Anopheles gambiae Immune Responses to Human and Rodent <em>Plasmodium</em> Parasite Species

Transmission of malaria is dependent on the successful completion of the Plasmodium lifecycle in the Anopheles vector. Major obstacles are encountered in the midgut tissue, where most parasites are killed by the mosquito's immune system. In the present study, DNA microarray analyses have been used to compare Anopheles gambiae responses to invasion of the midgut epithelium by the ookinete stage of the human pathogen Plasmodium falciparum and the rodent experimental model pathogen P. berghei. Invasion by P. berghei had a more profound impact on the mosquito transcriptome, including a variety of functional gene classes, while P. falciparum elicited a broader immune response at the gene transcript level. Ingestion of human malaria-infected blood lacking invasive ookinetes also induced a variety of immune genes, including several anti-Plasmodium factors. Twelve selected genes were assessed for effect on infection with both parasite species and bacteria using RNAi gene silencing assays, and seven of these genes were found to influence mosquito resistance to both parasite species. An MD2-like receptor, AgMDL1, and an immunolectin, FBN39, showed specificity in regulating only resistance to P. falciparum, while the antimicrobial peptide gambicin and a novel putative short secreted peptide, IRSP5, were more specific for defense against the rodent parasite P. berghei. While all the genes that affected Plasmodium development also influenced mosquito resistance to bacterial infection, four of the antimicrobial genes had no effect on Plasmodium development. Our study shows that the impact of P. falciparum and P. berghei infection on A. gambiae biology at the gene transcript level is quite diverse, and the defense against the two Plasmodium species is mediated by antimicrobial factors with both universal and Plasmodium-species specific activities. Furthermore, our data indicate that the mosquito is capable of sensing infected blood constituents in the absence of invading ookinetes, thereby inducing anti-Plasmodium immune responses.疟疾的传播依赖于疟原虫（Plasmodium）在按蚊（Anopheles）媒介体内完成完整生命周期。蚊虫中肠组织是疟原虫传播的主要障碍，绝大多数疟原虫会在此被蚊虫的免疫系统杀灭。本研究采用DNA微阵列（DNA microarray）分析技术，比较了冈比亚按蚊（Anopheles gambiae）对两种疟原虫侵袭其中肠上皮细胞的响应：一种是引发人类疟疾的病原体恶性疟原虫（Plasmodium falciparum）的动合子（ookinete）阶段，另一种是啮齿类实验模型病原体伯氏疟原虫（Plasmodium berghei）。伯氏疟原虫的侵袭对蚊虫转录组的影响更为显著，涉及多种功能基因类别；而恶性疟原虫则在基因转录水平引发了更广泛的免疫应答。当蚊虫摄入不含侵袭性动合子的人类疟疾感染血液时，同样会诱导多种免疫基因的表达，包括多种抗疟原虫因子。研究人员选取12个候选基因，通过RNA干扰（RNAi）基因沉默实验评估其对两种疟原虫及细菌感染的影响，结果发现其中7个基因可调控蚊虫对两种疟原虫的抗性。一种MD2样受体AgMDL1以及一种免疫凝集素FBN39，仅在调控蚊虫对抗恶性疟原虫的抗性中表现出特异性；而抗菌肽冈比亚菌素（gambicin）以及一种新型潜在短分泌肽IRSP5，则更特异地参与抵御啮齿类病原体伯氏疟原虫。所有影响疟原虫发育的基因同时也会影响蚊虫对细菌感染的抗性，但其中4种抗菌基因对疟原虫的发育并无作用。本研究表明，恶性疟原虫与伯氏疟原虫感染在基因转录水平对冈比亚按蚊生物学的影响存在显著差异，宿主对两种疟原虫的防御由兼具广谱活性与疟原虫物种特异性的抗菌因子所介导。此外，本研究数据证实，蚊虫能够在无侵袭性动合子入侵的情况下感知感染血液中的相关成分，从而诱导抗疟原虫的免疫应答。