Hélène Jouin

Isolation and flow cytometric analysis of the free lymphomyeloid cells present in murine liver

Recruitment of circulating lymphomyeloid cells in the liver during infection often plays a critical role, mediating control or exacerbation of the pathogen growth. This paper describes a simple and rapid technique to recover these lymphomyeloid cells from a normal or an infected liver. After portal perfusion with saline buffer, the liver is gently dissociated on steel screens and the resulting cell population spun in 35% Percoll in 100 IU/ml Calciparine to remove all nuclei and cell debris: the recovery of a pure liver lymphomyeloid cell population is usually achieved in 40-60 min. Phenotypic and functional analysis could then be easily carried out on this cell population. This methodology was applied to normal mouse liver: flow cytometric analysis of the purified free lymphomyeloid cells showed the presence of T lymphocytes (46% +/- 3 with a CD4/CD8 ratio of 2.8), B lymphocytes (20% +/- 2 IgG and 30% IgM positive) and myelomonocytic cells (14% +/- 2 complement receptor type III positive).

A method to recover, enumerate and identify lymphomyeloid cells present in an inflammatory dermal site: a study in laboratory mice

We describe a new method to recover and study cells present in the dermis of mouse ear at homeostasis or after intradermal injection of disturbing agents (lipopolysaccharide or Listeria monocytogenes). The ears either left untreated or inoculated were handled and processed as culture explants of the dorsal and ventral leaflets, their dermal sides being spread on a buffered medium. Within this medium emigrate/sediment, with different kinetics: neutrophils, mononuclear phagocytes, dendritic leucocytes, T lymphocytes expressing either gamma delta or alpha beta TCRs, and other minor subsets, the identification of which deserves more relevant reagents: they are likely to be NK, mast cells, eosinophils and their local progenitors. All the major subsets were identified through a combination of immunocytochemical and flow cytometry labeling. Two examples illustrating the advantages and limitations of this new method are given: either 1 microgram of LPS or 10(4) Listeria monocytogenes were injected within the ear 48, 24, 12, 6, 3 h before ear explant culture. This ear explant culture has been further compared to the ear sheet treatment with collagenase/disease for three cell populations, the epidermal dendritic leucocytes, the gamma delta epidermal T cells as well as the alpha beta T cells recirculating within the steady state dermis. This method provides the first evidence of the existence of recirculating T CD4 lymphocytes in the mouse dermis.

Assessment of Plasmodium falciparum resistance to ferroquine (SSR97193) in field isolates and in W2 strain under pressure

BackgroundFerroquine (FQ), or SSR97193, is a novel antimalarial drug currently in phase I clinical trials. FQ is a unique organometallic compound designed to overcome the chloroquine (CQ) resistance problem. FQ revealed to be equally active on CQ-sensitive and CQ-resistant Plasmodium falciparum laboratory strains and field isolates. FQ is also curative on rodent malaria parasites. As FQ will be tested in patients, the potential for resistance to this drug was evaluated.MethodsThe relationship between CQ-resistant transporter gene genotype and susceptibility to FQ were studied in 33 Cambodian P. falciparum field isolates previously studied for their in vitro response to CQ. In parallel, the ability of the CQ-resistant strain W2, to become resistant to FQ under drug pressure was assessed.ResultsThe IC50 values for FQ in field isolates were found to be unrelated to mutations occurring in the P. falciparum chloroquine resistance transporter (PfCRT) or to the level of expression of the corresponding mRNA. In vitro, under a drug pressure of 100 nM of FQ, transient survival was observed in only one of two experiments.ConclusionField isolates studies and experimental drug pressure experiments showed that FQ overcomes CQ resistance, which reinforces the potential of this compound as a new antimalarial drug.

Regulation of Antigen-Specific Immunoglobulin G Subclasses in Response to Conserved and Polymorphic Plasmodium falciparum Antigens in an In Vitro Model

ABSTRACT Cytophilic antibodies (Abs) play a critical role in protection against Plasmodium falciparum blood stages, yet little is known about the parameters regulating production of these Abs. We used an in vitro culture system to study the subclass distribution of antigen (Ag)-specific immunoglobulin G (IgG) produced by peripheral blood mononuclear cells (PBMCs) from individuals exposed to P. falciparum or unexposed individuals. PBMCs, cultivated with or without cytokines and exogenous CD40/CD40L signals, were stimulated with a crude parasite extract, recombinant vaccine candidates derived from conserved Ags (19-kDa C terminus of merozoite surface protein 1 [MSP119], R23, and PfEB200), or recombinant Ags derived from the polymorphic Ags MSP1 block 2 and MSP2. No P. falciparum-specific Ab production was detected in PBMCs from unexposed individuals. PBMCs from donors exposed frequently to P. falciparum infections produced multiple IgG subclasses when they were stimulated with the parasite extract but usually only one IgG subclass when they were stimulated with a recombinant Ag. Optimal Ab production required addition of interleukin-2 (IL-2) and IL-10 for all antigenic preparations. The IgG subclass distribution was both donor and Ag dependent and was only minimally influenced by the exogenous cytokine environment. In vitro IgG production and subclass distribution correlated with plasma Abs to some Ags (MSP119, R23, and MSP2) but not others (PfEB200 and the three MSP1 block 2-derived Ags). Data presented here suggest that intrinsic properties of the protein Ag itself play a major role in determining the subclass of the Ab response, which has important implications for rational design of vaccine delivery.

Plasmodium falciparum merozoite surface protein 1 (MSP1): genotyping and humoral responses to allele-specific variants.

The present study is the first to investigate Plasmodium falciparum merozoite surface protein 1 (MSP1) allele-specific humoral responses in residents of central Africa. In endemic areas, acquired immune responses to malaria are assumed to reflect the need to be infected with a large number of antigenically diverse parasite populations. In the work presented here, the relationship between antibody specificity and the infecting parasite genotype was investigated in asymptomatic subjects and patients with uncomplicated malaria in order to possibly clarify the relationship between anti-MSP1 block2 antibodies and clinical malaria. Overall isolates were typed by nested PCR using allele-specific primers of the P. falciparum MSP1 gene to identify the infecting parasite genotype. The K1 type was the predominant allelic family in both clinical groups. Polyinfection (number of isolates with more than one parasite genotype) and the complexity of infections (mean number of parasite genotype per infected subject) were higher in isolates from asymptomatic individuals. Total immunoglobulins G (IgG) responses to schizont crude extract antigens and to MSP1 variant-specific peptides were assessed by ELISA test. More than 90% of the sera reacted against schizont extract, whatever the clinical group and the K1 seroprevalence was the highest in both clinical groups. Our results showed an age-dependence in the number of different variants of MSP1 block2 recognised by serum. Indeed, isolates from older (>14 years) subjects showed lower multiplicity of infection and higher was the mean number of different MSP1 variants recognised by their serum. This corresponded to the age reported for the acquisition of anti-parasite immunity under high malaria endemicity. The contribution of variant-specific immunity in asymptomatic malaria infections is discussed.

Fixed, epitope-specific, cytophilic antibody response to the polymorphic block 2 domain of the Plasmodium falciparum merozoite surface antigen MSP-1 in humans living in a malaria-endemic area.

The MSP‐1 merozoite surface antigen of the human malaria parasite Plasmodium falciparum is a major target of immune response. The domain called block 2 shows extensive allelic diversity, with more than 50 alleles identified, grouped into three allelic families. Presence of anti‐block 2 antibodies has been associated with reduced risk for clinical malaria, but whether or not allele‐specific antibodies are implicated remains unclear. To study the fine specificity of the human antibody response, we have used a series of 82 overlapping, N‐biotinylated, 15‐mer peptides scanning reference alleles and including numerous sequence variants. Peptide antigenicity was validated using sera from mice immunized with recombinant proteins. A cross‐sectional survey conducted in a Senegalese village with intense malaria transmission indicated an overall 56 % seroprevalence. The response was specific for individuals and unrelated to the HLA type. Each responder reacted to a few peptides, unrelated to the infecting parasite genotype(s). Seroprevalence of each individual peptide was low, with no identifiable immunodominant epitope. Anti‐block 2 antibodies were mostly of the IgG3 isotype, consistent with an involvement in cytophilic antibody‐mediated merozoite clearance. The number of responders increased with age, but there was no accumulation of novel specificities with age and hence with exposure to an increasingly large number of alleles. A 15‐month longitudinal follow up outlined a remarkably fixed response, with identical reactivity profiles, independent of the past or current parasite types, a pattern reminiscent of clonal imprinting. The implications of the characteristics of the anti‐block 2 antibody response in parasite clearance are discussed.

Plasmodium falciparum: Molecular analysis of a putative protective antigen, the thermostable 96-kDa protein

A group of three Plasmodium falciparum antigens of distinct pI, migrating with an apparent MW of 96 kDa has been previously identified as a target of protective immunity both in humans and in monkeys (Jouin et al. 1987, Dubois et al. 1987). These antigens are produced during the late stages of asexual intraerythrocytic development. One of these 96-kDa proteins, the 96 tR, has a pI of 5.25, is thermostable, and is released in the culture supernatant (Jouin et al. 1987). We report here the cloning and expression in Escherichia coli of the gene coding for this antigen. Antibodies raised to the recombinant 96 tR immunoprecipitated exclusively the 96 tR, indicating that the other two antigens of 96 kDa are the product(s) of distinct gene(s). Northern and Southern blots as well as DNA sequencing of the gene showed that the 96 tR antigen is identical to proteins identified in other laboratories as the glycophorin binding protein GBP 130 (Perkins 1984, Ravetch et al. 1985) and Ag 78 (Bianco et al. 1987). The 96-kDa antigen is produced at the trophozoite stage and more actively in the schizonts. It is released in the culture supernatant at the time of schizont rupture, together with two minor products, forming a characteristic triplet. This triplet was also detected in immunoblots of merozoites. An approximate quantification on immunoblots indicated that the largest proportion of the protein is found in the culture supernatant, a minor fraction being loosely associated with merozoites. By immunofluorescence and immunoelectron microscopy, intense signals were observed in the erythrocyte cytoplasm. The 50-amino acid repeats were found in all strains examined, the protein showing some size polymorphism. The antigen was detected in the serum of infected monkeys as well as in that of infected humans.

Double staining of Plasmodium falciparum nucleic acids with hydroethidine and thiazole orange for cell cycle stage analysis by flow cytometry.

Microarray analyses of stage‐specific gene expression of Plasmodium falciparum require purification of RNAs from highly synchronized cultures. To date, no reliable method to control the quality of synchronization of P. falciparum cultures is available.

Flow cytometry detection of surface antigens on fresh, unfixed red blood cells infected by Plasmodium falciparum

The immunofluorescence detection of parasite-specific antigens on the surface of red blood cells infected by Plasmodium falciparum parasites is usually performed by visual detection under a fluorescence microscope. We describe here a technique permitting the analysis of surface immunofluorescence labelling by flow cytometry. Infected red blood cells are selected on the basis of their parasitic DNA and RNA content by Hoechst and Thiazole Orange vital dyes. Cytometric analysis of these labels, as well as general erythrocyte characteristics assessed by analysis of forward and side scatter allows the selection of viable intact infected erythrocytes from other blood cells. The integrity of these selected erythrocytes was confirmed by the absence of labelling with antibodies directed against internal components such as spectrin. This technique permits the detection of specific surface immunofluorescence staining on red blood cells infected with mature stages of P. falciparum by antibodies in sera from hyperimmune Saimiri monkeys. Using Thiazole Orange dye for detection of parasitised cells, this analysis was performed on a FACSscan apparatus equipped with a single laser.

Regulation of protein phosphatase type 1 and cell cycle progression by PfLRR1, a novel leucine-rich repeat protein of the human malaria parasite Plasmodium falciparum.

The protein called ‘suppressor of the dis2 mutant (sds22+)’ is an essential regulator of cell division in fission and budding yeasts, where its deletion causes mitotic arrest. Its role in cell cycle control appears to be mediated through the activation of protein phosphatase type 1 (PP1) in Schizosaccharomyces pombe. We have identified the Plasmodium falciparum Sds22 orthologue, which we designated PfLRR1 as it belongs to the leucine‐rich repeat protein family. We showed by glutathione‐S‐transferase pull‐down assay that the PfLRR1 gene product interacts with PfPP1, that the PfLRR1–PfPP1 complex is present in parasite extracts and that PfLRR1 inhibits PfPP1 activity. Functional studies in Xenopus oocytes revealed that PfLRR1 interacted with endogenous PP1 and overcame the G2/M cell cycle checkpoint by promoting progression to germinal vesicle breakdown (GVBD). Confirmatory results showing the appearance of GVBD were observed when oocytes were treated with anti‐PP1 antibodies or okadaic acid. Taken together, these observations suggest that PfLRR1 can regulate the cell cycle by binding to PP1 and regulating its activity.