Detection of monocyte/macrophage cell populations in effusions: a comparative study using flow cytometric immunophenotyping and immunocytochemistry.

The objective of the present study was to compare the efficiency of immunophenotyping using flow cytometry (FCM) and immunocytochemistry (ICC) in the detection of macrophages in serous effusions. Cytoblock sections from 90 effusions were stained for the monocyte/macrophage marker CD14, using ICC. Fresh-frozen samples of all cases were analyzed for CD14 expression, using FCM. Epithelial, lymphoid, and mesothelial cell populations were identified using antibodies against Ber-EP4, CD45, and N-cadherin, respectively. Results were compared with clinical parameters and morphological diagnosis. Thirty-nine specimens were cytologically diagnosed as malignant, containing tumor cells of nonhematologic origin, whereas 46 were interpreted as benign. Two additional specimens were diagnosed as indeterminate or suspicious for malignancy, and 3 specimens contained lymphoma cells. CD14-positive cells were detected in 85/90 (94%) of effusions using FCM, and in all 90 specimens using ICC. The percentage of CD14-positive cells was highly variable, but in some specimens was as high as 76% using FCM and 85% using ICC. A good association was observed between the two methods in the detection of CD14-positive cells (P < 0.001). The presence of macrophages in effusions showed an association with female gender, using both FCM (P = 0.002) and ICC (P = 0.011), but none with effusion site, patient age, clinical and cytological diagnosis, or presence of Ber-EP4-positive cells (P > 0.05). The presence of Ber-EP4-positive cells showed a strong association with the cytological diagnosis of malignancy (P < 0.001). In conclusion, macrophages are a significant cell population in effusions, of both benign and malignant etiology, due to both their size and their possible confusion with cancer cells. Both FCM and ICC aid in the recognition of these cells, and thus provide an effective tool for the identification of different cell populations in effusions.