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The facets of host control during Plasmodiumliver infection remain largely unknown. We find that the SLC7a11-GPX4 pathway, which has been associated with the production of reactive oxygen species, lipid peroxidation, and a form of cell death called ferroptosis, plays a critical role in control of Plasmodiumliver stage infection. Specifically, blocking GPX4 or SLC7a11 dramatically reduces Plasmodiumliver stage parasite infection. In contrast, blocking negative regulators of this pathway, NOX1 and TFR1, leads to an increase in liver stage infection. We have shown previously that increased levels of P53 reduces PlasmodiumLS burden in an apoptosis-independent manner. Here, we demonstrate that increased P53 is unable to control parasite burden during NOX1 or TFR1 knockdown, or in the presence of ROS scavenging or when lipid peroxidation is blocked. Additionally, SLC7a11 inhibitors Erastin and Sorafenib reduce infection. Thus, blocking the host SLC7a11-GPX4 pathway serves to selectively elevate lipid peroxides in infected cells, which localize within the parasite and lead to the elimination of liver stage parasites.

Background: Serious infections in persons who use drugs (PWUD) are rising. Dalbavancin, due to its extended half-life, offers an alternative treatment for patients in whom standard of care antibiotics are not feasible or practical, allowing for reduced hospital days and the avoidance of central line placement or the use of complex oral regimens.Objectives: We aim to describe the time and effort required for coordination of dalbavancin courses by outpatient registered nurses (RNs) and other outpatient parenteral antimicrobial therapy (OPAT) staff.Design and methods: We conducted a retrospective review of adult patients with documented substance use who received at least one dose of dalbavancin and quantified the number of interventions required by our OPAT RNs and other OPAT staff for coordination of dalbavancin courses. Additionally, detailed data on time spent per intervention were prospectively collected for a 1-month period.Results: A total of 52 patients with 53 dalbavancin courses were included. Most substance use was intravenous. Infectious diagnoses included bone and joint infections (61%) and endocarditis (7%), in addition to skin and soft tissue infections (19%). Infections were most commonly caused by Staphylococcus aureus(62%). RN intervention was required in the coordination of 60% of all courses and in 77% of courses in which at least one outpatient dose was needed. Adverse reactions occurred in one patient (2%) and 90-day readmissions due to infectious complications occurred in two patients (4%). Detailed time analysis was performed for seven consecutive patients, with a total of 179 min spent by OPAT RNs on coordination.Conclusions: The ease of dalbavancin administration does not eliminate the need for extensive RN coordination for successful administration of doses in the outpatient setting for PWUD. This need should be accounted for in program staffing to help increase successful dalbavancin course completion.

ABSTRACTAfter transmission by Anophelesmosquitoes, Plasmodiumsporozoites travel to the liver, infect hepatocytes, and rapidly develop as intrahepatocytic liver stages (LS). Rodent models of malaria exhibit large differences in the magnitude of liver infection, both between parasite species and between strains of mice. This has been mainly attributed to differences in innate immune responses and parasite infectivity. Here, we report that BALB/cByJ mice are more susceptible to Plasmodium yoeliipreerythrocytic infection than BALB/cJ mice. This difference occurs at the level of early hepatocyte infection, but expression levels of reported host factors that are involved in infection do not correlate with susceptibility. Interestingly, BALB/cByJ hepatocytes are more frequently polyploid; thus, their susceptibility converges on the previously observed preference of sporozoites to infect polyploid hepatocytes. Gene expression analysis demonstrates hepatocyte-specific differences in mRNA abundance for numerous genes between BALB/cByJ and BALB/cJ mice, some of which encode hepatocyte surface molecules. These data suggest that a yet-unknown receptor for sporozoite infection, present at elevated levels on BALB/cByJ hepatocytes and also polyploid hepatocytes, might facilitate Plasmodiumliver infection.

ABSTRACTPlasmodiumsporozoites develop within oocysts in the mosquito midgut wall and then migrate to the salivary glands. After transmission, they embark on a complex journey to the mammalian liver, where they infect hepatocytes. Proteins on the sporozoite surface likely mediate multiple steps of this journey, yet only a few sporozoite surface proteins have been described. Here, we characterize a novel, conserved sporozoite surface protein (SSP3) in the rodent malaria parasite Plasmodium yoelii. SSP3 is a putative type I transmembrane protein unique to Plasmodium. By using epitope tagging and SSP3-specific antibodies in conjunction with immunofluorescence microscopy, we showed that SSP3 is expressed in mosquito midgut oocyst sporozoites, exhibiting an intracellular localization. In sporozoites derived from the mosquito salivary glands, however, SSP3 localized predominantly to the sporozoite surface as determined by immunoelectron microscopy. However, the ectodomain of SSP3 appeared to be inaccessible to antibodies in nonpermeabilized salivary gland sporozoites. Antibody-induced shedding of the major surface protein circumsporozoite protein (CSP) exposed the SSP3 ectodomain to antibodies in some sporozoites. Targeted deletion of SSP3adversely affected in vitrosporozoite gliding motility, which, surprisingly, impacted neither their cell traversal capacity, host cell invasion in vitro, nor infectivity in vivo. Together, these data reveal a previously unappreciated complexity of the Plasmodiumsporozoite surface proteome and the roles of surface proteins in distinct biological activities of sporozoites.

ABSTRACTEvidence from clinical trials of malaria vaccine candidates suggests that both cell-mediated and humoral immunity to pre-erythrocytic parasite stages can provide protection against infection. Novel pre-erythrocytic antibody (Ab) targets could be key to improving vaccine formulations, which are currently based on targeting antigens such as the circumsporozoite protein (CSP). However, methods to assess the effects of sporozoite-specific Abs on pre-erythrocytic infection in vivoremain underdeveloped. Here, we combined passive transfer of monoclonal Abs (MAbs) or immune serum with a luciferase-expressing Plasmodium yoeliisporozoite challenge to assess Ab-mediated inhibition of liver infection in mice. Passive transfer of a P. yoeliiCSP MAb showed inhibition of liver infection when mice were challenged with sporozoites either intravenously or by infectious mosquito bite. However, inhibition was most potent for the mosquito bite challenge, leading to a more significant reduction of liver-stage burden and even a lack of progression to blood-stage parasitemia. This suggests that Abs provide effective protection against a natural infection. Inhibition of liver infection was also achieved by passive transfer of immune serum from whole-parasite-immunized mice. Furthermore, we demonstrated that passive transfer of a MAb against P. falciparumCSP inhibited liver-stage infection in a humanized mouse/P. falciparumchallenge model. Together, these models constitute unique and sensitive in vivomethods to assess serum-transferable protection against Plasmodiumsporozoite challenge.

Plasmodiumparasites infect the liver and replicate inside hepatocytes before they invade erythrocytes and trigger clinical malaria. Analysis of host signaling pathways affected by liver-stage infection could provide critical insights into host–pathogen interactions and reveal targets for intervention. Using protein lysate microarrays, we found that Plasmodium yoeliirodent malaria parasites perturb hepatocyte regulatory pathways involved in cell survival, proliferation, and autophagy. Notably, the prodeath protein p53 was substantially decreased in infected hepatocytes, suggesting that it could be targeted by the parasite to foster survival. Indeed, mice that express increased levels of p53 showed reduced liver-stage parasite burden, whereas p53 knockout mice suffered increased liver-stage burden. Furthermore, boosting p53 levels with the use of the small molecule Nutlin-3 dramatically reduced liver-stage burden in vitro and in vivo. We conclude that perturbation of the hepatocyte p53 pathway critically impacts parasite survival. Thus, host pathways might constitute potential targets for host-based antimalarial prophylaxis.