[Immunoperoxidase study of normal and pathologic lymphoid tissue. Value of monoclonal antibodies]

Immunoperoxidase study can be performed either on fixed and paraffin embedded biopsy specimens or on frozen sections. Advantages and limits of these two methods, as well as the results obtained on normal and pathologic lymphoid tissue are presented. Immunoperoxidase on paraffin sections (PAP technic) is a simple method which allows a good morphologic analysis. However, most of the fixatives destroy proteic antigens particularly those linked to the cell membrane. Thus surface immunoglobulins (S.Ig) cannot be detected. In contrast cytoplasmic immunoglobulins remain antigenic enough to be demonstrated in routine paraffin embedded sections. In lymphomas synthesizing monotypic immunoglobulins, the percentage of labelled cells varies from 5 to 80%. Beside the background staining, which can be attenuated by trypsinisation, absorption of extracellular substances is often responsible for a false positive staining. Pathologists are mainly confronted with the passive uptake of extracellular immunoglobulins (IgG K and IgG L), as well as other serum proteins (lysozyme etc...). Immunoperoxidase on frozen sections allows the use of monoclonal antibodies. A large number of surface and cytoplasmic antigens can be detected. First, the localization of B and T lymphocytes, NK cells, interdigitating cells and dendritic reticulum cells within the normal lymph node is described. In the second part, the interest of monoclonal antibodies in differential diagnosis between lymphoma and pseudo-lymphoma, and in phenotyping of lymphomas is discussed. Now, it is possible to perform an in situ immunologic characterization of most lymphomas. B cell lymphomas have sIg associated with other antigens (Pan B+, HLA-DR+). Cells of chronic lymphoid leukaemia and centrocytic (cleaved-cell) lymphomas frequently express T65 (T 101+ or Leu 1+) antigen which is usually found on normal or neoplastic T lymphocytes. Monoclonal antibodies provide new evidence of the germinal centre origin of follicular lymphomas. Thus, monoclonal antibody directed against dentritic reticulum cells (CRD) revealed the same network of DRC in follicular lymphomas as in reactive germinal centres. This finding could account for the nodular pattern of these lymphomas, neoplastic cells being in some way, enclosed within the DRC network. On the other hand, neoplastic follicles are surrounded by a large amount of t lymphocytes. Some T lymphocytes are also found within the follicles where they are associated with NK cells. Lastly, as reactive benign follicles, neoplastic follicles are labelled by the anti-Calla antibody.(ABSTRACT TRUNCATED AT 400 WORDS)