Immunogenicity of the Plasmodium falciparum Pf332-DBL domain in combination with different adjuvants

Characterization of the Catalytic Subunits of the RNA Exosome-like Complex in Plasmodium falciparum

The eukaryotic ribonucleic acid (RNA) exosome is a versatile multiribonuclease complex that mediates the processing, surveillance, and degradation of virtually all classes of RNA in both the nucleus and cytoplasm. The complex, composed of 10 to 11 subunits, has been widely described in many organisms. Bioinformatic analyses revealed that there may be also an exosome‐like complex in Plasmodium falciparum, a parasite of great importance in public health, with eight predicted subunits having high sequence similarity to their counterparts in yeast and human. In this work, the putative RNA catalytic components, designated as PfRrp4, PfRrp41, PfDis3, and PfRrp6, were identified and systematically analyzed. Quantitative polymerase chain reaction (QPCR) analyses suggested that all of them were transcribed steadily throughout the asexual stage. The expression of these proteins was determined by Western blot, and their localization narrowed to the cytoplasm of the parasite by indirect immunofluorescence. The recombinant proteins of PfRrp41, PfDis3, and PfRrp6 exhibited catalytic activity for single‐stranded RNA (ssRNA), whereas PfRrp4 showed no processing activity of both ssRNA and dsRNA. The identification of these putative components of the RNA exosome complex opens up new perspectives for a deep understanding of RNA metabolism in the malarial parasite P. falciparum.

Three Novel Candidate Probiotic Strains with Prophylactic Properties in a Murine Model of Cow's Milk Allergy

Food allergies can have significant effects on morbidity and on quality of life. Therefore, the development of efficient approaches to reduce the risk of developing food allergies is of considerable interest. The aim of this study was to identify and select probiotic strains with preventive properties against allergies using a combination of in vitro and in vivo approaches. To that end, 31 strains of bifidobacteria and lactic acid bacteria were screened for their immunomodulatory properties in two cellular models, namely, human peripheral blood mononuclear cells (PBMCs) and T helper 2 (Th2)-skewed murine splenocytes. Six strains inducing a high interleukin-10 (IL-10)/IL-12p70 ratio and a low secretion of IL-4 on the two cellular models were selected, and their protective impact was tested in vivo in a murine model of food allergy to β-lactoglobulin. Three strains showed a protective impact on sensitization, with a decrease in allergen-specific IgE, and on allergy, with a decrease in mast cell degranulation. Analysis of the impact of these three strains on the T helper balance revealed different mechanisms of action. The Lactobacillus salivarius LA307 strain proved to block Th1 and Th2 responses, while the Bifidobacterium longum subsp. infantis LA308 strain induced a pro-Th1 profile and the Lactobacillus rhamnosus LA305 strain induced pro-Th1 and regulatory responses. These results demonstrate that a combination of in vitro and in vivo screening is effective in probiotic strain selection and allowed identification of three novel probiotic strains that are active against sensitization in mice.

The extracellular matrix protein mindin as a novel adjuvant elicits stronger immune responses for rBAG1, rSRS4 and rSRS9 antigens of Toxoplasma gondii in BALB/c mice

Background

Vaccines are the most effective agents to control infections. However, recombinant vaccines often do not elicit strong immune responses. Protein antigens combined with proper adjuvants have been widely used to induce immune responses, especially the humoral immune responses, against various pathogens, including parasites. The extracellular matrix protein mindin has been recognised as an immune facilitator for initiating innate immune responses. It has therefore been expected to be a potentially potent adjuvant in the development of novel vaccines. The aim of this study was to investigate whether mindin could facilitate the induction of antigen-specific immune responses to recombinant antigens (rBAG1, rSRS4 and rSRS9) of Toxoplasma gondii in BALB/c mice.

Methods

In this study, we explored the adjuvant effect of the recombinant mindin in the generation of specific Th1 and Th2 responses to each of three T. gondii antigens, BAG1, SRS4 and SRS9. All mice in the experimental groups received either antigen alone or in combination with Freund’s adjuvant or with the recombinant mindin. The immune responses after immunisation were measured by ELISA and lymphoproliferative assays. The immunised mice were challenged with live T. gondii tachyzoites, and the protection efficiency was compared between the groups.

Results

Our results revealed that mindin as an adjuvant could facilitate the recombinant proteins to efficiently stimulate humoral and cellular responses, including antigen-specific IgG1 and IgG2a, as well as lymphocyte proliferation. Furthermore, significantly improved protection against T. gondii infection was observed in the mindin group compared with that of Freund’s adjuvant and no-adjuvant groups.

Conclusions

The extracellular matrix protein mindin can effectively induce antigen-specific humoral and cell-mediated immune responses. Our study provides a valuable basis for the development of an efficient, safe, non-toxic vaccine adjuvant for future use in humans and animals.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-429) contains supplementary material, which is available to authorized users.

Pattern of antibodies to the Duffy binding like domain of Plasmodium falciparum antigen Pf332 in Senegalese individuals

Acquisition of antibodies against blood stage antigens is crucial in malaria immunity and the Plasmodium falciparum antigen Pf332, which is present in close association with the infected red blood cell membrane, is one such antigen. In this study, the antibody response to a Duffy binding like fragment of Pf332, termed Pf332-DBL was investigated in sera from naturally exposed individuals living in Dielmo village, Senegal, with regard to immunoglobulin classes (IgG, IgM, IgE) and IgG subclasses (IgG1-4). While the levels of IgM, IgG, IgG1 and IgG2 only displayed a moderate trend to increase with age, Pf332-DBL specific IgG3 levels increased significantly in the older villagers. In multivariate analysis, when controlling for confounding factors, and in a linear model with a Poisson distribution, anti-Pf332-DBL IgG3 as well as the ratio of cytophilic to non cytophilic anti-Pf332-DBL antibodies were found significantly associated with a reduced risk of malaria attack. This association was also present when the IgG3:IgG1 ratio was tested. Finally, two subgroups of villagers with the same mean age, were delineated by IgG3 concentrations either lower or higher than the median value. A total of 45.2% of the individuals with low anti-Pf332-DBL-IgG3 levels but only 21.4% of the villagers in the group with high levels of such antibodies had a clinical malaria attack during a period of 3 years of continuous follow-up after the blood sampling. In conclusion, Pf332-DBL induces naturally the acquisition of antibodies, and Pf332-DBL-specific IgG3 appears to be associated with protection against malaria in this endemic setting.

Plasmodium falciparum antigen 332 is a resident peripheral membrane protein of Maurer's clefts

During the intraerythrocytic development of Plasmodium falciparum, the malaria parasite remodels the host cell cytosol by inducing membranous structures termed Maurer's clefts and inserting parasite proteins into the red blood cell cytoskeleton and plasma membrane. Pf332 is the largest known asexual malaria antigen that is exported into the red blood cell cytosol where it associates with Maurer's clefts. In the current work, we have utilized a set of different biochemical assays to analyze the solubility of the endogenous Pf332 molecule during its trafficking from the endoplasmic reticulum within the parasite to the host cell cytosol. Solubilization studies demonstrate that Pf332 is synthesized and trafficked within the parasite as a peripheral membrane protein, which after export into the host cell cytosol associates with the cytoplasmic side of Maurer's clefts in a peripheral manner. By immunofluorescence microscopy and flow cytometry, we show that Pf332 persists in close association with Maurer's clefts throughout trophozoite maturation and schizogony, and does not become exposed at the host cell surface. Our data also indicate that Pf332 interacts with the host cell cytoskeleton, but only in very mature parasite stages. Thus, the present study describes Pf332 as a resident peripheral membrane protein of Maurer's clefts and suggests that the antigen participates in host cytoskeleton modifications at completion of the intraerythrocytic developmental cycle.