Toll-like receptor (TLR)와 Nod-like receptor (NLR)는 특이적으로 보존된 병원체의 구조 (PAMP, pathogen-associated molecular pattern)를 인식하는 pattern-recognition receptor (PRR)이다. PRR은 주로 선천 면역 세포에서 발현되며, PRR-PAMP 결합은 선천 면역 및 적응 면역 반응을 유발한다. 몇몇 연구에서 B 세포도 TLR과 NLR를 발현하며, TLR과 NLR의 자극은 B 세포의 증식, 분화 및 면역글로불린 (Ig) class switch recombination (CSR)을 유도한다고 보고한 바 있다. 그러나 아직까지 B 세포 활성화 및 분화에 대한 TLR과 NLR의 역할에 대해서는 완전히 밝혀져 있지 않다. 따라서 본 연구에서는 TLR4 리간드인 LPS와 더불어 Nod2 리간드 MDP 및 TLR1/2 리간드 Pam3CSK4를 마우스 비장으로부터 순수 분리한 resting B 세포에 처리/자극한 후, B 세포의 증식, 생존 및 항체 생산을 in vitro 배양을 통하여 조사/분석하였다. MDP 단독 처리는 B 세포 생존을 유지시켰으며 IgM 생산을 약간 증가시켰다. 또한 MDP는 LPS와 협력하여 B 세포 증식 및 생존을 강화시켰다. 그러나 Nod1 리간드인 iE-DAP은 LPS-유도성 B 세포의 증식 및 생존에 영향을 주지 않았다. 또한 MDP는 LPS와 협력하여 germline (GL) ?2b transcripts (GLT?2b)의 발현을 증가시킴으로써 IgG2b의 생산을 증가시켰다. Nod2 및 TLR4 결핍 마우스 실험을 통해, 앞서 관찰한 B 세포 활성에 대한 MDP와 LPS의 협력 효과는 Nod2- 및 TLR4-의존적 반응이라는 것을 알 수 있었다. 한편, MDP와 LPS에 의한 B 세포의 증식은 RIP2/p38과 JNK 경로를 통해 유도되지만, 이들 경로는 GLT?2b의 발현에는 영향을 주지 않았다. Pam3CSK4는 B 세포의 성장 및 증식을 증가시킨 반면, 항체 중 IgG1 생산만을 농도 의존적으로 저해하였다. 또한 Pam3CSK4는 LPS-유도성 B 세포의 증식 및 생산을 증가시켰다. 흥미롭게도, Pam3CSK4는 LPS-유도성 IgG1 및 IgG3생산은 저해하는 반면, LPS 유도성 IgG2a의 생산은 강화시켰다. 게다가 Pam3CSK4는 LPS-유도성 GLT?1의 발현을 저해하는 반면, LPS 유도성 GLT?2a의 발현은 증가시켰다. 한편, Pam3CSK4는 LPS-유도성 형질세포 분화에는 영향을 주지 않았다. 사이토카인 (IL-4, IFN-?) 및 비장 전체 세포 배양 실험에서도 Pam3CSK4는 LPS에 의해 유도된 IgG1 및 IgG3 생산을 억제하였으며, LPS-유도성 IgG2a 생산은 강화시켰다. 결론적으로, 본 연구에서는, Nod2와 TLR4 신호전달자극은 상호 협력함으로써 RIP2/p38과 JNK 경로를 통하여 B 세포 증식을 증강시키며, 상호 협력을 통하여 GLT?2b 발현을 증가시킴으로써 IgG2b의 생산을 강화함을 알 수 있었다. 한편, TLR1/2 리간드 Pam3CSK4는 강력한 B 세포 마이토젠으로 작용하며 TLR4 리간드 LPS와 협력하여 B 세포의 증식을 증가시키지만, 이들 두 개의 서로 다른 TLR 리간드들은 각각의 항체 동형 (특히 IgG1과 IgG2a)에 대한 Ig CSR을 조절함에 있어서 다양한 역할을 한다는 것을 알 수 있었다. 이와 같이, 두 개의 PRR 리간드 MDP와 Pam3CSK4는 LPS와 더불어 T 세포의 도움이나 BCR 자극 없이 직접적으로 B 세포 활성을 증강시킬 수 있으며 특정 항체 생산을 선택적으로 강화시키거나 억제시킬 수 있다 (MDP, IgG2b↑; Pam3CSK4, IgG2a↑? IgG1↓). 따라서, MDP와 Pam3CSK4는 효과적인 B 세포 면역활성 보조제로 개발될 수 있다.
Toll-like receptors (TLRs) and Nod-like receptors (NLRs) are pattern-recognition receptors (PRRs) that recognize specific conserved microbial structure (PAMPs, pathogen-associated molecular patterns). PRRs are mainly expressed in innate immune cells and PRR-PAMP interaction triggers innate and adaptive immune responses. Several studies have reported that B cells also express both TLRs and NLRs, and the receptors signaling contribute to B cell proliferation, differentiation, and immunoglobulin (Ig) class switch recombination (CSR). However, the roles of TLRs and NLRs in B cell activation and differentiation are not fully understood. In this study, we investigated the effects of Nod2 agonist MDP and TLR1/2 agonist Pam3CSK4 in combination with/without TLR4 agonist LPS on B cell proliferation, viability, and antibody production in vitro culture of purified mouse spleen resting B cells. MDP alone sustained B cell viability and slightly induced IgM production. In addition, MDP, but not Nod1 agonist iE-DAP, cooperates with LPS to induce B cell proliferation and viability. Furthermore, MDP and LPS synergistically increased IgG2b production through enhancing germline (GL) ?2b transcripts (GLT?2b) expression. In the experiment of Nod2- and TLR4-deficient mice, we found that the cooperative effect of MDP and LPS is dependent on the receptors, Nod2 and TLR4. On the other hand, LPS/MDP-induced B cell proliferation was mediated by JNK and RIP2/p38 pathway, but these pathways did not affect GLT?2b expression. Pam3CSK4 increased B cell proliferation and viability, while it inhibits IgG1 production in a dose-dependent manner. Pam3CSK4 additively increased LPS-induced B cell proliferation and viability. However, interestingly enough, Pam3CSK4 inhibited LPS-induced IgG1 and IgG3 production, while it increased LPS-induced IgG2a production. Furthermore, Pam3CSK4 inhibited LPS-induced GLT?1, but not GLT?3, expression, whereas it enhanced LPS-induced GLT?2a expression. On the other hand, Pam3CSK4 did not affect LPS-induced plasma cell differentiation. We also observed that, in the presence of cytokines (IL-4 and IFN-?) and in total spleen cells, Pam3CSK4 diminished LPS-induced IgG1 and IgG3 production but enhanced LPS-induced IgG2a. In conclusion, our present study suggests that cross-talk between Nod2 and TLR4 signaling enhances B cell proliferation via RIP2/p38 and JNK pathways and specifically increases IgG2b production through increasing GLT?2b expression. TLR1/2 agonist Pam3CSK4 can act as a potent B cell mitogen and cooperates with TLR4 agonists LPS to induce B cell growth, but these two different TLR agonists play diverse roles in regulating the Ig CSR of each isotype (e.g., IgG1 and IgG2a). Thus, two PRR agonists, MDP and Pam3CSK4, in combination with LPS directly enhance B cell activation and selectively reinforce or suppress Abs production (i.e., MDP, IgG2b↑; Pam3CSK4, IgG2a↑ ? IgG1↓) independent of T cells and B cell receptor (BCR) stimulation, and thereby MDP and Pam3CSK4 can be developed as effective B cell adjuvants.
LIST OF FIGURES ivLIST OF TABLES viiABBREVIATIONS viiiI. INTRODUCTION 11. B cell development, activation, and differentiation 12. Mechanism of class switch recombination 33. Toll-like receptors 54. Nod1 and Nod2 55. The roles of TLR and NLR in B cells 76. Purpose of the study 8II. MATERIALS AND METHODS 101. Animals 102. Cell culture and reagents 103. Cell viability assay 124. CFSE analysis 145. Isotype-specific ELISA 146. Cell surface analysis 147. RNA isolation and RT-PCR 158. Construction of germline ?2b promoter reporter plasmids 159. Transfection and luciferase assay 19III. RESULTS 201. Screening of TLR and NLR agonists for B cell proliferation and antibody production 201-1. Expression of TLRs and NLRs in mouse spleen B cells 201-2. Effects of TLR and NLR agonists on B cell proliferation and antibody production 202. Effects of TLR4 agonist LPS and Nod2 agonist MDP on B cell growth and antibody production 252-1. Dosage effect of MDP on B cell viability and proliferation 252-2. Nod2 agonist MDP, but not Nod1 agonist iE-DAP, cooperates with TLR4 agonist LPS to induce B cell viability, proliferation, and IgG2b production 252-3. MDP cooperates with LPS to induce germline 2b transcripts 292-4. Combination effect of LPS and MDP is abrogated in TLR4- and Nod2-deficient B cells 292-5. Effects of MAPK inhibitors on LPS and MDP-induced B cell viability, proliferation, and antibody production 312-6. Effects of LPS and MDP on germline 2b promoter activity 373. Effects of TLR1/2 agonist Pam3CSK4 and TLR4 agonist LPS on B cell growth and antibody production 423-1. Effect of Pam3CSK4 or LPS on B cell proliferation and antibody production 423-2. Dosage effect of Pam3CSK4 on B cell proliferation, viability, and antibody production 423-3. Dosage effect of LPS on B cell proliferation, viability, and antibody production 453-4. Combination effect of Pam3CSK4 and LPS on B cell proliferation, viability, and antibody production 453-5. Effects of Pam3CSK4 and LPS on germline transcripts and AID mRNA expression 483-6. Kinetic effect of Pam3CSK4 and LPS on B cell growth, germline transcripts expression and antibody production 483-7. Dosage effect of Pam3CSK4 on LPS-induced B cell growth and antibody production 523-8. Pam3CSK4 dose not affect LPS-induced plasma cell differentiation 553-9. Effects of cytokines on Pam3CSK4 and LPS-induced antibody production 553-10. Effects of Pam3CSK4 and LPS on antibody production by total spleen B cells 57IV. DISCUSSION 601. Effects of TLR4 agonist LPS and Nod2 agonist MDP for B cell growth and antibody production: ‘LPS/MDP study’ 602. Effects of TLR1/2 agonist Pam3CSK4 and TLR4 agonist LPS on B cell growth and antibody production: ‘Pam3CSK4/LPS study’ 62V. REFERENCES 68VI. ABSTRACT 75VII. 국문 요약 77