Relative distribution of plasma cells expressing immunoglobulin G subclass mRNA in human dental periapical lesions using in situ hybridization.

Immunoglobulin G (IgG)-producing plasma cells are the predominant immunoglobulin secreting plasma cells in human dental periapical lesions, compared with immunoglobulin A- and immunoglobulin M-producing plasma cells. In this study, the cells expressing mRNA, that encoded the distinct IgG subclasses, were detected using an in situ hybridization technique in 25 periapical lesions. These lesions consisted of 14 periapical granulomas and 11 radicular cysts. Four oligonucleotide probes were chemically synthesized from IgG subclass-specific hinge region genes to ensure specificity of the probes. Plasma cells expressing mRNA, which coded for the IgG subclasses, were detected in formalin-fixed/paraffin wax-embedded sections. Background staining was negligible in all of the sections tested. The in situ hybridization method used in this study was both specific and sensitive for the detection of mRNA encoding each of the four distinct IgG subclasses, whereas the cells retained good morphology. The relative proportions of plasma cells expressing each of the IgG subclass-specific mRNAs in both granulomas and cysts were as follows: IgG1 (57.4 and 55.5%); IgG2 (34.1 and 34.6%); IgG3 (4.0 and 4.3%); and IgG4 (4.0 and 5.5%). There were no significant differences between the percentages of plasma cells expressing each of the IgG subclass mRNAs between the two types of lesions. IgG1 producing plasma cells comprised the highest proportion of IgG-producing plasma cells in both types of periapical lesion. IgG2-producing plasma cells were next in abundance, followed by plasma cells for either IgG3 or IgG4, which were in roughly equivalent numbers.

Detection of IgA subclasses and J chain mRNA bearing plasma cells in human dental periapical lesions by in situ hybridization.

Humoral immune responses are implicated in the pathogenesis of human dental periapical lesions. To elucidate whether IgA-associated immune systems 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-expressing cells were also investigated by double target in situ hybridization (ISH) methodology using digoxigenin- and biotin-labeled IgA subclass specific oligonucleotide probes. This double target ISH technique involved immunochemical detection with an alkaline phosphatase-conjugated antibody and a peroxidase conjugated avidin-biotin complex system to detect IgA subclass mRNA in the formalin-fixed, paraffin wax embedded periapical tissue sections. Twenty-four biopsy samples (16 periapical granulomas and 8 radicular cysts) were examined. IgA subclass mRNA positive plasma cells were detected in all samples. IgA1 mRNA-expressing cells were predominant both in granulomas and cysts (mean = 75.3 +/- 11.2%, 64.8 +/- 21.3%, respectively), and the IgA1 proportion was higher in granulomas than in cysts, although no significant difference was seen between the two lesions (p = 0.132). J chain mRNA positive cells were very sparsely detected in 21/24 cases. The median percentages of J chain 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%, range 0-7.7%; p = 0.03). This result supports the hypothesis that dimeric IgA may be more actively produced in radicular cysts than in granulomas. These features are thought to reflect the local activation of the periapical immune system in response to environmental factors and indicate that secretory IgA mediated immune defense systems appear to play little role in these lesions. Our results indicate that the IgA-associated immune response in periapical lesions is more similar to serum or systemic IgA responses than to mucosa-associated immune responses where dimeric IgA predominates.