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Cryostat sections of skin biopsies from 83 patients with benign or malignant cutaneous lymphoid infiltrates were examined immunohistologically for reactivity with Ki-67 (a monoclonal antibody recognizing a nuclear antigen expressed by cycling cells) using the APAAP immunoalkaline phosphatase labeling method and a double immunoperoxidase/alkaline phosphatase staining technique. Ki-67-positive neoplastic lymphocytes were plentiful in all large-cell lymphoma cases and in one-third of the small-cell lymphomas. Some benign disorders (patch test biopsies, cutaneous lymphocytoma, lichen planus) also contained many Ki-67-positive lymphocytes. These data indicate the value of using Ki-67 to assess the proliferative capacities of the lymphoid cells in cutaneous infiltrates. Use of this technique in the future may have important prognostic and therapeutic implications in the management of cutaneous lymphoid malignancies.

The antigenic properties of normal epidermal Langerhans cells and their neoplastic counterparts (histiocytosis X cells) were compared with those of other types of macrophages, by immunohistochemical staining of skin and lymph node biopsies with a panel of mono-clonal antibodies. The phenotype of Langerhans cells, histiocytosis X cells, dermal macrophages and interdigitating reticulum cells were similar (HLA-DR+, OKT 6+/-, Leu3+/-, C3-receptor-, Ig-complex-, R4/23-, MO2-), and differed markedly from those of follicular dendritic cells (HLA-DR-, OKT6-, Leu3-, C3 receptor+, Ig+, R4/23+, MO2-, and histiocytic reticulum cells (HLA-DR+/-, OKT6-, Leu3+/-, C3-receptor+, Ig-complex+, R4/23-, MO2+/-). This indicates that Langerhans cells are related to the interdigitating reticulum cells found in the T cell areas of lymphoid organs, and demonstrates that Langerhans cells do not express C3b, C3bi or C3d receptor molecules. Our data also emphasise that the Leu3 antigen is not restricted to cells of the T cell lineage.

Cryostat sections from fully developed papular lesions of lymphomatoid papulosis (histologic subtype A or B) have been examined by immunoenzymatic staining with 24 monoclonal antibodies against lymphoid cells and their subsets. The lesions demonstrated essentially identical cellular compositions and consisted of T-lymphocytes with a peripheral phenotype (Lyt3+, anti-Leu-4+, OKT6-), macrophages (HLA-DR+, EB11+, OKM1+), and Langerhans cells (HLA-DR+, OKT6+). T-helper/inducer cells (anti-Leu-3+) usually dominated over T-suppressor/cytotoxic cells (anti-Leu-2+). In all cases, proportions of the infiltrating T-cells expressed markers associated with activation (HLA-DR, the OKT1O antigen, interleukin-2 receptor) or proliferation (transferrin receptor, the Ki-67 antigen) of lymphoid cells. Furthermore, the infiltrates contained clusters and/or sheets of large cells reactive with antibodies (Ki-1, Ki-24, Ki-27), which recognize Hodgkin's and Reed-Sternberg cells. These data indicate an origin of the cellular infiltrate from transformed or activated lymphoid cells and suggest an interrelationship of lymphomatoid papulosis to Hodgkin's disease.

The practical usefulness of a panel of monoclonal antibodies recognising epithelial and lymphoid antigens has been evaluated on a series of 10 routinely processed thyroid tumours of uncertain origin. All 6 small cell tumours were shown to be of lymphoid origin whereas of the 4 large cell tumours two were lymphomas and two carcinomas. Two of the tumours, one large cell and one small cell, were undiagnosable due to technical reasons (crush artefact or small size of biopsy) and emphasized the value of immunohistology in this context. Clinical follow-up of all 10 cases indicated that these distinctions are of both prognostic and therapeutic value. It is concluded that immunocytochemistry using a carefully selected panel of monoclonal antibodies is a valuable and convenient means of making an objective distinction between anaplastic thyroid tumours of epithelial or lymphoid origin.