- 學位論文
傳統樹突細胞亞群的差異影響胸腺非依賴性 B 細胞的反應
Differential Effects of Conventional Dendritic Cell Subsets on Enhancing T-independent B cell Response
摘要
B細胞可以藉由胸腺依賴性或非依賴性的途徑活化。在缺乏胸腺細胞（主要是T細胞）幫助的情況下，B細胞會接收其他細胞提供的訊號促進胸腺非依賴性反應。過去研究已知漿狀樹突細胞(plasmacytoid dendritic cell, pDC)在經由類鐸受體 (Toll-like receptor, TLR) 刺激時可以產生大量的第一型干擾素(type I interferon, IFN-I)，並且藉由IFN-I促進B細胞的胸腺非依賴性反應。然而傳統樹突細胞 (conventional dendritic cell, cDC) 在其中所扮演的角色仍不明確。我們的研究發現cDC可以藉由胸腺非依賴性的方式促進B細胞反應。當B細胞和骨髓所分化的傳統樹突細胞 (bone marrow-derived cDC, BM-cDC) 共同培養並且以CpG (TLR9配體) 刺激時，除了細胞增殖外，其活化、分化以及細胞激素產量相較B細胞單獨培養都有顯著的提升。有趣的是，cDC可以在缺乏IFN-I訊號的情況下促進B細胞活化，代表cDC可以藉由IFN-I以外的訊號幫助B細胞。然而，與B細胞相反，在兩種細胞共同培養時cDC的功能卻會受到抑制，其活化和細胞激素產量會下降。除此之外，我們發現雖然cDC1和cDC2都可以促進B細胞反應，但兩者對於FO B和MZ B細胞(兩個B細胞亞群)的調控有所不同。cDC1傾向於促進MZ B細胞活化，而cDC2則傾向促進FO B細胞活化。另外，cDC1主要藉由細胞與細胞接觸方式調控B細胞反應，而cDC2相較於cDC1會產出較多促發炎性的細胞激素，但其產量卻會受到FO B和MZ B抑制。相反的，當cDC1和MZ B共同培養時，有些細胞激素的分泌 (例如：IFN-I、IL-1、細胞趨化因子和IL-10則會上升。在體外培養系統中，當受到Streptococcus pneumoniae (S. pneumoniae) 刺激時，cDC也可以促進FO B或MZ B細胞活化。此外，在活體動物實驗中，小鼠受到S. pneumoniae刺激後脾臟中的cDC1會遷移到邊緣區 (marginal zone)，並且和MZ B細胞接觸。總而言之，我們證實在TLR9刺激下，cDC可以促進B細胞反應。另外，在受到病原體感染時，cDC1和MZ B細胞間有較強的協同作用反應，這可能在感染初期的免疫反應中扮演重要角色。
並列摘要
B cells can be activated through either T-dependent (TD) or T-independent (TI) pathways. In the absence of T cell help, B cells may use various signals to facilitate their TI response. While plasmacytoid dendritic cells (pDCs) are known to enhance B cells activation in response to TLR stimulation by secreting large amounts of type I interferons (IFN-I), the role of conventional DCs (cDCs) remains largely unclear. Here, we showed that cDCs could also enhance B cell response in a T-independent manner. Following the coculture of B cells with BM-derived cDCs and the treatment of CpG, a TLR9 agonist, activation, cytokine production and differentiation were significantly increased compared to B cell alone. However, there was no significant change in proliferation of B cells. Interestingly, cDCs were able to promote B cells activation even in the absence of IFN-I pathways, suggesting that cDCs may cooperate with B cells through an IFN-I-independent manner. In contrast to B cells, the functions of cDCs were negatively impacted, with reduced expression of costimulatory molecules, activation markers and cytokine production following the coculture with B cells. Furthermore, we found that although both cDC1s and cDC2s could enhance B cells response, they had differential potency and mechanisms to assist follicular B (FO B) and marginal zone B (MZ B), two different subsets of B cells. cDC1s and cDC2s selectively enhanced the response of MZ B and FO B cells, respectively. Moreover, the effect of cDC1s was more dependent on cell-to-cell contact, which was greatly attenuated in the transwell system. cDC2s produced more inflammatory cytokines, including IFN-I, than did cDC1s, which was negatively regulated by both FO B and MZ B. In contrast, production of cytokines, including IFN-a, IL-1b, chemokines and IL-10 was elevated when cDC1s cocultured with MZ B cells. In addition to CpG, cDCs also enhanced the activation of FO B and MZ B cells in response to Streptococcus pneumoniae stimulation in vitro. Moreover, cDC1s migrated into marginal zone and interacted with MZ B cells after the mice were intravenously immunized with Streptococcus pneumoniae in vivo. Together, we demonstrated that cDCs can significantly enhance B cells response under CpG stimulation, through different pathways to that of pDCs. In addition, preferential interactions between cDC1s and MZ B cells in response to pathogen infection may be critical for early immune response.