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，造成约0.4人死亡 一年有一百万人。与许多病毒感染不同的是，儿童通常有反复的临床发作，但到了 成年后，大多数生活在流行地区的人受到保护，不会感染疾病，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得到很好的证实。最终抗体 在成人身上产生，当被动地转移到患有疟疾的儿童身上时，可以减少寄生虫血症和发烧， 这表明了抗体介导免疫的作用。然而，很难研究这种缓慢的发展。 对野外自然感染的免疫力，因为没有办法控制寄生虫的品系或暴露 时机到了。动物研究，虽然允许对特定的寄生虫菌株进行控制接种，但对于 适用于因宿主和寄生虫种类不同而引起的人类感染。为了解决这些限制， 我们进行了一项临床试验，系统地评估了幼稚疟疾志愿者对 最初接触未受感染的蚊子，2个月后感染恶性疟原虫(PF) 蚊子叮咬，然后2-3次随后的挑战，每次蚊子感染相同的菌株 Pf.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，可以直接监测对连续感染的早期反应。正如所观察到的 对于疟疾流行国家的儿童，最初天真的志愿者仍然容易受到 多重感染挑战，但血液涂片阳性的时间增加了，称为通畅性 大大加班了。第三次和第四次挑战时症状明显减少，表明开始 临床免疫力和初步数据表明两个受试者的血浆通畅时间最长 肝细胞侵袭减少与红细胞前免疫功能的发展相一致。这个独一无二的，好的- 控制感染模型使我们能够仔细跟踪抗体分泌浆细胞的产生和 寄生虫暴露前的寄生虫特异性记忆B细胞通过3到4次与蚊子的挑战 感染相同品系的恶性疟原虫。我们对循环抗体谱系的初步分析 浆细胞表现出明显的克隆性扩张，随后群体崩溃，并出现 截然不同的克隆人。我们假设寄生虫刺激的B细胞优先增殖和分化 变成浆细胞，而不是记忆细胞。这样的模型可以解释为什么缺乏持续的记忆反应 感染和随后获得免疫力的延迟。具体目标是1)描述寄生虫的特征- 通过重复挑战产生特定的记忆B细胞。2)评估寄生虫特异性记忆B细胞 每次分离后进行体外对寄生虫的刺激。3)评估PF对肝脏和血液期的生长抑制 通过重复的CHMI。总而言之，这些结果将促进我们对记忆反应的理解 疟原虫，这是发展保护性免疫的关键。

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.