El Shikh Mohey Eldin M, El Sayed Rania M, Wu Yongzhong, Szakal Andras K, Tew John G
Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA 23298, USA.
J Immunol. 2007 Oct 1;179(7):4444-50. doi: 10.4049/jimmunol.179.7.4444.
Microbial molecular patterns engage TLRs and activate dendritic cells and other accessory cells. Follicular dendritic cells (FDCs) exist in resting and activated states, but are activated in germinal centers, where they provide accessory function. We reasoned that FDCs might express TLRs and that engagement might activate FDCs by up-regulating molecules important for accessory activity. To test this hypothesis, TLR4 expression on FDCs was studied in situ with immunohistochemistry, followed by flow cytometry and RT-PCR analysis. TLR4 was expressed on FDC reticula in situ, and flow cytometry indicated that TLR4 was expressed on surface membranes and TLR4 message was readily apparent in FDCs by RT-PCR. Injecting mice or treating purified FDCs with LPS up-regulated molecules important for accessory activity including, FDC-Fc gammaRIIB, FDC-ICAM-1, and FDC-VCAM-1. Treatment of purified FDCs with LPS also induced intracellular phospho-IkappaB-alpha, indicating NF-kappaB activation, and that correlated with increased Fc gammaRIIB, ICAM-1, and VCAM-1. FDCs in C3H/HeJ mice were not activated with LPS even when mice were reconstituted with C3H/HeN leukocytes, suggesting that engagement of FDC-TLR4 is necessary for activation. Moreover, activated FDCs exhibited increased accessory activity in anti-OVA recall responses in vitro, and the FDC number could be reduced 4-fold if they were activated. In short, we report expression of TLR4 on FDCs for the first time and that engagement of FDC-TLR4 activated NF-kappaB, up-regulated expression of molecules important in FDC accessory function, including Fc gammaRIIB, ICAM-1, and VCAM-1, as well as FDC accessory activity in promoting recall IgG responses.
微生物分子模式可与Toll样受体（TLR）结合并激活树突状细胞和其他辅助细胞。滤泡树突状细胞（FDC）以静止和激活状态存在，但在生发中心被激活，在生发中心发挥辅助功能。我们推测FDC可能表达TLR，且这种结合可能通过上调对辅助活性重要的分子来激活FDC。为验证这一假设，采用免疫组织化学原位研究FDC上TLR4的表达，随后进行流式细胞术和逆转录聚合酶链反应（RT-PCR）分析。原位观察发现FDC网中有TLR4表达，流式细胞术表明TLR4表达于表面膜上，RT-PCR显示FDC中TLR4信息明显。用脂多糖（LPS）注射小鼠或处理纯化的FDC可上调对辅助活性重要的分子，包括FDC-FcγRIIB、FDC-细胞间黏附分子-1（ICAM-1）和FDC-血管细胞黏附分子-1（VCAM-1）。用LPS处理纯化的FDC还可诱导细胞内磷酸化核因子κB抑制蛋白α（phospho-IκB-α），表明核因子κB（NF-κB）激活，且这与FcγRIIB、ICAM-1和VCAM-1增加相关。C3H/HeJ小鼠的FDC即使在用C3H/HeN白细胞重建后也不能被LPS激活，提示FDC-TLR4的结合是激活所必需的。此外，激活的FDC在体外抗卵清蛋白（OVA）回忆反应中表现出增强的辅助活性，且如果FDC被激活，其数量可减少4倍。简而言之，我们首次报道了FDC上TLR4的表达，且FDC-TLR4的结合激活了NF-κB，上调了对FDC辅助功能重要的分子表达，包括FcγRIIB、ICAM-1和VCAM-1，以及FDC在促进回忆性IgG反应中的辅助活性。
