IN-VITRO CULTURED STROMAL CELLS FROM HUMAN TONSILS DISPLAY A DISTINCTPHENOTYPE AND INDUCE B-CELL ADHESION AND PROLIFERATION

Peripheral lymphoid tissues contain a fibroblastic cell type referred to as stromal cells or reticulum cells which interact with lymphocytes as part of the lymphoid microenvironment. After isolation from human tonsils and expansion in vitro we analyzed the surface phenotype, extr acellular matrix components, cytoskeletal products, cytokine productio n, binding and functional interaction with B lymphocytes of in vitro c ultured stromal cells (HTSC) both in resting condition and after activ ation with tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamm a. Our results show that HTSC do not express specific myeloid, lymphoi d, endothelial or epithelial markers. HTSC express CD54 (ICAM-1), CD49 a (VLA-1). CD49b (VLA-2), CD49c (VLA-3), CD49e (VLA-5), CD49f (VLA-6), CD29, CD51, CD44 and produce vinculin, beta-tubulin, alpha-actin, vim entin, fibronectin, laminin and collagen types I, III and IV. Activati on of HTSC up-regulated CD54 (ICAM-1) and induced HLA-DR and CD106 (VC AM-1). HTSC constitutively produce interleukin (IL)-6 which is enhance d upon activation with TNF-alpha. IL-8 and granulocyte/macrophage colo ny-stimulating factor are detected only in the supernatants of activat ed HTSC. Reverse transcriptase polymerase chain reaction analysis reve aled that HTSC display mRNA for IL-1 alpha, leukemia inhibitory factor and IL-7. The adhesion of tonsillar B lymphocytes to activated HTSC i s mediated by CD11a/CD18 and CD54. Furthermore. HTSC can induce maxima l proliferation of IL-2-activated B lymphocytes cocultured in direct c ell-cell contact with HTSC. These results clearly distinguish in vitro cultured HTSC from common fibroblasts and other non-lymphoid elements present in the lymphoid parenchyma, such as follicular dendritic cell s, and show that HTSC actively participate in the lymphoid microenviro nment. In vitro cultures of HTSC could therefore be a useful model sys tem for detailed analysis of the interactions between stromal cells an d lymphocytes under physiological and pathological conditions.