Follicular dendritic cells (FDCs) in the lymphoid follicle (LF) are essential to the sequential processes of B-cell proliferation, selection, and differentiation. Although the importance of some cytokines in these processes has been pointed out, there is little information about the follicular localization of their receptors. We investigated, with special reference to FDCs, the localization of cytokine receptors as well as cytokines themselves in human tonsils by several means, including immunochemistry, immunoelectron microscopy, reverse transcriptase polymerase chain reaction, and in situ hybridization. FDCs in the follicular apical light zone expressed transforming growth factor-β receptor II (TGF-βR II), granulocyte-macrophage colony-stimulating factor receptor α (GM-CSFRα; CDw116), tumor necrosis factor receptor I (TNFR I; CD120a), interleukin-1 receptor II (IL-1R II; CDw121b), IL-2 receptor β (IL-2Rβ; CD122), IL-4 receptor (IL-4R; CDw124), and IL-6 receptor (IL-6R; CD126), among the 10 receptors examined. Those in the basal light zone expressed strongly TNFR I and weakly GM-CSFR α, IL-1R II, IL-2Rβ, IL-4R, and IL-6R, and often those in the outer and mantle zones expressed GM-CSFR α, IL-4R, and IL-6R. FDCs in the apical light zone expressed only TGF-β among the 7 cytokines examined. On the other hand, follicular lymphocytes mainly in the light zone expressed 9 kinds of receptors, with the exception being TGF-βR II; expression was rather frequent for TNF-α, IL-1α, and IL-2 and less frequent for TGF-β, GM-CSF, IL-4, and IL-6. These data indicate that only FDCs mainly in the light zone express many cytokine receptors, although FDCs may produce the cytokine, TGF-β. Cytokines may act not only on some follicular lymphocytes but also on most FDCs in the light zone expressing cytokine receptors.
Isolated lymphoid follicle maturation induces the development of follicular dendritic cells
