Immunocytology of plasmacytoid T cells: marker analysis indicates a unique phenotype of this enigmatic cell.

Clusters of plasmacytoid T cells (PTC) were detected in axillary lymph nodes draining an invasive ductal breast cancer in a 64-year-old woman. Immunocytology of PTC revealed a remarkable antigenic profile. Analysis with a broad spectrum of monoclonal antibodies demonstrated that PTC bear the CD4 surface antigen (Leu-3a+ and OKT4+), the transferrin receptor (OKT9+), and components of the HLA class-II antigens (TU35+, TU39+, Leu-10+). Surprisingly, PTC were stained by two monoclonal antibodies recognizing monocytes and macrophages (Ki-M6 and Ki-M7). Finally, Leu-8, which detects most mature T lymphocytes, also identified the PTC, and all pan T-cell markers (Leu-1, UCHT 1, and Lyt 3) were constantly negative. The cytogenesis and the functional properties of PTC remain a matter of discussion.