SPARC对脾脏边缘带B细胞功能的调节作用及机理研究

Extracellular matrix (ECM) is involved in the regulation of development and differentiation of B cells. SPARC, a component of ECM, regulates cell proliferation, differentiation, apoptosis, adhesion and migration, via directly affecting cells, or indirectly affecting the interactions between cells and cells, cells and ECM, or cells and growth factors. Our previous study showed that SPARC regulated the development of progenitor B cells through affecting the microenvironment in bone marrow. Further investigation showed that in SPARC-deficient mice, the volume of spleen as well as the number of neutrophils in spleen was increased, with increased number of B cells and elevated levels of IgG and IgM in blood. It has been demonstrated that neutrophils in spleen could promote B cell proliferation and differentiation by presenting antigen and secreting B-related factors. Moreover, neutropenic patients had fewer and hypomutated marginal zone (MZ) B cells and less preimmune immunoglobulins. Accordingly, whether abnormalities exist in SPARC-null spleen MZB cells？And are these abnormalities associated with spleen neutrophils？ This project intends to explore the relationship between MZB and neutrophils in spleen, and the mechanism by which neutrophils affect MZB function, by using the SPARC-null mice model. Implementation of this project will help reveal novel mechanisms by which ECM regulates humoral immunity.

细胞外基质可调节B细胞的发育和分化。SPARC是细胞外基质成分，通过直接作用于细胞，或影响细胞与细胞、细胞与细胞外基质、细胞与生长因子之间的相互作用，调节细胞的增殖、分化、凋亡、粘附和迁移。我们前期的研究表明，SPARC可通过影响骨髓微环境调节B细胞的发育；进一步研究发现，SPARC缺失小鼠脾脏体积明显增大，脾脏中性粒细胞数量增加，外周血B细胞频数增加，IgG和IgM水平增高。已知脾脏中性粒细胞能通过递呈抗原和分泌B细胞活化相关分子，激活B细胞的增殖和分化。中性粒细胞减少症患者外周血边缘带（marginal zone, MZ）B细胞、抗体水平和种类均明显减少。那么，SPARC缺失小鼠脾脏MZB是否存在异常？这种异常与脾脏中性粒细胞是否有关？本项目拟利用SPARC缺失小鼠，研究脾脏MZB与中性粒细胞的关系及中性粒细胞调节MZB的机理。本项目的实施将有助于揭示细胞外基质调节体液免疫的新机制。

富含半胱氨酸的酸性分泌蛋白SPARC是细胞外基质成分，通过直接作用于细胞，或影响细胞与细胞、细胞与细胞外基质、细胞与生长因子之间的相互作用，调节细胞的增殖、分化、凋亡、粘附和迁移。我们前期的研究发现，SPARC 缺失小鼠脾脏明显增大，脾脏中性粒细胞增多，血液中B细胞增加，血清IgG、IgM 水平显著升高，但其分子机制尚不清楚。因此，本项目拟采用细胞和分子生物学技术，研究了SPARC对脾脏组织结构和MZB细胞功能的影响；SPARC对脾脏中性粒细胞定位、数量、NET形成和功能的影响；中性粒细胞减少症患者血清免疫球蛋白水平与SPARC表达水平的相关性。我们的结果表明SPARC敲除小鼠比野生型小鼠具有更高的脾脏指数和MZB细胞比例。SPARC基因在LPS脓毒症小鼠模型中发挥关键的炎症反应保护作用。此外, SPARC敲除对小鼠的MZB和中性粒细胞功能产生显著影响。最后研究结果还阐明了脾脏MZB与中性粒细胞的关系及中性粒细胞调节MZB 的机理。通过本项目的实施不仅有助于阐明SPARC对脾脏边缘带B细胞和中性粒细胞功能的调节作用及机理，同时为揭示哺乳动物中细胞外基质调节体液免疫的新机制提供新思路。