Analysis of immunoglobulin-synthesizing cells in human dental periapical lesions by in situ hybridization and immunohistochemistry.

Immunoglobulin (Ig) kappa (kappa) and lambda (lambda) light chain mRNA-expressing cells were investigated by in situ hybridization (ISH) to assess the local humoral immune response in human dental periapical lesions. Twenty-seven biopsy samples (17 periapical granulomas and 10 radicular cysts) were examined. Both types of light chain mRNA-positive cells were detected in formalin-fixed/paraffin-embedded tissue sections in all samples. Plasma cells showed weak to strong cytoplasmic staining with both probes and background staining was negligible. The ISH methodology is specific and sensitive in detecting Ig light chain mRNAs and retains cell morphology well. kappa to lambda ratios showed moderate variability for both granulomas and cysts (mean = 1.66 +/- 0.85 SD, 1.47 +/- 0.51, respectively). There was no significant difference in light chain distribution between granulomas and cysts. Ig kappa and lambda light chain proteins were also studied by immunohistochemistry (IHC) but the results were disappointing due to excessive background staining. This study confirms that Ig is locally produced in periapical lesions and that the ISH method localises Ig light chain-containing cells better than IHC. The wide variability in kappa/lambda ratio may support the concept of non-specific multibacterial infection in these lesions.