STAT1是第一型與第二型干擾素訊息傳遞中的重要訊息調控分子，然而STAT1在體液免疫中扮演何種角色仍然未知。在此我們證明STAT1是調控體液免疫反應的重要分子。我們經實驗觀察發現STAT1基因剔除小鼠在受到T-dependent抗原TNP-OVA的刺激後其體液免疫反應出現嚴重的缺陷，這些包括TNP專一性抗體效價降低、同型抗體轉換(isotype switching)反應不全、濾泡生發中心( germinal center)數量減少，而且負責濾泡生發中心形成的BCL6基因表現量降低。此外刺激後的STAT1基因剔除小鼠的脾臟與骨髓中之TNP專一性漿細胞數目大量減少，有趣的是sXBP1而非Blimp1基因表現量有明顯降低。
為了更進一步探討STAT1調控體液免疫的可能機制，我們使用了T-dependent抗原進行的體外刺激。STAT1基因剔除小鼠的脾臟細胞和B淋巴球在受到抗CD40單株抗體與IL-4的刺激後，出現了細胞分裂能力降低與漿細胞分化不全之現象。經流式細胞儀分析結果顯示經刺激後表現CD138+與IgG+細胞數目有明顯的減少，而這些細胞中的Blimp1、sXBP1、AID等基因之表現量均有降低情形。綜合以上結果，我們發現在STAT1基因剔除老鼠體內與體外培養系統中均出現體液免疫反應缺陷，這些現象都顯示STAT1在B淋巴球分化過程中扮演重要的角色。

Signal transducer and activator of transcription (STAT) 1 is a critical signal mediator for type I and type II interferon. However, the role of STAT1 in humoral immunity remains unclear. Here, we demonstrate that STAT1 was required for humoral immune response. Severely impaired humoral immunity, including reduced titer of TNP-specific antibodies, impaired isotype switching, and decreased numbers of germinal center in the spleen were observed in STAT1KO mice in response to TNP-OVA, a T-dependent antigen. Interestingly, STAT1KO mice displayed reduced level of BCL6, which is important for germinal center formation. In addition, the TNP-specific plasma cells in the spleen and bone marrow of STAT1KO mice were significantly reduced after immunization. Coincidentally, we found that the level of sXBP-1, but not Blimp1 was reduced.
To further elucidate the underlying mechanisms, we did in vitro stimulation using T-dependent antigen. Splenocytes or purified B cells of STAT1KO mice treated with anti-CD40 plus IL-4 in vitro also showed reduced proliferation activity and plasma cell formation. Flow cytometric analysis showed that CD138 + cells and IgG1 + cells after stimulation were dramatically reduced in STAT1KO cells, which was consistent with reduced level of Blimp1, sXBP-1 and AID in these cells.
Taken together, the results from STAT1KO mice revealed defective humoral responses in vivo and in vitro, indicating that STAT1 plays an important role in B cell differentiation.