DETECTION OF IGA SUBCLASSES AND J-CHAIN MESSENGER-RNA BEARING PLASMA-CELLS IN HUMAN DENTAL PERIAPICAL LESIONS BY IN-SITU HYBRIDIZATION

Humoral immune responses are implicated in the pathogenesis of human d ental periapical lesions. To elucidate whether Iga-associated immune s ystems play a role in the lesions, the in situ hybridization technique was used to detect J chain mRNA expression, which is correlated with the secretion of dimeric IgA. In addition, IgA subclass mRNA-expressin g cells were also investigated by double target in situ hybridization (ISH) methodology using digoxigenin- and biotin-labeled IgA subclass s pecific oligonucleotide probes. This double target ISH technique invol ved immunochemical detection with an alkaline phosphatase-conjugated a ntibody and a peroxidase conjugated avidin-biotin complex system to de tect IgA subclass mRNA in the formalin-fixed, paraffin wax embedded pe riapical tissue sections. Twenty-four biopsy samples (16 periapical gr anulomas and 8 radicular cysts) were examined. IgA subclass mRNA posit ive plasma cells were detected in all samples. IgA1 mRNA-expressing ce lls were predominant both in granulomas and cysts (mean = 75.3 a 11.2% , 64.8 a 21.3%, respectively), and the IgA1 propertion was higher in g ranulomas than in cysts, although no significant difference was seen b etween the two lesions (p = 0.132). J chain mRNA positive cells were v ery sparsely detected in 21/24 cases. The median percentages of J chai n mRNA positive cells/IgA mRNA positive plasma cells (4.7%, range 0.3 -13.6%) in cysts were significantly higher than in granulomas (1.3%, r ange 0-7.7%; p = 0.03). This result supports the hypothesis that dimer ic IgA may be more actively produced in radicular cysts than in granul omas. These features are thought to reflect the local activation of th e periapical immune system in response to environmental factors and in dicate that secretory IgA mediated immune defense systems appear to pl ay little role in these lesions. Our results indicate that the IgA-ass ociated immune response in periapical lesions is more similar to serum or systemic IgA responses than to mucosa-associated immune responses where dimeric IgA predominates.