Protective humoral immunity elicited by a needle-free malaria vaccine comprised of a chimeric Plasmodium falciparum circumsporozoite protein and a Toll-like receptor 5 agonist, flagellin

Immunization with Plasmodium sporozoites can elicit high levels of sterile immunity, and neutralizing antibodies from protected hosts are known to target the repeat region of the circumsporozoite (CS) protein on the parasite surface. CS-based subunit vaccines have been hampered by suboptimal immunogenicity and the requirement for strong adjuvants to elicit effective humoral immunity. Pathogen-associated molecular patterns (PAMPs) that signal through Toll-like receptors (TLRs) can function as potent adjuvants for innate and adaptive immunity. We examined the immunogenicity of recombinant proteins containing a TLR5 agonist, flagellin, and either full-length or selected epitopes of the Plasmodium falciparum CS protein. Mice immunized with either of the flagellin-modified CS constructs, administered intranasally (i.n.) or subcutaneously (s.c.), developed similar levels of malaria-specific IgG1 antibody and interleukin-5 (IL-5)-producing T cells. Importantly, immunization via the i.n. but not the s.c. route elicited sporozoite neutralizing antibodies capable of inhibiting >90% of sporozoite invasion in vitro and in vivo, as measured using a transgenic rodent parasite expressing P. falciparum CS repeats. These findings demonstrate that functional sporozoite neutralizing antibody can be elicited by i.n. immunization with a flagellin-modified P. falciparum CS protein and raise the potential of a scalable, safe, needle-free vaccine for the 40% of the world's population at risk of malaria.

"Before we used to get sick all the time": perceptions of malaria and use of long-lasting insecticide-treated bed nets (LLINs) in a rural Kenyan community

Background

Malaria is a leading global cause of preventable morbidity and mortality, especially in sub-Saharan Africa, despite recent advances in treatment and prevention technologies. Scale-up and wide distribution of long-lasting insecticide-treated nets (LLINs) could rapidly decrease malarial disease in endemic areas, if used properly and continuously. Studies have shown that effective use of LLINs depends, in part, upon understanding causal factors associated with malaria. This study examined malaria beliefs, attitudes, and practices toward LLINs assessed during a large-scale integrated prevention campaign (IPC) in rural Kenya.

Methods

Qualitative interviews were conducted with 34 IPC participants who received LLINs as part of a comprehensive prevention package of goods and services. One month after distribution, interviewers asked these individuals about their attitudes and beliefs regarding malaria, and about their use of LLINs.

Results

Virtually all participants noted that mosquitoes were involved in causing malaria, though a substantial proportion of participants (47 percent) also mentioned an incorrect cause in addition to mosquitoes. For example, participants commonly noted that the weather (rain, cold) or consumption of bad food and water caused malaria. Regardless, most participants used the LLINs they were given and most mentioned positive benefits from their use, namely reductions in malarial illness and in the costs associated with its diagnosis and treatment.

Conclusions

Attitudes toward LLINs were positive in this rural community in Western Kenya, and respondents noted benefits with LLIN use. With improved understanding and clarification of the direct (mosquitoes) and indirect (e.g., standing water) causes of malaria, it is likely that LLIN use can be sustained, offering effective household-level protection against malaria.

Evaluation of various methods of maternal placental blood collection for immunology studies

The collection of maternal placental intervillous blood (IVB), without contamination of fetal blood and with an accurate mononuclear cell profile, is essential for immunological studies of placental malaria and other infectious diseases of the placenta. We have compared five documented methods of IVB collection: perfusion, incision, biopsy, tissue grinding, and puncture (prick) for fetal blood contamination and mononuclear cell profiles using flow cytometry. Twenty-five placentas were obtained from Plasmodium falciparum and human immunodeficiency virus-negative primigravid and secundigravid women delivering at Nyanza Provincial Hospital in Kisumu, western Kenya. Each of the five methods was performed on the same placenta. Fetal red blood cell contamination was significantly lower for the prick and perfusion methods (4.1% and 8.3%, respectively) than for incision (59.5%), biopsy (42.6%), and tissue grinding (19.9%). Significant variation was noted among the five methods in the percentages of monocytes, total T cells, CD4+ and CD8+ T cells, B cells, and NK cells. Further, a pairwise comparison of prick and perfusion, the two methods with low fetal blood contamination, showed that they were not different for fetal red blood cell contamination levels; however, prick yielded significantly higher percentages of CD4 T cells and CD4 memory T cells than perfusion. Collection by prick was determined to be the best method of intervillous blood collection for immunology studies, and perfusion represented the next best method of choice due to high sample volume yield. Overall, in considering the advantages/disadvantages of the two methods with low fetal cell contamination, we conclude that a combination of prick and perfusion is most suitable for immunology studies.

Immunohistological characterization of macrophage migration inhibitory factor expression in Plasmodium falciparum-infected placentas

Previously, we have shown that macrophage migration inhibitory factor (MIF) was highly elevated in the placental intervillous blood (IVB) of Plasmodium falciparum-infected women. Here, we compared the expression of MIF in placental tissues obtained from P. falciparum-infected and -uninfected women. Immunoperoxidase staining showed a consistent pattern of MIF expression in syncytiotrophoblasts, extravillous trophoblasts, IVB mononuclear cells, and amniotic epithelial cells, irrespective of their malaria infection status. Cytotrophoblast, villous stroma, and Hofbauer cells showed focal staining. Only amniotic epithelial and IVB mononuclear cells from P. falciparum-infected placentas exhibited significantly higher level of MIF expression than uninfected placentas. Stimulation of syncytilized human trophoblast BeWo cells with P. falciparum-infected erythrocytes that were selected to bind these cells resulted in significant increases in MIF secretion, whereas control erythrocytes, lipopolysaccharides, and synthetic beta-hematin had minimal effect. These findings suggest that placental malaria modulates MIF expression in different placental compartments.

Hemozoin differentially regulates proinflammatory cytokine production in human immunodeficiency virus-seropositive and -seronegative women with placental malaria

Pregnant women are at an increased risk for malarial infection. Plasmodium falciparum accumulates in the placenta and is associated with dysregulated immune function and poor birth outcomes. Malarial pigment (hemozoin) also accumulates in the placenta and may modulate local immune function. In this study, the impact of hemozoin on cytokine production by intervillous blood mononuclear cells from malaria-infected placentas was investigated. There was a dose-dependent, suppressive effect of hemozoin on production of gamma interferon (IFN-gamma), with less of an effect on tumor necrosis factor alpha (TNF-alpha) and interleukin-10, in human immunodeficiency virus-seronegative (HIV(-)) women. In contrast, IFN-gamma and TNF-alpha production tended to increase in HIV-seropositive women with increasing hemozoin levels. Production patterns of cytokines, especially IFN-gamma in HIV(-) women, followed different trends as a function of parasite density and hemozoin level. The findings suggest that the influences of hemozoin accumulation and high-density parasitemia on placental cytokine production are not equivalent and may involve different mechanisms, all of which may operate differently in the context of HIV infection. Cytokine production dysregulated by accumulation of hemozoin or high-density parasitemia may induce pathology and impair protective immunity in HIV-infected and -uninfected women.

Comparative flow cytometric analysis of term placental intervillous and peripheral blood from immediate postpartum women in Western kenya

Understanding maternal immune responses in the placenta is critical for management of pregnancy failures and haematogenous infections during pregnancy. However, it is unknown whether maternal placental intervillous blood (IVB) mononuclear cell populations are distinct from those found in maternal peripheral blood (PB). In this study, cell populations in the IVB and PB from immediate postpartum women were compared by flow cytometry. While levels of B and CD4+ and CD8+ T lymphocytes were similar, IVB contained significantly higher levels of monocytes (10.9+/-5.9 versus 5.5+/-2.5 per cent, respectively) and natural killer cells (14.3+/-9.6 versus 5.9+/-3.2 per cent, respectively) than the PB. Expression of the early activation marker CD69 was increased on T cells in the IVB, whereas levels of HLA-DR, a late activation marker, were similar between IVB and PB. These results suggest that maternal cells that circulate through the intervillous compartment may be subject to local influences that affect their distribution, phenotype and function. Further comparative study of these blood compartments will be necessary to elucidate the mechanisms by which the local placental milieu influences the IVB.

Levels of macrophage inflammatory protein 1 alpha (MIP-1 alpha) and MIP-1 beta in intervillous blood plasma samples from women with placental malaria and human immunodeficiency virus infection

Macrophage inflammatory protein-1 alpha (MIP-1 alpha) and MIP-1 beta play an important role in modulating immune responses. To understand their importance in immunity to placental malaria (PM) and in human immunodeficiency virus (HIV)-PM coinfection, we investigated levels of these chemokines in the placental intervillous blood plasma (IVB plasma) and cord blood plasma of HIV-negative PM-negative, HIV-negative PM-positive, HIV-positive PM-negative, and HIV-positive PM-positive women. Compared to HIV-negative PM-negative women, the MIP-1 beta concentration in IVB plasma was significantly elevated in HIV-negative PM-positive women and HIV-positive PM-positive women, but it was unaltered in HIV-positive PM-negative women. Also, PM-infected women, irrespective of their HIV status, had significantly higher levels of MIP-1 beta than HIV-positive PM-negative women. The MIP-1 alpha level was not altered in association with either infection. The IVB plasma levels of MIP-1 alpha and MIP-1 beta positively correlated with the cord blood plasma levels of these chemokines. As with IVB plasma, only cord plasma from PM-infected mothers had significantly elevated levels of MIP-1 beta compared to PM-negative mothers, irrespective of their HIV infection status. MIP-1 beta and MIP-1 alpha levels in PM-positive women were positively associated with parasite density and malaria pigment levels. Regardless of HIV serostatus, the IVB MIP-1 beta level was significantly lower in women with PM-associated anemia. In summary, an elevated level of MIP-1 beta was associated with PM. HIV infection did not significantly alter these two chemokine levels in IVB plasma.

Relationship between plasma Interleukin-12 (IL-12) and IL-18 levels and severe malarial anemia in an area of holoendemicity in western Kenya

In this study, we investigated whether levels of interleukin-12 (IL-12) and IL-18 in plasma are associated with severe malarial anemia outcomes in an area of holoendemicity in western Kenya. We compared plasma IL-12 and IL-18 levels in six groups of children grouped into the categories aparasitemic, asymptomatic, mild malaria, high-density uncomplicated malaria (UC), moderate malarial anemia (MMA), or severe malarial anemia (SMA). IL-12 levels were significantly reduced in children with SMA (P < 0.05) but not in other groups compared to children in the aparasitemic control group. IL-18, a cytokine known to be critical for the induction of gamma interferon along with IL-12, was produced more frequently (70%) in children with UC (P = 0.06) than in children in the aparasitemic control group (32%). However, in the SMA group the IL-18 response rate declined to 30%, which was similar to that in the aparasitemic control group, which showed a 32% response rate. This finding suggests that the IL-18 response may be impaired in children with SMA. In summary, the results from this study support the hypothesis that impairment of IL-12 and/or IL-18 response may contribute to the development of severe malarial anemia in areas of holoendemicity for malaria.

Immunity to placental malaria. IV. Placental malaria is associated with up-regulation of macrophage migration inhibitory factor in intervillous blood

Macrophage migration inhibitory factor (MIF) may play a role in immune responses to malaria during pregnancy by virtue of its ability to activate macrophages and to overcome the immunosuppressive effect of glucocorticoids. The present study investigated whether plasma MIF levels are altered in pregnant women with placental malaria (PM) and/or human immunodeficiency virus (HIV) infection. For the first time it is demonstrated that MIF levels in the intervillous blood (IVB) plasma were significantly elevated, compared with that in both peripheral plasma ( approximately 500-fold) and cord plasma (4.6-fold; P<.01). IVB mononuclear cells also produced significantly higher levels of MIF, compared with that of peripheral blood mononuclear cells. PM was associated with increased levels of MIF in the IVB plasma (P<.02). Primigravid and secundigravid women had significantly higher levels of MIF in their IVB plasma than did multigravid women (P<.05). HIV infection did not significantly alter MIF levels in any site examined.

A low interleukin-10 tumor necrosis factor-alpha ratio is associated with malaria anemia in children residing in a holoendemic malaria region in western Kenya

The balance between Th1 cytokines (tumor necrosis factor [TNF]-alpha, interferon [IFN]-gamma) and Th2 cytokines (interleukin [IL]-10, -4) may be critical in the development of severe falciparum malaria. Therefore, plasma concentrations of these cytokines were determined in children with various manifestations of malaria. Plasma levels of IFN-gamma and IL-4 were undetectable in most children. However, TNF-alpha and IL-10 were significantly elevated in children with high-density parasitemia and malaria anemia compared with children in control groups. In children with mild malaria, IL-10, but not TNF-alpha, was significantly elevated. While the highest concentrations of TNF-alpha were found in children with malaria anemia, IL-10 levels were highest in children with high-density uncomplicated malaria. The mean ratio of IL-10 to TNF-alpha was significantly higher in children with mild and high-density parasitemia (4.64, P<.005) than in children with malaria anemia (1.77). Thus, higher levels of IL-10 over TNF-alpha may prevent development of malaria anemia by controlling the excessive inflammatory activities of TNF-alpha.