An immortalized cell line with features of human follicular dendritic cells. Antigen and cytokine expression analysis

Follicular dendritic cells (FDC) are specialized cells residing primarily within lymphoid follicles. They bind immunocomplexes and play an important role in the presentation of antigen to follicular B cells. Isolation of FDC for in vitro studies, however, is difficult because they constitute only about 1% of the cells in lymphoid tissue and form tight clusters entrapping lymphocytes within their dendritic processes. The monoclonal antibody (mAb) Ki-M4, which is highly restricted in its binding to FDC, is used to identify these cells. In order to establish a new immortalized cell line with features of FDC, we applied a modified procedure to isolate and enrich FDC from human tonsils and fused them with the myeloma cell line SP2/0-Ag14. The new hybrid cell line, designated FDC-H1, is of both mouse lymphoid and human FDC origin. FDC-H1 was found to have unlimited growth potential and to consistently express the Ki-M4 antigen and other surface antigens of human FDC. Semiquantitative reverse-transcribed polymerase chain reaction (RT-PCR) of enriched FDC and FDC-H1 revealed the same highly restricted cytokine/mRNA profile for both, with detectable levels of interleukin (IL)-1 alpha and surface CD23 and a lack of mRNA for IL-1 beta, IL-2, IL-3, IL-4, IL-7, IL-9, IL-10, interferon-gamma, tumor necrosis factor-alpha, transforming growth factor-beta and granulocyte/macrophage-colony-stimulating factor. Additionally a weak but constant IL-6 mRNA expression was found in the cell line FDC-H1 by RT-PCR. In situ hybridization experiments in tonsils revealed IL-6 transcripts in cells with a staining pattern characteristic of a dendritic cell only in a few germinal centers. To our knowledge, FDC-H1 is the first cell line that constantly expresses surface antigens and a cytokine profile characteristic of FDC. It is, therefore, well suited for studying the biology of FDC and the functional relationship between FDC and normal or neoplastic lymphatic cells.