb 3D12/H7, MCD immunophenotype I A can be further subclassified in type I A 1 (lacking reaction with mAb 3D12/H7 in keratocytes; 77%) and type I A 2 (positive reaction with mAb 3D12/H7 within keratocytes; 23%). MCD immunophenotype I A can not only be found in Saudi Arabia, but is as common as immunophenotype I in German patients. The only recurrences of MCD necessitating regrafting occurred in two patients with immunophenotype II possibly suggesting a higher risk for recurrence in this immunophenotype. The mAb 3D12/H7 allows a further subclassification of immunophenotype I A into type I A1 and 2. This points to a broader spectrum of MCD immunophenotypes and indirectly to a broader corneal proteoglycan pathology in MCD.