Reynolds, R. A. | bioRxiv Science

bioRxiv2019

20-hydroxyecdysone (20E) primes innate immune responses that limit bacteria and malaria parasite survival in Anopheles gambiae

Blood-feeding is an integral behavior of mosquitoes to acquire nutritional resources needed for reproduction. This requirement also enables mosquitoes to serve as efficient vectors to acquire and potentially transmit a multitude of mosquito-borne diseases, most notably malaria. Recent studies suggest that mosquito immunity is stimulated following a blood meal, independent of infection status. Since blood-feeding results in the increased production of the hormone 20-hydroxyecdysone (20E), we hypothesized that 20E may play an important role in priming the immune response for pathogen challenge. Herein, we examine the immunological effects of priming in Anopheles gambiae with 20E prior to pathogen infection, demonstrating a significant reduction in bacteria and Plasmodium berghei survival in the mosquito host. RNA-seq analysis following 20E treatment identifies several known 20E-regulated genes, as well as several immune genes with previously reported function in anti-pathogen defense. This includes the anti-microbial peptide cecropin 3, which we demonstrate its role as an antagonist of bacteria and Plasmodium in Anopheles gambiae and provide support that these responses are under temporal regulation. Together, these data demonstrate that 20E influences cellular immune function and anti-pathogen immunity following mosquito blood-feeding, arguing the importance of hormones in the regulation of mosquito innate immune function.

immunology↗

bioRxiv2019

Malaria parasite immune evasion and adaptation to its mosquito host is influenced by the acquisition of multiple blood meals

A minimum of two blood meals are required for a mosquito to acquire and transmit malaria, yet Anopheles mosquitoes frequently obtain additional blood meals during their adult lifespan. To determine the impact of subsequent blood-feeding on parasite development in Anopheles gambiae, we examined rodent and human Plasmodium parasite infection with or without an additional non-infected blood meal. We find that an additional blood meal significantly reduces P. berghei immature oocyst numbers, yet does not influence mature oocysts that have already begun sporogony. This is in contrast to experiments performed with the human parasite, P. falciparum, where an additional blood meal does not affect oocyst numbers. These observations are reproduced when mosquitoes were similarly challenged with an artificial protein meal, suggesting that parasite losses are due to the physical distension of the mosquito midgut. We provide evidence that feeding compromises the integrity of the midgut basal lamina, enabling the recognition and lysis of immature P. berghei oocysts by the mosquito complement system. Moreover, we demonstrate that additional feeding promotes P. falciparum oocyst growth, suggesting that human malaria parasites exploit host resources provided with blood-feeding to accelerate their growth. This contrasts experiments with P. berghei, where the size of surviving oocysts is independent of an additional blood meal. Together, these data demonstrate differences in the ability of Plasmodium species to evade immune detection and adapt to utilize host resources at the oocyst stage, representing an additional, yet unexplored component of vectorial capacity that has important implications for transmission of malaria.

microbiology↗