Ultrastructural identification of T lymphocytes in tissue sections of mycosis fungoides

An immunoelectronomicroscopic method has been employed to demonstrate in situ the T lymphocyte nature of the dermal and epidermal infiltrates to mycosis fungoides. A specific antiserum to the human T lymphocyte surface antigen (HTLA) was used in an indirect reaction with a peroxidase labeled anti-immunoglobulin. After histochemically revealing the peroxidase activity, T cells were easily identified by the deposition of electron dense material on the cytoplasmic membrane. Counterstaining with uranyl acetate and lead citrate enabled us morphologically to observe the maturity of infiltrating T lymphocytes and to identify Sézary cells and other cells such as eosinophils in the infiltrate. Our results confirm the T cell nature of the dermal infiltrate in mycosis fungoides and show that the epidermal infiltrate of cells forming Pautrier micro-abscesses are predominantly T lymphocytes.