Maturation of human humoral immunity through repeat malaria challenges

疟疾仍然是世界上最致命的传染病之一， 每年有100万人。与许多病毒感染不同，儿童通常有反复的临床发作，但 成年后，大多数生活在流行地区的人都能免受疾病的侵害，而不是寄生虫 马车这种对寄生虫的逐渐反应的原因还没有很好地确定。最终抗体 在成年人中产生，当被动转移到患有疟疾的儿童时， 表明抗体介导的免疫的作用。然而，研究这种缓慢的发展一直很困难 由于没有办法控制寄生虫株或暴露， 时机动物研究虽然允许对特定的寄生虫菌株进行控制接种，但很复杂， 由于宿主和寄生虫物种之间的差异，适用于人类感染。为了解决这些限制， 我们进行了一项临床试验，系统地评估了疟疾初治志愿者对一种 最初接触未感染的蚊子，2个月后接触恶性疟原虫（Pf）感染的蚊子 蚊子叮咬，然后2 - 3次随后的挑战，每次用感染相同菌株的蚊子 一等兵使用受控人类疟疾感染（CHMI）模型可以控制寄生虫的时间 因此，可以直接监测暴露以及对连续感染的早期反应。观察到 在疟疾流行国家的儿童中，最初天真的志愿者继续受到感染， 多重感染挑战，但血液涂片阳性（称为通畅性）的时间增加 明显超时。第3次和第4次激发时症状显著减轻，表明开始 临床免疫力和初步数据表明通畅延迟时间最长的2例受试者的血浆 减少肝细胞侵袭与红细胞前免疫的发展一致。这个独特的，嗯- 控制感染模型使我们能够仔细地跟踪抗体分泌浆细胞的产生， 寄生虫特异性记忆B细胞，从寄生虫暴露前到用蚊子攻击3至4次 感染了同一种恶性疟原虫我们初步分析了循环免疫缺陷病毒的抗体库， 浆细胞表现出明显的克隆扩增，随后是群体崩溃和 不同的克隆我们推测，受寄生虫刺激的B细胞优先增殖和分化 转化为浆细胞而不是记忆细胞这样的模型可以解释为什么在大脑中缺乏持续的记忆反应， 感染和随后延迟获得免疫力。具体目标是：1）表征寄生虫- 特异性记忆B细胞产生。2)评估寄生虫特异性记忆B细胞 在每次CHMI后分离体外寄生虫刺激。3)评估Pf肝脏和血液阶段生长抑制 通过反复的CHMI。总之，这些结果将促进我们对记忆反应的理解， 疟原虫，这对保护性免疫的发展至关重要。

Malaria continues to be among the world’s most virulent infectious diseases accounting for the death of ~0.4 million people a year. Unlike many viral infections, children usually have repeated clinical episodes, but by adulthood, the majority of individuals living in endemic areas are protected against disease, not parasite carriage. The reasons for this gradual response to the parasite are not well established. Eventually antibodies are produced in adults that reduce parasitemia and fever when passively transferred to children with malaria, indicating a role for antibody-mediated immunity. However, it has been difficult to study this slow development of immunity to natural infection in the field, since there is no way to control for parasite strain or exposure timing. Animal studies, while allowing controlled inoculations of specific parasite strains, are complicated to apply to human infections due to differences across host and parasite species. To address these limitations, we carried out a clinical trial to systematically evaluate the immune response of malaria-naïve volunteers to an initial exposure to uninfected mosquitoes, followed 2 months later with Plasmodium falciparum (Pf)-infected mosquito bites and then 2-3 subsequent challenges each with the mosquitoes infected with the same strain of Pf. The use of the controlled human malaria infection (CHMI) model allowed control of the timing of parasite exposure and therefore the early response to sequential infections could be directly monitored. As observed with children in malaria endemic countries, the initially naïve volunteers continued to be susceptible through the multiple infectious challenges, but the time to a positive blood smear, termed patency, increased significantly overtime. Symptoms decreased significantly by the 3rd and 4th challenges indicating the beginning of clinical immunity and preliminary data indicates plasma from the two subjects with the longest patency delay reduced liver cell invasion consistent with the development of pre-erythrocytic immunity. This unique, well- controlled infection model allows us to carefully follow the production of antibody-secreting plasma cells and parasite-specific memory B cells from before parasite exposure through 3 to 4 challenges with mosquitoes infected with the same strain of P. falciparum. Our preliminary analysis of the antibody repertoire of circulating plasma cells demonstrates marked clonal expansion followed by population collapse and the appearance of distinct clones. We hypothesize that B cells stimulated by the parasite proliferate and differentiate preferentially into plasma cells, not memory cells. Such a model could explain the lack of a sustained memory response to infection and subsequent delay in the acquisition of immunity. The specific aims are 1) Characterize parasite- specific memory B cell production through repeat challenges. 2) Evaluate parasite-specific memory B cells isolated after each CHMI to parasite stimulation in vitro. 3) Assess the Pf liver and blood stage growth inhibition through repeated CHMI. Together the results will advance our understanding of the memory response to Plasmodium, which is critical for the development of protective immunity.