Antigenic phenotyping of human follicular dendritic cells isolated from nonmalignant and malignant lymphatic tissue

Follicular dendritic cells (FDC) are located within follicles of secondary lymphoid tissue and in lymph nodes of patients with germinal center cell-derived non-Hodgkin lymphomas. Reliable antigenic phenotyping of FDC within tissue sections has been difficult due to simultaneous labeling of the surrounding germinal center cells. Using an enzyme cocktail to digest human tonsils and cervical lymph nodes with subsequent fractionation by albumin gradient centrifugation, cell isolates containing up to 20% FDC were obtained. This preparation allowed the determination of antigenic phenotype on individual FDC. Molecules expressed by FDC were detected by an isotype-specific immunocytochemical double-labeling procedure, i.e. a monoclonal antibody (mAb) specific for FDC (KiM4 or DRC1) in conjunction with a mAb reactive against an additional antigenic determinant. Nonspecific binding of mAb to immunoglobulin Fc receptors located on FDC membranes was avoided by incubation of cells with human IgG aggregates prior to immunostaining. The results revealed that isolated FDC from these lymphoid tissues express transferrin receptors, the intercellular adhesion molecule 1, class II antigens, the B cell antigens CD20 and CD21, and the myelomonocytic properties CD11b and CD14. Immunoglobulin mu or gamma heavy chains and the B cell antigens CD23 and CD24 are detected on 50% of an isolated FDC population. These FDC are negative for the T helper cell antigen CD4, the B cell cell antigens CD19 and CD22, the immunolobulin alpha and delta chains and the S-100 protein. FDC isolated from lymph nodes of patients with low-grade malignant non-Hodgkin lymphoma, identified by DRC1 or KiM4 mAb, presented the same antigenic profile as seen on FDC from nonmalignant tissue. This suggests that FDC from lymphoma tissue isolated in this manner have the same properties as those found in normal tissue.