Dermal dendrocytes and T‐cells in canine mycosis fungoides. Support for an animal model of human cutaneous T‐cell lymphoma

Background. An extensive upper dermal network of human Thy‐1+/Factor XIIIa+ dermal dendrocytes (DD) exists in human mycosis fungoides (MF). Methods. Immunophenotyping and morphologic studies on serial frozen and paraffin sections from 15 cases of canine MF were performed to see if a similar network exists in this disease, as has been proposed as an animal model of human MF. Primary antibodies were anti‐human Factor XIIIa, Factor XIIIs, anti‐canine Thy‐1, CD4, CD8, CD18, CD45RA, Class II, MAC387, KP‐1, EBM‐11, and several other pan‐T, pan‐B, and pan monocyte markers. Results. Thy‐1+/Factor XIIIa+DD were seen in all cases and confirmed on identical cells by double immuno‐fluorescence. These were seen throughout the upper dermis, similar to DD in human MF. Canine DD expressed the macrophage marker 2A2+, and were Class II+, CD4+, CD8‐, CD18+, EBM11‐, Factor XIII‐, MAC387‐, and KP‐1. Epidermal and dermal lymphocytes in canine MF were Thy‐1‐, CD4+, CD8‐, CD18+, CD45RA‐, EBM11‐, MAC387‐, Factor XIIIa‐, Factor XIIIs‐ in some cases, whereas others had a predominance of CD8+ lymphocytes. Conclusions. Thus, canine MF is immuno‐phenotypically similar to human MF. Additional support for this disease as a model of human MF is demonstrated by the rich network of Thy‐1+/Factor XIIIa+ DD in the upper dermis of canine MF similar to human MF.