Analysis of monoclonal T cells in benign dermatoses related to mycosis fungoides.

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Pityriasis lichenoides has been regarded as a benign inflammatory disorder belonging to the parapsoriasis group. However, based on its association with cutaneous T cell lymphoma (CTCL) or the presence of monoclonal populations in infiltrates, it has been hypothesized that pityriasis lichenoides is part of the CTCL disease sectrum. For validation of this hypothesis, the monoclonal populations in pityriasis lichenoides should express the same phenotype as CTCL CID4^+ Tlymphocyte.In this study, we analysed infiltrates in 7 cases of pityriasis lichenoides (6 cases of pityriasis lichenoides et varioliformis acuta and one case of pityriasis lichenoides chronica) using praffin-embedded specimens.1. By amplifying the rearranged TCR-γ genes, monoclonal populations were detected in 6 of 7 cases of pityriasis lichenoides.2. These amplified bands were recovered and sequenced. These data showed that the PCR-based method adequately amplified the rearranged TCR-γ genes and specified the gene segments used in the rearrangement processes.3. We prepared pairs of mirror sections that gave the same histological picture as a mirror image. In each pair, in-situ hybridization (ISH) using the amplified band as a probe on one section and immunohistochemistry using UCHL1, anti-CD8, or anti-CD4 antibodies on the other section were performed. By comparing these sections, the phenotypes of the ISH-positive cells were determined as UCHL1^+, CD8^-, CD4^+ cells.These results demonstrated that pityriasis lichenoides qualified as a member of parapsoriasis. Furthermore, we suggest that the interrelationship between monoclonal CD4^+ cells and reactive CD8^+ cells affects the biological behavior of the disease in the CTCL disease spectrum.