Immunophenotypic characterization of primary and secondary lymphoid follicles.

The need for an immunophenotypical referential framework relative to lymphoid follicle has led us to apply a panel of monoclonal and polyclonal antibodies, by means of a sensitive immunostaining method. Lymphoid follicle is an immunophenotypically complex structure made up of three lymphoid populations (B, being its bulk, and a few T and NK cells), dendritic reticulum cells (DRCs) and Flemming's macrophages. Follicular B population is To 15 +, B1+, OKB 7 +, HLA-DR + and C3bR +. In secondary follicles there are differential characteristic reactivities for each topographic compartment: Mantle zone is positive for OKB 2 and surface IgM (sIgM) and IgD (sIgD); germinal center (GC) clear zone (with centrocytic predominance) for OKT 9, sIgM and weakly for OKB 2; and GC dark zone (with centroblastic predominance) only for OKT 9. In sections, OKT 10 allows one to see immunoblasts and plasma cells, the latter being with lymphoplasmacytoid cells the only intracytoplasmic immunoglobulin holders. 10% of GC lymphocytes are T cells, almost exclusively T-helper (Leu 3a +). Another 10% to 15% of lymphoid cells are Leu 7 (HNK-1) +. In histological sections, DRCs are specifically marked with R4/23 and Flemming's macrophages with anti-alpha1-antitrypsin and anti-alpha1-antichymotrypsin antibodies, both populations being negative to OKM 1 and OKM 5.