Application of Leu M5 (CD 11c) antibody in the cytodiagnosis of body fluids: preliminary results.

Identification of metastatic malignant cells in body fluids and their distinction from reactive mesothelial cells is a common diagnostic problem. Application of the immunoalkaline phosphatase method using epithelial membrane antigen, cytokeratin, vimentin, carcinoembryonic antigen, lysozyme, and leukocyte common antigen (CD 45) is routinely performed in our Hematology Laboratory in conjunction with morphological examination of body fluids. Recently, we found that anti-Leu M5 (CD 11c), a monoclonal antibody to human monocyte/macrophage, is frequently reactive to mesothelial cells. We then undertook a prospective study, adding anti-CD 11c to the above-listed antibody panel and applying to cytocentrifuge preparations of body fluid. The neoplastic cells in only 2 out of 34 cases (5.9%) with the diagnosis of metastatic carcinomas reacted positively for CD 11c. The neoplastic cells in four cases of malignant lymphoma were non-reactive for CD 11c. In addition, malignant cells on touch preparations of 25 carcinomas were also negative. Mesothelial cells in all 15 cases of reactive effusions and those mesothelial cells present in malignant effusions were positively stained with CD 11c, although the intensity of staining varied in different mesothelial cells of the same cases. We conclude that anti-CD 11c can be considered as a useful adjunct to the differential diagnosis of malignant effusions.