In situ immunologic characterization of follicular lymphomas.

Surface markers were studied in a series of follicular lymphomas with immunofluorescence on frozen sections (39 cases) and on cell suspensions (21 cases), and with immunoperoxidase on frozen sections using a panel of 15 monoclonal antibodies (17 cases). With immunofluorescence on frozen sections, 22/39 cases showed monotypic sIg (IgMK: 14 cases, IgML: 7 cases, M: 1 case). In the remaining 17 cases the neoplastic follicles were negative. Nevertheless, even if sIg is not detected, the absence of an extracellular immunoglobulin network is indicative of the neoplastic, and not of the reactive nature of lymphoid follicles. The results obtained with immunofluorescence on frozen sections and on cell suspensions were identical in about half of the cases. In 9/21 cases monotypic sIg were detected by only one of these two methods. All the 17 cases studied with immunoperoxidase on frozen sections using monoclonal antibodies demonstrated monotypic sIg. On low magnification 6/17 sIg+ exhibited a nodular staining pattern while 7/17 cases this staining was diffuse. In 4/17 cases the staining pattern for heavy and light chains was different. A thin mantle zone, with sIgM plus sIgD cells, was observed in only 4 cases. Anti-HLA-DR and Leu-10 were positive in all cases. T cells positive for OKT3 were mainly distributed in the interfollicular areas; OKT4+ cells outnumbered OKT8+ cells. Within the neoplastic follicles, T cells stained mainly for OKT4 and OKT8+ cells were scarce. Leu-7+ cells predominated within the neoplastic nodules in 5 cases. With the anti-dendritic reticulum cell monoclonal antibody, all 17 cases showed a network, usually more loosely arranged than in reactive follicles. In 4 cases, of follicular and diffuse lymphoma, this network was extremely dissociated and in some areas these cells were scanty or lacking. We concluded that immunoperoxidase on frozen sections, using monoclonal antibodies, appears to be the most reliable method for the immunological phenotyping of follicular lymphomas.