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Introduction: Detailed analyses of genetic diversity, antigenic variability, protein localization and immunological responses are vital for the prioritization of novel malaria vaccine candidates. Comprehensive approaches to determine the most appropriate antigen variants needed to provide broad protection are challenging and consequently rarely undertaken. Methods: Here, we characterized PF3D7_1136200, which we named Asparagine-Rich Merozoite Antigen (ARMA) based on the analysis of its sequence, localization and immunogenicity. We analyzed IgG and IgM responses against the common variants of ARMA in independent prospective cohort studies in Burkina Faso (N = 228), Kenya (N = 252) and Mali (N = 195) using a custom microarray, Div-KILCHIP. Results: We found a marked population structure between parasites from Africa and Asia. African isolates shared 34 common haplotypes, including a dominant pair although the overall selection pressure was directional (Tajima's D = -2.57; Fu and Li's F = -9.69; P < 0.02). ARMA was localized to the merozoite surface, IgG antibodies induced Fc-mediated degranulation of natural killer cells and strongly inhibited parasite growth in vitro. We found profound serological diversity, but IgG and IgM responses were highly correlated and a hierarchical clustering analysis identified only three major serogroups. Protective IgG and IgM antibodies appeared to target both cross-reactive and distinct epitopes across variants. However, combinations of IgG and IgM antibodies against selected variants were associated with complete protection against clinical episodes of malaria. Discussion: Our systematic strategy exploits genomic data to deduce the handful of antigen variants with the strongest potential to induce broad protection and may be broadly applicable to other complex pathogens for which effective vaccines remain elusive. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are potent immune effectors that can be activated via antibody-mediated Fc receptor engagement. Using multiparameter flow cytometry, we found that NK cells degranulate and release IFN-γ upon stimulation with antibody-opsonized Plasmodium falciparum merozoites. Antibody-dependent NK (Ab-NK) activity was largely strain transcending and enhanced invasion inhibition into erythrocytes. Ab-NK was associated with the successful control of parasitemia after experimental malaria challenge in African adults. In an independent cohort study in children, Ab-NK increased with age, was boosted by concurrent P. falciparum infections, and was associated with a lower risk of clinical episodes of malaria. Nine of the 14 vaccine candidates tested induced Ab-NK, including some less well-characterized antigens: P41, P113, MSP11, RHOPH3, and Pf_11363200. These data highlight an important role of Ab-NK activity in immunity against malaria and provide a potential mechanism for evaluating vaccine candidates. A different antibody angle: Natural killer (NK) cells have been shown to mediate immune responses against Plasmodium falciparum using multiple effector functions. Odera et al. now show that antibody-opsonized P. falciparum merozoites can induce NK cell degranulation and IFN-γ production. This response was not strain specific and reduced invasion of merozoites into uninfected red blood cells. Using a controlled human malaria infection study in adults, they observed that antibody-dependent NK (Ab-NK) cell activity correlated directly with the control of parasitemia. In addition, in a cohort of children living in an endemic malaria setting, Ab-NK frequency increased with age, was boosted during P. falciparum infection, and was linked to a reduced risk of clinical malaria. These findings highlight a key role for antibody-mediated NK cell responses during malaria. —CF [ABSTRACT FROM AUTHOR]

Background: Health facility regulation in low- and middle-income countries (LMICs) is generally weak, with potentially serious consequences for safety and quality. Innovative regulatory reforms were piloted in three Kenyan counties including: a Joint Health Inspection Checklist (JHIC) synthesizing requirements across multiple regulatory agencies; increased inspection frequency; allocating facilities to compliance categories which determined warnings, sanctions and/or time to re-inspection; and public display of regulatory results. The reforms substantially increased inspection scores compared with control facilities. We developed lessons for future regulatory policy from this pilot by identifying key factors that facilitated or hindered its implementation. Methods: We conducted a qualitative study to understand views and experiences of actors involved in the one-year pilot. We interviewed 77 purposively selected staff from the national, county and facility levels. Data were analyzed using the framework approach, identifying facilitating/hindering factors at the facility, inspection system, and health system levels. Results: The joint health inspections (JHIs) were generally viewed as fair, objective and transparent, which enhanced their perceived legitimacy. Interactions with inspectors were described as friendly and supportive, in contrast to the punitive culture of previous inspections when bribery had been common. Inspector training and use of an electronic checklist were strongly praised. However, practical challenges with transport, route planning and budgets highlighted the critical nature of strong logistical management. The effectiveness of inspection in improving compliance was hampered by limitations in related systems, particularly facility licensing, enforcement of closures and, in the public sector, control of funds. However, an inclusive reform development process had led to high buy-in across regulatory agencies which was key to the system's success. Conclusion: Effective facility inspection involves more than "hardware" such as checklists, protocols and training. Cultural, relational and institutional "software" are also crucial for legitimacy, feasibility of implementation and enforceability, and should be carefully integrated into regulatory reforms. [ABSTRACT FROM AUTHOR]