INVESTIGATION OF EPIDERMOTROPISM IN CANINE MYCOSIS-FUNGOIDES - EXPRESSION OF INTERCELLULAR-ADHESION MOLECULE-1 (ICAM-1) AND BETA-2 INTEGRINS

In human mycosis fungoides (MF), interactions between LFA-1 (CD11a/CD1 8) and ICAM-1 (CD54) are involved in lymphocyte adhesion to keratinocy tes. The purpose of this study was to evaluate the expression of ICAM- 1, beta-2 integrins and class II major histocompatibility complex mole cules (MHC II) on keratinocytes and infiltrating lymphocytes in canine MF. Sections of frozen skin biopsy specimens from normal dogs (n = 3) and dogs with MF (n = 17) were evaluated by immunohistochemistry for expression of ICAM-1, beta-2 integrins, and class II MHC molecules. Ou r results demonstrated that in canine MF, ICAM-1 was expressed variabl y on epidermal and follicular keratinocytes. The extent of keratinocyt e ICAM-1 expression did not correlate with the degree of lymphocyte ep ithelial infiltration, nor with lymphocyte LFA-1 expression. This was especially evident in cases of Pagetoid reticulosis-like disease in wh ich prominent lymphocyte epidermotropism was not accompanied by kerati nocyte ICAM-1 expression. Keratinocyte class II MHC molecule expressio n did not correlate with keratinocyte ICAM-1 expression. In conclusion , in canine MF, the lack of statistically significant correlations bet ween epithelial lymphocyte infiltration and keratinocyte ICAM-1 expres sion, and between keratinocyte ICAM-1 and lymphocyte LFA-1 staining, s uggests that the LFA-1/ICAM-1 pathway is not the major adhesion mechan ism between lymphocytes and keratinocytes. It is suspected that differ ent ligands of the LFA-1 integrin (e.g. ICAM-2) or other adhesion mole cules (e.g. CD2/LFA-3, VLA-1) might be involved in the epitheliotropis m phenomenon in canine MF. These hypotheses cannot be evaluated in the dog at this time owing to the lack of specific monoclonal antibodies.