Late sporogonic stages of Plasmodium parasites are susceptible to the melanization response in Anopheles gambiae mosquitoes.

The malaria-causing parasites have to complete a complex infection cycle in the mosquito vector that also involves attack by the insect's innate immune system, especially at the early stages of midgut infection. However, Anopheles immunity to the late Plasmodium sporogonic stages, such as oocysts, has received little attention as they are considered to be concealed from immune factors due to their location under the midgut basal lamina and for harboring an elaborate cell wall comprising an external layer derived from the basal lamina that confers self-properties to an otherwise foreign structure. Here, we investigated whether Plasmodium berghei oocysts and sporozoites are susceptible to melanization-based immunity in Anopheles gambiae. Silencing of the negative regulator of melanization response, CLIPA14, increased melanization prevalence without significantly increasing the numbers of melanized oocysts, while co-silencing CLIPA14 with CLIPA2, a second negative regulator of melanization, resulted in a significant increase in melanized oocysts and melanization prevalence. Only late-stage oocysts were found to be melanized, suggesting that oocyst rupture was a prerequisite for melanization-based immune attack, presumably due to the loss of the immune-evasive features of their wall. We also found melanized sporozoites inside oocysts and in the hemocoel, suggesting that sporozoites at different maturation stages are susceptible to melanization. Silencing the melanization promoting factors TEP1 and CLIPA28 rescued oocyst melanization in CLIPA2/CLIPA14 co-silenced mosquitoes. Interestingly, silencing of CTL4, that protects early stage ookinetes from melanization, had no effect on oocysts and sporozoites, indicating differential regulation of immunity to early and late sporogonic stages. Similar to previous studies addressing ookinete stage melanization, the melanization of Plasmodium falciparum oocysts was significantly lower than that observed for P. berghei. In summary, our results provide conclusive evidence that late sporogonic malaria parasite stages are susceptible to melanization, and we reveal distinct regulatory mechanisms for ookinete and oocyst melanization.

Gene expression analysis of Anopheles Meigen, 1818 (Diptera: Culicidae) innate immunity after Plasmodium Marchiafava & Celli, 1885 (Apicomplexa) infection: Toward developing new malaria control strategies.

Despite the critical role of the Anopheles innate immune system in defending against Plasmodium infection, there is still limited information about the key immune mechanisms in Anopheles. This review assesses recent findings on the expression characteristics of immune-related genes in Anopheles following exposure to Plasmodium. A literature review, unrestricted by publication date, was conducted to evaluate immune-related gene expression in different organs of Anopheles after Plasmodium infection. Mosquito immune responses in the midgut are essential for reducing parasite populations. Additionally, innate immune responses in the salivary glands and hemocytes circulating in the hemocoel play key roles in defense against the parasite. Transcriptomic analysis of the mosquito's innate immune response to Plasmodium infection provides valuable insights into key immune mechanisms in mosquito defense. A deeper understanding of immune mechanisms in different organs of Anopheles following Plasmodium infection will aid in discovering critical targets for designing novel control strategies.

Malaria transmission blocking activity of Anopheles stephensi alanyl aminopeptidase N antigen formulated with MPL, CpG, and QS21 adjuvants.

BACKGROUNDS: Malaria, a preventive and treatable disease, is still responsible for annual deaths reported in most tropical regions, principally in sub-Saharan Africa. Subunit recombinant transmission-blocking vaccines (TBVs) have been proposed as promising vaccines to succeed in malaria elimination and eradication. Here, a provisional study was designed to assess the immunogenicity and functional activity of alanyl aminopeptidase N (APN1) of Anopheles stephensi, as a TBV candidate, administered with MPL, CpG, and QS21 adjuvants in the murine model. METHODOLOGY/PRINCIPAL FINDINGS: The mouse groups were immunized with recombinant APN1 (rAPN1) alone or formulated with CpG, MPL, QS-21, or a combination of adjuvants (CMQ), and the elicited immune responses were evaluated after the third immunization. The standard membrane feeding assay (SMFA) measured the functional activity of antibodies against bacterial-expressed APN1 protein in adjuvanted vaccine groups on transmission of P. falciparum (NF54) to An. stephensi mosquitoes. Evaluation of mice vaccinated with rAPN1 formulated with distinct adjuvants manifested a significant increase in the high-avidity level of anti-APN1 IgG and IgG subclasses; however, rAPN1 induced the highest level of high-avidity anti-APN1 IgG1, IgG2a, and IgG2b antibodies in the immunized vaccine group 5 (APN1/CMQ). In addition, vaccine group 5 (receiving APN1/CMQ), had still the highest level of anti-APN1 IgG antibodies relative to other immunized groups after six months, on day 180. The SMFA data indicates a trend towards higher transmission-reducing activity in groups 2 and 5, which received the antigen formulated with CpG or a combination of three adjuvants. CONCLUSIONS/SIGNIFICANCE: The results have shown the capability of admixture to stimulate high-affinity and long-lasting antibodies against the target antigen to hinder Plasmodium parasite development in the mid-gut of An. stephensi. The attained results authenticated APN1/CMQ and APN1/CpG as a potent APN1-based TBV formulation which will be helpful in designing a vaccine in the future.

Utility of plasma anti-gSG6-P1 IgG levels in determining changes in Anopheles gambiae bite rates in a rural area of Cameroon.

The applicability of the specific human IgG antibody response to Anopheles gambiae salivary Gland Protein-6 peptide 1 (gSG6-P1 salivary peptide) as a biomarker able to distinguish the level of exposure to mosquito bites according to seasonal variations has not yet been evaluated in Central African regions. The study aimed to provide the first reliable data on the IgG anti-gSG6-P1 response in rural area in Cameroon according to the dry- and rainy-season. Between May and December 2020, dry blood samples were collected from people living in the Bankeng village in the forest area of the Centre region of Cameroon. Malaria infection was determined by thick-blood smear microscopy and multiplex PCR. The level of IgG anti-gSG6-P1 response, was assessed by enzyme-linked immunosorbent assay. Anopheles density and aggressiveness were assessed using human landing catches. The prevalence of malaria infection remains significantly higher in the rainy season than in the dry season (77.57% vs 61.44%; p = 0.0001). The specific anti-gSG6-P1 IgG response could be detected in individuals exposed to few mosquito bites and showed inter-individual heterogeneity even when living in the same exposure area. In both seasons, the level of anti-gSG6-P1 IgG response was not significantly different between Plasmodium infected and non-infected individuals. Mosquito bites were more aggressive in the rainy season compared to the dry season (human biting rate-HBR of 15.05 b/p/n vs 1.5 b/p/n) where mosquito density was very low. Infected mosquitoes were found only during the rainy season (sporozoite rate = 10.63% and entomological inoculation rate-EIR = 1.42 ib/p/n). The level of IgG anti-gSG6-P1 response was significantly higher in the rainy season and correlated with HBR (p ˂ 0.0001). This study highlights the high heterogeneity of individual's exposure to the Anopheles gambiae s.l vector bites depending on the transmission season in the same area. These findings reinforce the usefulness of the anti-gSG6-P1 IgG response as an accurate immunological biomarker for detecting individual exposure to Anopheles gambiae s.l. bites during the low risk period of malaria transmission in rural areas and for the differentiating the level of exposure to mosquitoes.

Extracellular matrix proteins Pericardin and Lonely heart mediate periostial hemocyte aggregation in the mosquito Anopheles gambiae.

An infection induces the migration of immune cells called hemocytes to the insect heart, where they aggregate around heart valves called ostia and phagocytose pathogens in areas of high hemolymph flow. Here, we investigated whether the cardiac extracellular matrix proteins, Pericardin (Prc) and Lonely heart (Loh), regulate the infection-induced aggregation of periostial hemocytes in the mosquito, An. gambiae. We discovered that RNAi-based post-transcriptional silencing of Prc or Loh did not affect the resident population of periostial hemocytes in uninfected mosquitoes, but that knocking down these genes decreases the infection-induced migration of hemocytes to the heart. Knocking down Prc or Loh did not affect the proportional distribution of periostial hemocytes along the periostial regions. Moreover, knocking down Prc or Loh did not affect the number of sessile hemocytes outside the periostial regions, suggesting that the role of these proteins is cardiac-specific. Finally, knocking down Prc or Loh did not affect the amount of melanin at the periostial regions, or the intensity of an infection at 24 h after challenge. Overall, we demonstrate that Prc and Loh are positive regulators of the infection-induced migration of hemocytes to the heart of mosquitoes.

Basophil-Derived IL-4 and IL-13 Protect Intestinal Barrier Integrity and Control Bacterial Translocation during Malaria.

Our previous work demonstrated that basophils regulate a suite of malaria phenotypes, including intestinal mastocytosis and permeability, the immune response to infection, gametocytemia, and parasite transmission to the malaria mosquito Anopheles stephensi. Given that activated basophils are primary sources of the regulatory cytokines IL-4 and IL-13, we sought to examine the contributions of these mediators to basophil-dependent phenotypes in malaria. We generated mice with basophils depleted for IL-4 and IL-13 (baso IL-4/IL-13 (-)) and genotype controls (baso IL-4/IL-13 (+)) by crossing mcpt8-Cre and Il4/Il13fl/fl mice and infected them with Plasmodium yoelii yoelii 17XNL. Conditional deletion was associated with ileal mastocytosis and mast cell (MC) activation, increased intestinal permeability, and increased bacterial 16S levels in blood, but it had no effect on neutrophil activation, parasitemia, or transmission to A. stephensi. Increased intestinal permeability in baso IL-4/IL-13 (-) mice was correlated with elevated plasma eotaxin (CCL11), a potent eosinophil chemoattractant, and increased ileal MCs, proinflammatory IL-17A, and the chemokines MIP-1α (CCL3) and MIP-1ß (CCL4). Blood bacterial 16S copies were positively but weakly correlated with plasma proinflammatory cytokines IFN-γ and IL-12p40, suggesting that baso IL-4/IL-13 (-) mice failed to control bacterial translocation into the blood during malaria infection. These observations suggest that basophil-derived IL-4 and IL-13 do not contribute to basophil-dependent regulation of parasite transmission, but these cytokines do orchestrate protection of intestinal barrier integrity after P. yoelii infection. Specifically, basophil-dependent IL-4/IL-13 control MC activation and prevent infection-induced intestinal barrier damage and bacteremia, perhaps via regulation of eosinophils, macrophages, and Th17-mediated inflammation.

Wolbachia infection-responsive immune genes suppress Plasmodium falciparum infection in Anopheles stephensi.

Wolbachia, a maternally transmitted symbiotic bacterium of insects, can suppress a variety of human pathogens in mosquitoes, including malaria-causing Plasmodium in the Anopheles vector. However, the mechanistic basis of Wolbachia-mediated Plasmodium suppression in mosquitoes is not well understood. In this study, we compared the midgut and carcass transcriptomes of stably infected Anopheles stephensi with Wolbachia wAlbB to uninfected mosquitoes in order to discover Wolbachia infection-responsive immune genes that may play a role in Wolbachia-mediated anti-Plasmodium activity. We show that wAlbB infection upregulates 10 putative immune genes and downregulates 14 in midguts, while it upregulates 31 putative immune genes and downregulates 15 in carcasses at 24 h after blood-fed feeding, the time at which the Plasmodium ookinetes are traversing the midgut tissue. Only a few of these regulated immune genes were also significantly differentially expressed between Wolbachia-infected and non-infected midguts and carcasses of sugar-fed mosquitoes. Silencing of the Wolbachia infection-responsive immune genes TEP 4, TEP 15, lysozyme C2, CLIPB2, CLIPB4, PGRP-LD and two novel genes (a peritrophin-44-like gene and a macro domain-encoding gene) resulted in a significantly greater permissiveness to P. falciparum infection. These results indicate that Wolbachia infection modulates mosquito immunity and other processes that are likely to decrease Anopheles permissiveness to Plasmodium infection.

An Aedes-Anopheles Vaccine Candidate Supplemented with BCG Epitopes Against the Aedes and Anopheles Genera to Overcome Hypersensitivity to Mosquito Bites.

BACKGROUND: Skeeter syndrome is a severe local allergic response to mosquito bites that is accompanied by considerable inflammation and, in some cases, a systemic response like fever. People with the syndrome develop serious allergies, ranging from rashes to anaphylaxis or shock. The few available studies on mosquito venom immunotherapy have utilized whole-body preparations and small sample sizes. Still, owing to their little success, vaccination remains a promising alternative as well as a permanent solution for infections like Skeeter's. METHODS: This study, therefore, illustrated the construction of an epitope-based vaccine candidate against Skeeter Syndrome using established immunoinformatic techniques. We selected three species of mosquitoes, Anopheles melas, Anopheles funestus, and Aedes aegypti, to derive salivary antigens usually found in mosquito bites. Our construct was also supplemented with bacterial epitopes known to elicit a strong TH1 response and suppress TH2 stimulation that is predicted to reduce hypersensitivity against the bites. RESULTS: A quality factor of 98.9496, instability index of 38.55, aliphatic index of 79.42, solubility of 0.934747, and GRAVY score of -0.02 indicated the structural (tertiary and secondary) stability, thermostability, solubility, and hydrophilicity of the construct, respectively. The designed Aedes-Anopheles vaccine (AAV) candidate was predicted to be flexible and less prone to deformability with an eigenvalue of 1.5911e-9 and perfected the human immune response against Skeeter (hypersensitivity) and many mosquito-associated diseases as we noted the production of 30,000 Th1 cells per mm3 with little (insignificant production of Th2 cells. The designed vaccine also revealed stable interactions with the pattern recognition receptors of the host. The TLR2/vaccine complex interacted with a free energy of - 1069.2 kcal/mol with 26 interactions, whereas the NLRP3/vaccine complex interacted with a free energy of - 1081.2 kcal/mol with 16 molecular interactions. CONCLUSION: Although being a pure in-silico study, the in-depth analysis performed herein speaks volumes of the potency of the designed vaccine candidate predicting that the proposition can withstand rigorous in-vitro and in-vivo clinical trials and may proceed to become the first preventative immunotherapy against mosquito bite allergy.

C-type lectin 4 regulates broad-spectrum melanization-based refractoriness to malaria parasites.

Anopheles gambiae melanization-based refractoriness to the human malaria parasite Plasmodium falciparum has rarely been observed in either laboratory or natural conditions, in contrast to the rodent model malaria parasite Plasmodium berghei that can become completely melanized by a TEP1 complement-like system-dependent mechanism. Multiple studies have shown that the rodent parasite evades this defense by recruiting the C-type lectins CTL4 and CTLMA2, while permissiveness to the human malaria parasite was not affected by partial depletion of these factors by RNAi silencing. Using CRISPR/Cas9-based CTL4 knockout, we show that A. gambiae can mount melanization-based refractoriness to the human malaria parasite, which is independent of the TEP1 complement-like system and the major anti-Plasmodium immune pathway Imd. Our study indicates a hierarchical specificity in the control of Plasmodium melanization and proves CTL4 as an essential host factor for P. falciparum transmission and one of the most potent mosquito-encoded malaria transmission-blocking targets.

A Mosquito AgTRIO Monoclonal Antibody Reduces Early Plasmodium Infection of Mice.

Malaria begins when an infected mosquito injects saliva containing Plasmodium sporozoites into the skin of a vertebrate host. Passive immunization of mice with antiserum against the Anopheles gambiae mosquito saliva protein TRIO (AgTRIO) offers significant protection against Plasmodium infection of mice. Furthermore, passive transfer of both AgTRIO antiserum and an anti-circumsporozoite protein monoclonal antibody provides synergistic protection. In this study, we generated monoclonal antibodies against AgTRIO to delineate the regions of AgTRIO associated with protective immunity. Monoclonal antibody 13F-1 markedly reduced Plasmodium infection in mice and recognized a region (VDDLMAKFN) in the carboxyl terminus of AgTRIO. 13F-1 is an IgG2a isotype monoclonal antibody, and the Fc region is required for protection. These data will aid in the generation of future malaria vaccines that may include both pathogen and vector antigens.

Immunomodulation by Mosquito Salivary Protein AgSAP Contributes to Early Host Infection by Plasmodium.

Malaria is caused when Plasmodium sporozoites are injected along with saliva by an anopheline mosquito into the dermis of a vertebrate host. Arthropod saliva has pleiotropic effects that can influence local host responses, pathogen transmission, and exacerbation of the disease. A mass spectrometry screen identified mosquito salivary proteins that are associated with Plasmodium sporozoites during saliva secretions. In this study, we demonstrate that one of these salivary antigens, Anopheles gambiae sporozoite-associated protein (AgSAP), interacts directly with Plasmodium falciparum and Plasmodium berghei sporozoites. AgSAP binds to heparan sulfate and inhibits local inflammatory responses in the skin. The silencing of AgSAP in mosquitoes reduces their ability to effectively transmit sporozoites to mice. Moreover, immunization with AgSAP decreases the Plasmodium burden in mice that are bitten by Plasmodium-infected mosquitoes. These data suggest that AgSAP facilitates early Plasmodium infection in the vertebrate host and serves as a target for the prevention of malaria. IMPORTANCE Malaria is a vector-borne disease caused by Plasmodium sporozoites. When an anopheline mosquito bites its host, it releases Plasmodium sporozoites as well as saliva components. Mosquito proteins have the potential to serve as antigens to prevent or influence malaria without directly targeting the pathogen. This may help set a new paradigm for vaccine development. In this study, we have elucidated the role of a novel salivary antigen, named Anopheles gambiae sporozoite-associated protein (AgSAP). The results presented here show that AgSAP interacts with Plasmodium falciparum and Plasmodium berghei sporozoites and modulates local inflammatory responses in the skin. Furthermore, our results show that AgSAP is a novel mosquito salivary antigen that influences the early stages of Plasmodium infection in the vertebrate host. Individuals living in countries where malaria is endemic generate antibodies against AgSAP, which indicates that AgSAP can serve as a biomarker for disease prevalence and epidemiological analysis.

Anopheles salivary antigens as serological biomarkers of vector exposure and malaria transmission: A systematic review with multilevel modelling.

Background: Entomological surveillance for malaria is inherently resource-intensive and produces crude population-level measures of vector exposure which are insensitive in low-transmission settings. Antibodies against Anopheles salivary proteins measured at the individual level may serve as proxy biomarkers for vector exposure and malaria transmission, but their relationship is yet to be quantified. Methods: A systematic review of studies measuring antibodies against Anopheles salivary antigens (PROSPERO: CRD42020185449). Multilevel modelling (to account for multiple study-specific observations [level 1], nested within study [level 2], and study nested within country [level 3]) estimated associations between seroprevalence with Anopheles human biting rate (HBR) and malaria transmission measures. Results: From 3981 studies identified in literature searches, 42 studies across 16 countries were included contributing 393 study-specific observations of anti-Anopheles salivary antibodies determined in 42,764 samples. A positive association between HBR (log transformed) and seroprevalence was found; overall a twofold (100% relative) increase in HBR was associated with a 23% increase in odds of seropositivity (OR: 1.23, 95% CI: 1.10-1.37; p<0.001). The association between HBR and Anopheles salivary antibodies was strongest with concordant, rather than discordant, Anopheles species. Seroprevalence was also significantly positively associated with established epidemiological measures of malaria transmission: entomological inoculation rate, Plasmodium spp. prevalence, and malarial endemicity class. Conclusions: Anopheles salivary antibody biomarkers can serve as a proxy measure for HBR and malaria transmission, and could monitor malaria receptivity of a population to sustain malaria transmission. Validation of Anopheles species-specific biomarkers is important given the global heterogeneity in the distribution of Anopheles species. Salivary biomarkers have the potential to transform surveillance by replacing impractical, inaccurate entomological investigations, especially in areas progressing towards malaria elimination. Funding: Australian National Health and Medical Research Council, Wellcome Trust.

Recent Advances in Understanding the Inflammatory Response in Malaria: A Review of the Dual Role of Cytokines.

Malaria is a serious and, in some unfortunate cases, fatal disease caused by a parasite of the Plasmodium genus. It predominantly occurs in tropical areas where it is transmitted through the bite of an infected Anopheles mosquito. The pathogenesis of malaria is complex and incompletely elucidated. During blood-stage infection, in response to the presence of the parasite, the host's immune system produces proinflammatory cytokines including IL-6, IL-8, IFN-γ, and TNF, cytokines which play a pivotal role in controlling the growth of the parasite and its elimination. Regulatory cytokines such as transforming growth factor- (TGF-) ß and IL-10 maintain the balance between the proinflammatory and anti-inflammatory responses. However, in many cases, cytokines have a double role. On the one hand, they contribute to parasitic clearance, and on the other, they are responsible for pathological changes encountered in malaria. Cytokine-modulating strategies may represent a promising modern approach in disease management. In this review, we discuss the host immune response in malaria, analyzing the latest studies on the roles of pro- and anti-inflammatory cytokines.

Use of anti-gSG6-P1 IgG as a serological biomarker to assess temporal exposure to Anopheles' mosquito bites in Lower Moshi.

BACKGROUND: Malaria prevalence in the highlands of Northern Tanzania is currently below 1% making this an elimination prone setting. As climate changes may facilitate increasing distribution of Anopheles mosquitoes in such settings, there is a need to monitor changes in risks of exposure to ensure that established control tools meet the required needs. This study explored the use of human antibodies against gambiae salivary gland protein 6 peptide 1 (gSG6-P1) as a biomarker of Anopheles exposure and assessed temporal exposure to mosquito bites in populations living in Lower Moshi, Northern Tanzania. METHODS: Three cross-sectional surveys were conducted in 2019: during the dry season in March, at the end of the rainy season in June and during the dry season in September. Blood samples were collected from enrolled participants and analysed for the presence of anti-gSG6-P1 IgG. Mosquitoes were sampled from 10% of the participants' households, quantified and identified to species level. Possible associations between gSG6-P1 seroprevalence and participants' characteristics were determined. RESULTS: The total number of Anopheles mosquitoes collected was highest during the rainy season (n = 1364) when compared to the two dry seasons (n = 360 and n = 1075, respectively). The gSG6-P1 seroprevalence increased from 18.8% during the dry season to 25.0% during the rainy season (χ2 = 2.66; p = 0.103) followed by a significant decline to 11.0% during the next dry season (χ2 = 12.56; p = 0.001). The largest number of mosquitoes were collected in one village (Oria), but the seroprevalence was significantly lower among the residents as compared to the rest of the villages (p = 0.039), explained by Oria having the highest number of participants owning and using bed nets. Both individual and household gSG6-P1 IgG levels had no correlation with numbers of Anopheles mosquitoes collected. CONCLUSION: Anti-gSG6-P1 IgG is a potential tool in detecting and distinguishing temporal and spatial variations in exposure to Anopheles mosquito bites in settings of extremely low malaria transmission where entomological tools may be obsolete. However studies with larger sample size and extensive mosquito sampling are warranted to further explore the association between this serological marker and abundance of Anopheles mosquito.

Double peroxidase and histone acetyltransferase AgTip60 maintain innate immune memory in primed mosquitoes.

Immune priming in Anopheles gambiae is mediated by the systemic release of a hemocyte differentiation factor (HDF), a complex of lipoxin A4 bound to Evokin, a lipid carrier. HDF increases the proportion of circulating granulocytes and enhances mosquito cellular immunity. Here, we show that Evokin is present in hemocytes and fat-body cells, and messenger RNA (mRNA) expression increases significantly after immune priming. The double peroxidase (DBLOX) enzyme, present in insects but not in vertebrates, is essential for HDF synthesis. DBLOX is highly expressed in oenocytes in the fat-body tissue, and these cells increase in number in primed mosquitoes. We provide direct evidence that the histone acetyltransferase AgTip60 (AGAP001539) is also essential for a sustained increase in oenocyte numbers, HDF synthesis, and immune priming. We propose that oenocytes may function as a population of cells that are reprogrammed, and orchestrate and maintain a broad, systemic, and long-lasting state of enhanced immune surveillance in primed mosquitoes.

Immunopotentiation by Lymph-Node Targeting of a Malaria Transmission-Blocking Nanovaccine.

A successful malaria transmission blocking vaccine (TBV) requires the induction of a high antibody titer that leads to abrogation of parasite traversal of the mosquito midgut following ingestion of an infectious bloodmeal, thereby blocking the cascade of secondary human infections. Previously, we developed an optimized construct UF6b that elicits an antigen-specific antibody response to a neutralizing epitope of Anopheline alanyl aminopeptidase N (AnAPN1), an evolutionarily conserved pan-malaria mosquito midgut-based TBV target, as well as established a size-controlled lymph node targeting biodegradable nanoparticle delivery system that leads to efficient and durable antigen-specific antibody responses using the model antigen ovalbumin. Herein, we demonstrate that co-delivery of UF6b with the adjuvant CpG oligodeoxynucleotide immunostimulatory sequence (ODN ISS) 1018 using this biodegradable nanoparticle vaccine delivery system generates an AnAPN1-specific immune response that blocks parasite transmission in a standard membrane feeding assay. Importantly, this platform allows for antigen dose-sparing, wherein lower antigen payloads elicit higher-quality antibodies, therefore less antigen-specific IgG is needed for potent transmission-reducing activity. By targeting lymph nodes directly, the resulting immunopotentiation of AnAPN1 suggests that the de facto assumption that high antibody titers are needed for a TBV to be successful needs to be re-examined. This nanovaccine formulation is stable at -20°C storage for at least 3 months, an important consideration for vaccine transport and distribution in regions with poor healthcare infrastructure. Together, these data support further development of this nanovaccine platform for malaria TBVs.

Prostaglandin E2 Signaling Mediates Oenocytoid Immune Cell Function and Lysis, Limiting Bacteria and Plasmodium Oocyst Survival in Anopheles gambiae.

Lipid-derived signaling molecules known as eicosanoids have integral roles in mediating immune and inflammatory processes across metazoans. This includes the function of prostaglandins and their cognate G protein-coupled receptors (GPCRs) to employ their immunological actions. In insects, prostaglandins have been implicated in the regulation of both cellular and humoral immune responses, yet in arthropods of medical importance, studies have been limited. Here, we describe a prostaglandin E2 receptor (AgPGE2R) in the mosquito Anopheles gambiae and demonstrate that its expression is most abundant in oenocytoid immune cell populations. Through the administration of prostaglandin E2 (PGE2) and AgPGE2R-silencing, we demonstrate that prostaglandin E2 signaling regulates a subset of prophenoloxidases (PPOs) and antimicrobial peptides (AMPs) that are strongly expressed in populations of oenocytoids. We demonstrate that PGE2 signaling via the AgPGE2R significantly limits both bacterial replication and Plasmodium oocyst survival. Additional experiments establish that PGE2 treatment increases phenoloxidase (PO) activity through the increased expression of PPO1 and PPO3, genes essential to anti-Plasmodium immune responses that promote oocyst killing. We also provide evidence that the mechanisms of PGE2 signaling are concentration-dependent, where high concentrations of PGE2 promote oenocytoid lysis, negating the protective effects of lower concentrations of PGE2 on anti-Plasmodium immunity. Taken together, our results provide new insights into the role of PGE2 signaling on immune cell function and its contributions to mosquito innate immunity that promote pathogen killing.

Heat Shock Causes Lower Plasmodium Infection Rates in Anopheles albimanus.

The immune response of Anopheles mosquitoes to Plasmodium invasion has been extensively studied and shown to be mediated mainly by the nitric oxide synthase (NOS), dual oxidase (DUOX), phenoloxidase (PO), and antimicrobial peptides activity. Here, we studied the correlation between a heat shock insult, transcription of immune response genes, and subsequent susceptibility to Plasmodium berghei infection in Anopheles albimanus. We found that transcript levels of many immune genes were drastically affected by the thermal stress, either positively or negatively. Furthermore, the transcription of genes associated with modifications of nucleic acid methylation was affected, suggesting an increment in both DNA and RNA methylation. The heat shock increased PO and NOS activity in the hemolymph, as well as the transcription of several immune genes. As consequence, we observed that heat shock increased the resistance of mosquitoes to Plasmodium invasion. The data provided here could help the understanding of infection transmission under the ever more common heat waves.

Single-cell analysis of mosquito hemocytes identifies signatures of immune cell subtypes and cell differentiation.

Mosquito immune cells, known as hemocytes, are integral to cellular and humoral responses that limit pathogen survival and mediate immune priming. However, without reliable cell markers and genetic tools, studies of mosquito immune cells have been limited to morphological observations, leaving several aspects of their biology uncharacterized. Here, we use single-cell RNA sequencing (scRNA-seq) to characterize mosquito immune cells, demonstrating an increased complexity to previously defined prohemocyte, oenocytoid, and granulocyte subtypes. Through functional assays relying on phagocytosis, phagocyte depletion, and RNA-FISH experiments, we define markers to accurately distinguish immune cell subtypes and provide evidence for immune cell maturation and differentiation. In addition, gene-silencing experiments demonstrate the importance of lozenge in defining the mosquito oenocytoid cell fate. Together, our scRNA-seq analysis provides an important foundation for future studies of mosquito immune cell biology and a valuable resource for comparative invertebrate immunology.

A natural symbiotic bacterium drives mosquito refractoriness to Plasmodium infection via secretion of an antimalarial lipase.

The stalling global progress in the fight against malaria prompts the urgent need to develop new intervention strategies. Whilst engineered symbiotic bacteria have been shown to confer mosquito resistance to parasite infection, a major challenge for field implementation is to address regulatory concerns. Here, we report the identification of a Plasmodium-blocking symbiotic bacterium, Serratia ureilytica Su_YN1, isolated from the midgut of wild Anopheles sinensis in China that inhibits malaria parasites via secretion of an antimalarial lipase. Analysis of Plasmodium vivax epidemic data indicates that local malaria cases in Tengchong (Yunnan province, China) are significantly lower than imported cases and importantly, that the local vector A. sinensis is more resistant to infection by P. vivax than A. sinensis from other regions. Analysis of the gut symbiotic bacteria of mosquitoes from Yunnan province led to the identification of S. ureilytica Su_YN1. This bacterium renders mosquitoes resistant to infection by the human parasite Plasmodium falciparum or the rodent parasite Plasmodium berghei via secretion of a lipase that selectively kills parasites at various stages. Importantly, Su_YN1 rapidly disseminates through mosquito populations by vertical and horizontal transmission, providing a potential tool for blocking malaria transmission in the field.