Immunohistochemical detection of skin-homing T cells expressing fucosyltransferase VII (Fuc-TVII) in vitro and in situ.

Although expression of cutaneous lymphocyte-associated antigen (CLA) is thought to be a specific marker of skin "homing" T cells, it has become clear that CLA is a good marker for high levels of fucosyltransferase VII (Fuc-TVII) activity but does not necessarily represent the epitope required for binding to E-selectin (Wagers et al, 1996, 1997). Therefore, expression of Fuc-TVII is an attractive candidate for identifying skin "homing" T cells. However, analyses of Fuc-TVII expression in human T cells have been performed only at the mRNA level (Nakayama et al, 2000) because of the lack of mAB: In this study Fuc-TVII was for the first time visualized in individual cells by using a novel mAb that we developed. Double immunofluorescence and immunohistochemistry demonstrated the coexpression of Fuc-TVII and CLA in cell lines in which Fuc-TVII mRNA was shown to be expressed at high levels: whereas CLA expression was seen in the cell membrane, Fuc-TVII was identified in a supra- or perinuclear location. Cytoplasmic Fuc-TVII expression was also detectable in both CD4(+) and CD8(+) T cells purified from peripheral blood. Fuc-TVII was also expressed at high levels in many CLA(+) T cells infiltrating the skin. In these peripheral T cells, unlike in cell lines, cytoplasmic expression of Fuc-TVII was not always associated with surface CLA expression. This mAb would serve as a valuable tool for selectively identifying a novel subset of skin "homing" T cells that are not detected by the conventional method because of the lack of CLA expression.