Immune privilege disruption in folliculotropic mycosis fungoides: investigation of major histocompatibility complex antigen expression

Background: Folliculotropic mycosis fungoides (FMF) is a cutaneous T-cell lymphoma mainly affecting the hair follicle, which seems to represent a place of immune privilege phenomenon. Objectives: To explore a possible role of immune privilege (IP) in FMF analyzing the major histocompatibility complex (MHC) expression. Methods: Immunohistochemistry for HLA-G and MHC-II was performed to formalin-fixed paraffin-embedded cutaneous skin biopsies of FMF patients (n = 43), conventional mycosis fungoides (CMF; n = 13), alopecia areata (AA; n = 13), and normal scalp skin (NS; n = 12). Results: HLA-G expression was lower in FMF (34%: 14/41) and CMF (18%: 2/11) groups compared to alopecia areata (92%:11/12) and normal scalp skin group (100%: 12/12). MHC-II expression in hair follicle was greater in the FMF group (18/42: 43%) compared to AA (0%) and NS (0%). HLA-G and MHC-II expression in cellular infiltrate had no difference among FMF and CMF groups and was different compared to the AA group. Conclusions: Our data support the hypothesis of disruption of immune privilege based on the lower expression of HLA-G and higher expression of MHC-II in the follicular epithelium in mycosis fungoides compared to alopecia areata and normal scalp skin. The lack of difference between FMF and CMF groups did not support the role of these molecules as a driver of folliculotropism. The expression of MHC molecules seems to be different between neoplastic and inflammatory infiltrates. The definitive significance of expression of the MHC molecules remains unclear, and more studies are necessary to fully understand the role of these molecules in cutaneous lymphomas.