Expression of CD158k and VIM by circulating and cutaneous lymphocytes. (A) Flow cytometry analysis in patient 11 showed CD158k^dim and cell-surface VIM positivity before treatment (top row). After treatment with extracorporeal photochemotherapy, there was a dramatic decrease in the CD4⁺ population associated with a loss of CD158k expression and a significant increase in VIM (bottom row). (B) RT-PCR for CD158k was positive for PBMCs in patients 1, 2, 3, and 4 and for the Sézary cell line Pno, whereas it was negative for CD4⁺ lymphocytes in a healthy donor. (C) Immunohistochemistry analysis performed in a skin sample from patient 3 showed a predominantly CD3⁺CD4⁺ infiltrate along with CD158k⁺ cells in the dermis and the epidermis. Intraepidermal nests of lymphocytes, or Pautrier microabscesses, can be seen (arrows). Few CD8⁺ lymphocytes were present in the dermis (arrowheads), whereas only CD4⁺ T cells are seen in the epidermis. Slides are shown at 200 × original magnification (20 ×/0.50 NA objective), and images were captured with an Axioskop2 microscope (Zeiss, Oberkochen, Germany). Pictures were scanned in with a DP70 camera and software (Olympus, Hamburg, Germany). Hematoxylin and eosin staining is shown on the left, whereas a biotin/avidin system conjugated to alkaline phosphatase was used for CD3, CD4, CD8, and CD158k labeling.