THE HUMAN GERMINAL CENTER CELLS, FOLLICULAR DENDRITIC CELLS AND GERMINAL CENTER T-CELLS PRODUCE B-CELL-STIMULATING CYTOKINES

Cytokine gene expression was investigated in the germinal centre const ituents of follicular dendritic cells and germinal centre T cells and compared to the mRNA expression of nongerminal centre tonsillar cells. Cells were isolated from human tonsils by preenrichment with MACS and subsequent FACS sorting. Cytokine gene expression was investigated by intron-spanning RT-PCR for IL-1 alpha, IL-1 beta, IL-2, IL-4, IL-5, I L-6, IL-10, IFN-alpha, IFN-beta, IFN-gamma, and TNF-a. Frequency of cy tokine-producing cells and the cytokine production pattern of single c ells were determined by single cell PCR. Furthermore, cytokine protein expression was investigated by immunohistology. Using these methods, we found a strong production of IL-1 beta mRNA and protein in a small percentage of FDC. Germinal centre T cells showed production of IL-2, IL-4, IL-10, IFN-gamma, and TNF-alpha mRNA. The mRNAs of these cytokin es could also be detected at the single cell level; as they were produ ced in a high percentage of germinal centre T cells, whereas immunohis tological staining was negative, we conclude that a high percentage of germinal centre T lymphocytes produce IL-2, IL-4, IL-10, IFN-gamma an d TNF-alpha in low concentrations in contrast to T cells outside the g erminal centre, in which strong cytokine production in few cells was s hown earlier.