Immunohistochemical analysis of progressively transformed follicular centers

Using an in situ immunohistochemical technic and a panel of monoclonal antibodies directed to lymphocytes, dendritic reticulum cells, HLA-DR antigen and killer/natural killer cells, the cellular composition of progressively transformed follicular centers (PTFCs) was analyzed. PTFCs are large lymphoid aggregates, composed of BA1+B1+sIgM+sIgD+ small B-lymphocytes, admixed with randomly arranged OKT4+Leu-3a+ helper/inducer T-cells and Leu-7+ cells. Small islands of B1+BA1-sIgD- follicular center cells are present in the central part of PTFCs, but fail to form a true follicular center. DRC1+ dendritic reticulum cells are arranged abnormally, forming small, separate clusters or a loosely arranged network lacking the typical concentric pattern. Moreover, dendritic reticulum cells have less extensively developed cytoplasmic extensions and are devoid of surface-bound immunoglobulins. Based on these findings, it is suggested that blastic transformation of B-cells in PTFCs is incomplete. The occurrence of PTFCs among numerous well-formed, secondary lymphoid follicles, and their exclusive association with exaggerated follicle formation speaks against an intrinsic inability of dendritic reticulum cells to bind antigen-antibody complexes, but rather suggests that PTFCs represent early, transient stages in the transformation of primary into secondary lymphoid follicles.