Lectin histochemistry of malignant tumors. II. Concanavalin A: a new histochemical marker for macrophage-histiocytes in follicular lymphoma.

Concanavalin agglutinin (Con A) binding sites were studied in paraffin embedded lymph node specimens of reactive follicular hyperplasia (12 cases) and follicular lymphoma (37) using the avidin-biotin-peroxidase complex method, and the results were compared with those of Peanut agglutinin (PNA) and lysozyme stains. Very similar to the PNA stain, two categories of Con A receptor sites were observed: cytoplasmic and cell surface. In the reactive lymph nodes, the cells showing cytoplasmic receptor sites (CR+ cells) corresponded to macrophage-histiocytes and possibly dendritic reticulum cells in the H & E stained sections, while those showing cell surface receptor sites (SR+) corresponded to lymphoid cells. Unlike the PNA binding, however, the staining reaction of SR+ lymphoid cells was weak, and another staining pattern, a dot-like stain, was observed in some lymphocytes, both SR+ and SR-. In follicular lymphomas, CR+ histiocytes were distinctly displayed within the follicular centers in 25 of 37 cases, including 12 cases in which PNA stains on adjacent or nearby sections were negative for intrafollicular macrophage-histiocytes. Similarly, Con A stains were positive for the intrafollicular CR+ cells in four of the five cases in which lysozyme stains were negative. Many of these intrafollicular CR+ cells contained inclusion-like cytoplasmic globules and/or vacuoles, a hallmark of the large CR+ cells of germinal centers. These observations suggest that macrophage-histiocytes of presumably germinal center origin are retained in neoplastic follicular centers in varying degrees, and Con A might be a useful marker for macrophage-histiocytes in paraffin-embedded routine pathological specimens, in addition to the currently accepted markers, PNA and lysozyme.