Regulation of the Immune Response to Polysaccharides and

摘要：多糖类抗原的免疫应答受高度调控，具有亚类受限、基因使用可变区、特异性好和亲和力强等特点。未与蛋白质结合的简单PS(如细菌Levan、BL和脑膜炎奈瑟氏菌C群，MCPS)可引起胸腺非依赖性(TI)反应。另一方面，PS与蛋白质(如与破伤风类毒素偶联的MCPS-TT)结合后，会引起一种不同类型的反应，称为胸腺依赖(TD)。我们先前分析了抗BL抗体，并展示了芳香族和碱性氨基酸在抗PS抗体CDRs中的重要性。我们对抗In反应多样性调节的分析将SR1多样性基因定位在小鼠14号染色体上。最近在TCR KO小鼠中的研究表明，尽管血清中的IgG和IgM显著增加，但对In的反应不仅是TI，而且不受T细胞的影响。以往对抗MCPS和抗MCPS TT mAb的分析表明，VH基因家族在TI和TD反应中的使用是由VHJ558控制的。与抗BL抗体一致，模拟研究也表明碱性氨基酸在结合时的相关性与亲和力的增加。对商业结合疫苗免疫的小鼠和固定N-脑膜炎疫苗免疫的小鼠的Biaccore分析表明，结合疫苗PS部分的O-乙酰化状态决定了抗PS抗体的相对特异性。与固定细菌免疫相比，结合疫苗可激发更强的免疫球蛋白反应，包括对OAC+和OAC-PS的抗体。此外，这些偶联物诱导的相对亲和力更高，对OAc+或OAc-的反应性相当，或对OAc-的反应性更高。我们早期的研究表明，新生儿树突状细胞呈递破伤风类毒素(TT)和淋球菌C群多糖-破伤风类毒素结合物(MCPS-TT)的功能受损，这可能是新生儿未能产生成人样的抗MCPS抗体反应的机制之一。因此，进一步研究树突状细胞是否能够直接调节B细胞的功能。从MCPS-TT免疫的小鼠分离的树突状细胞在体外诱导了显著的抗原特异性B细胞增殖。在从同一小鼠分离的T细胞存在的情况下，培养抗原诱导的B细胞也能导致B细胞的增殖。在免疫B细胞和T细胞培养中加入树突状细胞后，B细胞的增殖更为旺盛。然而，从新生小鼠分离的树突状细胞在有或没有成人免疫T细胞的情况下都不能对B细胞的增殖起到这样的作用。这些结果表明，树突状细胞除了激活幼稚T细胞外，还在调节B细胞的生长和反应中发挥重要作用，但这种作用在新生儿树突状细胞中是有缺陷的。此外，与成人树突状细胞不同，新生小鼠的树突状细胞在体外不能诱导TT或MCPS-TT诱导的T细胞分泌IL-2和干扰素-g。MCPS可诱导树突状细胞分泌IL-6，新生儿树突状细胞产生的IL-6水平明显低于对照组。在另一项研究中，来自MCPS-TT免疫小鼠的T细胞克隆的特征表明，多糖反应性T细胞克隆需要抗原提呈细胞接触，但不受MHC限制。儿童疫苗倡议的目标之一是减少为儿童充分接种疫苗所需的接触人数。为了实现这一目标，已经对几种组合疫苗进行了安全性和婴儿免疫原性测试。我们已经开发了一个模型，用于研究联合疫苗对单个成分的反应的影响。分别和混合注射不同组合的Hib-TT、DTaP和IPV，并将它们对不同抗原的抗体应答与只接种这三种疫苗中的一种的小鼠进行比较，所有含Hib的疫苗与IPV混合或在另一地点同时接种，抗脊髓灰质炎效价比单独注射IPV降低，且抗I型疫苗的差异大于类型2和3型。抗I型疫苗效价差异显著。MCPS-TT和IPV的类似组合也没有导致抗脊髓灰质炎反应减弱。

Summary: The immune response to polysaccharide (PS) antigens is highly regulated and has several distinguishing features including restricted subclass, variable region gene usage, fine specificity, and avidity. Simple PS not conjugated to protein (such as bacterial Levan, BL and Neisseria meningitidis group C, MCPS) elicit a thymus-independent (TI) response. PS conjugated to proteins (such as MCPS coupled to tetanus toxoid, (MCPS-TT)), on the other hand, elicit a different type of response, termed thymus-dependent (TD). We previously analyzed anti-BL antibodies and showed the importance of aromatic and basic amino acids in the CDRs of anti-PS antibodies. Our analysis of the regulation of diversity in the anti-In response mapped the Sr1 diversity gene to mouse chromosome 14. Recent studies in TCR KO mice have shown that the response to In is not only TI, but is not influenced by T cells when added back, despite a large increase in serum IgG and IgM. Previous analyses of anti-MCPS and anti-MCPS TT mAb reveal that VH gene family usage in both the TI and TD response is dominated by VHJ558. Consistent with anti-BL Abs, modeling studies also suggest a correlation of basic amino acids in the combining with an increase in affinity. BIAcore analysis of mice immunized with commercial conjugate vaccines compared with mice immunized with fixed N. meningitides showed the O-acetylation status of the PS moiety of conjugate vaccines determines the relative specificity of anti-PS Abs. Compared to immunization with fixed bacteria, the conjugate vaccines elicit a greater IgG response including antibodies to both OAc+ and OAc- PS. Furthermore, the conjugates induce higher relative avidity IgG Abs of either equal reactivity on OAc+ or OAc- or higher OAc- reactivity. Our earlier studies showed that neonatal dendritic cells are functionally impaired in their ability to present tetanus toxoid (TT) and meingococcal group C polysaccharide-tetanus toxoid conjugate (MCPS-TT) to specific T cells suggesting it could be one of the mechanisms why neonates failed to make adult-like anti-MCPS antibody responses. Therefore, studies were undertaken further to understand whether or not dendritic cells are capable of regulating the function of B cells directly. Dendritic cells isolated from MCPS-TT primed mice induced significant antigen specific proliferation of B cells in vitro. Culturing antigen primed B cells in the presence of T cells isolated from the same mice also resulted in the proliferation of B cells. The addition of dendritic cells into the immune B and T cell culture caused more robust proliferation of B cells. However, dendritic cells isolated from neonatal mice failed to have such an effect on B cell proliferation either in the presence or absence of adult immune T cells. These results suggest that dendritic cells play an important role in regulating B cell growth and responses apart from their ability to activate naive T cells, and such effect is defective in neonatal dendritic cells. Also unlike adult dendritic cells, dendritic cells from neonatal mice failed to induce IL-2 and IFN-g secretion from TT or MCPS-TT primed T cells in vitro. MCPS was found to induce IL-6 secretion from dendritic cells and the level of IL-6 produced by neonatal dendrtic cells is significantly less. In another study, characterization of T cells clones derived from MCPS-TT immunized mice revealed that polysaccharide-reactive T cell clones require antigen presenting cell contact but are not MHC restricted. One of the goals of the Children's Vaccine Initiative is to reduce the number of contacts required to immunize a child fully. To meet this goal several combined vaccines have been tested for their safety and immunogenicity in infants. We have developed a model in SW outbred mice to examine the effects of combining vaccines on the response to individual components. Groups of mice were given different combinations of Hib-TT, DTaP and IPV, in separate and mixed injections, and compared their antibody responses to different antigens to those of mice who received only a single one of these three vaccines For all Hib-containing vaccines mixed with IPV or given simultaneously in another site, anti-polio titers were reduced compared to IPV alone and the differences were greater for anti-type 1 than types 2 and 3. The differences for anti-type 1 titers were significant. Similar combinations of MCPS-TT and IPV did nor result in a diminished ant-polio response.