The behavior of Langerhans cells in skin tumors was investigated by immunohistochemical techniques using OKT6. OKT6-positive cells were numerous in squamous cell carcinomas, seborrheic keratoses and keratoacanthomas. They were rare in basal cell carcinomas, Bowen’s disease, eccrine poromas, extramammary Paget’s disease and warts. In solar keratosis, the number of OKT6-positive cells was almost equal or slightly larger compared to the normal epidermis. These results indicate that the density of Langerhans cells may not correlate with the degree of malignancy but, to a certain extent, with the nature of the membrane of tumor cells occurring e.g. during keratinization.

An immunoperoxidase study of 2 cases of adult T cell leukemia (ATL) and 2 cases of mycosis fungoides (MF) was done using monoclonal antibodies. In ATL, many anti‐interleukin‐2 receptor antibody (LeuIL‐2R)‐positive cells were seen in the dermis and occasionally in the epidermis. In contrast, in MF, LeuIL‐2R‐positive cells were much less frequent. LeuIL‐2R‐positive cells in MF may be non‐malignant T cells; not all LeuIL‐2R‐positive cells may be malignant in ATL. These non‐malignant LeuIL‐2R‐positive cells, we suggest, are involved in the interaction between malignant T cells and reactive infiltrating cells. Furthermore, in addition to OKT6‐positive cells, OKM1‐positive cells were seen in the infiltrates in the dermis in both ATL and MF. OKM1‐positive cells also participate in the mechanism of the skin affinity in ATL and cutaneous T cell lymphomas.