Detection of IL-15 in early CTCL lesion (patch stage) by an IL-15 antibody. The binding of the specific antibody to IL-15 was detected by an alkaline phosphatase (AP) coupled second antibody directed against the Fc region of the IL-15 antibody. Binding of the IL-15 antibody after APAAP staining was strongest in the junction zone between epidermis and dermis where CTCL cells show their highest densities. The specificity of the binding of the IL-15 antibody was tested by a competition experiment with recombinant IL-15 (not shown).