Expression of follicular helper T-cell markers in primary cutaneous T-cell lymphoma

The follicular helper T cells (TFH) seemed to be expressed in several subsets of T-cell lymphomas. However, their expression in cutaneous T-cell lymphomas (CTCLs) has been rarely described. We investigated the clinical features, histopathological morphology, and expression of TFH markers in CTCLs. Forty-nine patients (24 men and 25 women) diagnosed with CTCL were examined, 25 patients with mycosis fungoides (MF) and 24 with other CTCLs. Immunohistochemical staining for CD10, Bcl-6, inducible costimulator, CXCL13, and PD-1 were performed. Relation between PD-1 and clinical course in MF was evaluated. PD-1 was detected in 21 of 25 (84.0%) MF cases and in 11 of 24 (45.8%) other CTCL cases. Bcl-6, CXCL13, inducible costimulator, and CD10 were occasionally expressed in most T-cell lymphomas, including MF. The staining for PD-1 was negative in all the MF cases with large-cell transformation. No correlation was observed between disease course and PD-1 expression rate in the MF cases. In conclusion, among the TFH markers, PD-1 was most frequently expressed in CTCL. PD-1 was expressed in most MF. PD-1 expression rates were significantly higher in MF than in other CTCLs.