Role of Protective and Pathogenic B cells in Modulating Pediatric Severe Malaria

描述(申请人提供)：严重疟疾贫血(SMA)是居住在恶性疟原虫全流行传播区的婴幼儿最常见的严重疟疾临床表现。SMA在全球疟疾可归因性发病率和死亡率中所占比例最大。SMA的病理生理机制是复杂的和多因素的，可归因于感染和未感染红细胞的直接和间接破坏、红细胞生成抑制、红细胞吞噬功能和细胞因子产生的失调。然而，缺乏关于SMA免疫学基础的信息是一个重大障碍，因为成功的疟疾疫苗必须预防威胁生命的SMA的发展。在许多炎症性疾病中，不同的B细胞亚群调节与疾病结局相关的保护性和致病性免疫反应。先前的研究表明，循环记忆B细胞和调节性B细胞的改变与类风湿关节炎(RA)的疾病结局有关。其他研究表明，CXCR4和CXCR5的表面表达减少，细胞内SDF-1和BCA-1的表达增加与慢性人类免疫缺陷病毒、系统性红斑狼疮和类风湿性关节炎相关。由于NA、记忆性和效应性B细胞亚群主要产生IL-10、肿瘤坏死因子和干扰素，这些亚群的差异表达可能是SMA儿童疾病严重程度的重要决定因素。对人类疟疾的研究表明，在反复感染后，B细胞通过逐渐积累特定的记忆B细胞和抗体滴度来调节疟疾免疫。由于细胞因子/趋化因子及其受体可以调节B细胞亚群和红细胞的生成，目前的建议将探讨不同的B细胞亚群(表达CXCR4/BCA-1和CXCR5/SDF-1)在调节SMA的发展和抑制红系发育中的作用。更多的研究表明，通过IgE/CD23途径激活的B细胞促进了红细胞生成抑制介质的产生，如MIP-1。此外，升高的免疫球蛋白E和可溶性(S)CD23与儿童疟疾严重程度的增加有关。此外，在小鼠模型中，IgE/CD23轴的激活增加与严重的贫血有关。由于CD23和MIP-1均调节IgE的合成，且与血红蛋白水平呈负相关，因此我们将探讨B细胞表达的IgE/CD23和MIP-1在SMA发生发展中的作用。这项建议还将确定恶性疟原虫来源的血吸虫蛋白(PfHZ)在TLR9(CD289)激活后对IgE类转换和细胞因子/趋化因子B细胞表达的影响。尽管PfHz可以促进抗体类别的转换和CD289的激活，但到目前为止还没有关于SMA儿童的研究。这项建议的总体目标是研究不同的B细胞亚群和IgE/CD23轴在调节居住在肯尼亚西部恶性疟原虫传播区3岁以下儿童SMA发展中的作用。这一建议的总体假设是，PfHz改变了细胞因子(IL-10、肿瘤坏死因子和干扰素)和趋化因子(SDF-1、BCA-1和MIP-1)的产生，进而促进B细胞亚群分化为不同的效应和调节表型。为了实现实验目标，我们将采用以医院为基础的前瞻性研究，纵向随访周期为36个月。由于对SMA产生保护性免疫所需的基本分子基础仍未明确，我们的研究将集中在细胞因子(IL-10、肿瘤坏死因子和干扰素)、趋化因子(即CXCR4/SDF-1、CXCR5/BCA-1和CCR5/MIP-1)和PfHZ调节B细胞亚群和SMA发生发展的能力。由于这项建议将在广泛表型的儿童队列中进行研究，我们将最大限度地提高我们成功识别那些影响SMA发展的B细胞亚群的能力。

DESCRIPTION (provided by applicant): Severe malarial anemia (SMA) is the most common clinical manifestation of severe malaria in infants and young children living in holoendemic Plasmodium falciparum transmission areas. SMA accounts for the greatest degree of global malaria-attributable morbidity and mortality. The pathophysiology of SMA is complex and multi-factorial and has been attributed to direct and indirect destruction of infected and uninfected erythrocytes, suppression of erythropoiesis, erythrophagocytosis, and dysregulation in cytokine production. However, the paucity of information on the immunological basis of SMA is a significant hindrance since a successful malaria vaccine must protect against development of life-threatening SMA. Different B cell subsets regulate protective and pathogenic immune responses associated with disease outcomes in a number of inflammatory mediated-diseases. Previous studies showed that alterations in the circulating memory B cells and regulatory B cells are associated with disease outcomes in rheumatoid arthritis (RA). Additional studies demonstrated that decreased surface expression of CXCR4 and CXCR5 and increased intracellular SDF-1α and BCA-1 expression are associated with chronic human immunodeficiency virus, systemic lupus erythromatosus, and RA. Since na¿ve, memory and effector B cell subsets predominantly produce IL-10, TNF-α, and IFN-γ, differential expression of these subsets may be important determinants of disease severity in children with SMA. Studies in human malaria indicate that B cells mediate malarial immunity through gradual accumulation of specific memory B cells and antibody titers following repeated infection. Since cytokines/chemokines, and their receptors, can modulate B cell subsets and erythropoiesis, the current proposal will explore the role of different B cell subsets (expressing CXCR4/BCA-1 and CXCR5/SDF-1α) in conditioning the development of SMA and suppression of erythroid development. Additional studies showed that increased activation of B cells through the IgE/CD23 pathway promotes increased production of erythropoietic suppressive mediators such as MIP-1α. In addition, elevated IgE and soluble (s)CD23 are associated with increased severity of pediatric malaria. Moreover, increased activation of the IgE/CD23 axis is associated with profound anemia in murine models. Since, both CD23 and MIP-1α regulate IgE synthesis, and are inversely correlated with hemoglobin levels, we will determine the effect of B cell expression of IgE/CD23 and MIP-1α on the development of SMA. This proposal will also determine the effect of Plasmodium falciparum-derived hemozoin (PfHz) on IgE class switching and cytokine/chemokine B cell expression following activation of TLR9 (CD289). Although PfHz can promote antibody class switching and activation of CD289, no studies to date have been performed in children with SMA. The overall objective of this proposal is to investigate the role of different B cell subsets and the IgE/CD23 axis in regulatin the development of SMA in children less than 3 years of age residing in a holoendemic P. falciparum transmission area of western Kenya. The overall hypothesis of this proposal is that PfHz alters the production of cytokines (IL-10, TNF-α, and IFN-γ) and chemokines (SDF-1α, BCA-1 and MIP-1α) which, in turn, promote differentiation of B cell subsets into different effector and regulatory phenotypes. To accomplish the experimental objectives, we will utilize a hospital-based prospective study with a longitudinal follow-up perio of 36 months. Since the underlying molecular basis required for development of protective immunity against SMA remains largely undefined, our investigations will focus on the ability of cytokines (IL-10, TNF-α, and IFN-γ), chemokines (i.e., CXCR4/SDF-1α, CXCR5/BCA-1 and CCR5/MIP-1α), and PfHz to modulate B cell subsets and development of SMA. Since this proposal will perform investigations in extensively phenotyped cohorts of children, we will maximize our ability to successfully identify those B cell subsets tha influence the development of SMA.