[Show abstract][Hide abstract] ABSTRACT: Trees belonging to the order of Fagales show a distinct geographical distribution. While alder and birch are endemic in the temperate zones of the Northern hemisphere, hazel, hornbeam, and oak prefer a warmer climate. However, specific immunotherapy of Fagales pollen allergic patients is mainly performed using birch pollen extracts, thus limiting the success of this intervention in birch-free areas.
T cells are considered key players in the modification of an allergic immune response during SIT, therefore we thought to combine linear T cell epitope-containing stretches of the five most important Fagales allergens from birch, hazel, alder, oak, and hornbeam resulting in a Fagales pollen hybrid molecule (FPH) applicable for SIT.
FPH was generated by PCR-based recombination of low IgE-binding allergen epitopes. Moreover, a structural-variant PH4 was calculated by in silico mutagenesis, rendering the protein unable to adopt the Bet v 1-like fold. Both molecules were produced in E. coli, characterized physico-chemically as well as immunologically and tested in mouse models of allergic sensitization as well as allergy prophylaxis.
Using spectroscopic analyses both proteins were monomeric, the secondary structure elements of FPH resemble the ones typical for Bet v 1-like proteins, whereas FPH4 showed increased amounts of unordered structure. Both molecules displayed reduced binding capacities of Bet v 1-specific IgE antibodies. However, in a mouse model the proteins were able to induce high IgG titers cross-reactive with all parental allergens. Moreover, prophylactic treatment with the hybrid proteins prevented pollen extract-induced allergic lung inflammation in vivo.
The hybrid molecules showed a more efficient uptake and processing by dendritic cells resulting in a modified T cell response. The proteins had a lower IgE-binding capacity compared to the parental allergens, thus the high safety profile and increased efficacy emphasizes clinical application for the treatment of Fagales multi-sensitization. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: In Austria the vaccination coverage among health care workers (HCW) - particularly among hospital personnel - is not sufficient. This is of specific concern, because not only the individual protection but also the prevention of disease transmission of vaccine preventable diseases between HCW and patients needs to be guaranteed. Particularly immunosuppressed patients, who are at higher risk for morbidity and mortality due to certain infections, but cannot be vaccination themselves, must be able to rely on herd protection, i.e. not being infected by surrounding/caring persons.The following publication provides for the first time detailed guidelines for vaccination programs for HCWs in Austria, including personnel within hospitals, medical institutions and laboratories, as well as Medical Universities including students. Moreover, these guidelines are also recommended to medical personnel in outpatient clinics, social service institutions and medical practices.Additionally to the vaccination schedules this publication also includes a chapter on ethical as well as legal background underlying these recommendations.
Wiener klinische Wochenschrift 11/2013; · 0.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a prospective surveillance study covering all pediatric wards in Austria, 308 cases of invasive pneumococcal disease (IPD) were reported in hospitalized children <5 years of age between 2002 and 2012. Incidence was 7.1 per 100,000 per year for IPD with a case fatality rate of 3 %, and 1.9 per 100,000 per year for pneumococcal meningitis with a case fatality rate of 9 %. At hospital discharge, 17 % of the children were not fully recovered and suffered from problems such as hearing or motor deficits. Persistent sequelae 6 months after hospital discharge were present in 13 % of the children, a finding that emphasizes the seriousness of IPD. From 2007 onwards, we observed a shift of pneumococcal serotypes from those covered by the heptavalent vaccine to serotypes consequently added to 10- and 13-valent vaccines, particularly regarding serotype 19A. Among antimicrobial resistances detected, macrolide resistance was predominant; however, between 2002 and 2012, we saw an overall decrease of resistance rates. Conclusion: Considering this change of serotypes and the high rate of permanent sequelae after IPD, our data show the importance of pediatric pneumococcal vaccination and the relevance of continuous monitoring of circulating serotypes. By the end of 2012, which was the first year of universal mass vaccination against pneumococcal disease in Austria, no change in the incidence of invasive pneumococcal disease was observed yet.
European Journal of Pediatrics 11/2013; · 1.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The main goal in reversing the allergy epidemic is the development of effective prophylactic strategies. We investigated the prophylactic effect of neonatal mother-to-offspring mono-colonization with Bifidobacterium longum ssp. longum CCM 7952 on subsequent allergic sensitization. Adult male and female germ-free (GF) mice were mono-colonized with B. longum, mated and their offspring, as well as age-matched GF controls, were sensitized with the major birch pollen allergen Bet v 1. Furthermore, signaling pathways involved in the recognition of B. longum were investigated in vitro. Neonatal mono-colonization of GF mice with B. longum suppressed Bet v 1-specific IgE-dependent β-hexosaminidase release as well as levels of total IgE and allergen-specific IgG2a in serum compared to sensitized GF controls. Accordingly, Bet v 1-induced production of both Th1- and Th2-associated cytokines in spleen cell cultures was significantly reduced in these mice. The general suppression of Bet v 1-specific immune responses in B. longum colonized mice was associated with increased levels of regulatory cytokines IL-10 and TGF-β in serum. In vitro, B. longum induced low maturation status of bone marrow-derived dendritic cells and production of IL-10 in TLR2-, MyD88-, and MAPK-dependent manner. Our data demonstrate that neonatal mono-colonization with B. longum reduces allergic sensitization, likely by activation of regulatory responses via TLR2, MyD88, and MAPK signaling pathways. Thus, B. longum might be a promising candidate for perinatal intervention strategies against the onset of allergic diseases in humans.
[Show abstract][Hide abstract] ABSTRACT: Low responsiveness/nonresponsiveness is characterized by an insufficient immune response upon primary and/or booster vaccination and affects 1-10% of vaccinees. In the current study, we aimed to investigate whether nonresponsiveness is an Ag/vaccine-specific phenomenon and to clarify underlying immunological mechanisms. Nonresponders to tick-borne encephalitis (TBE) or hepatitis B Ag with a history of previous TBE vaccinations were booster vaccinated with TBE and influenza vaccine and compared with TBE high responders in terms of humoral and cellular immune response. Postboosters in TBE high responder existing TBE titers increased, and solid humoral responses to influenza vaccine were induced. In TBE nonresponders, low to undetectable prevaccination TBE titers remained low, whereas sufficient influenza Abs were induced. In both TBE groups, a positive correlation of humoral and cellular immune response was seen as high/low TBE titers were associated with sufficient/lack of Ag-specific T cell proliferation. Furthermore, responses to influenza were robust in terms of Abs and cytokine production. In contrast, in hepatitis B nonresponders, sufficient humoral responses to TBE and influenza Ags were induced despite lacking specific IL-2 and IFN-γ production. Importantly, these patients showed high IL-10 baseline levels in vitro. HLA-DR subtypes associated with hepatitis B nonresponsiveness were overrepresented in this group, and high IL-10 levels were linked to these subtypes. Whereas TBE and hepatitis B nonresponders had increased IL-10-producing FOXP3(+) T regulatory cells upon vaccination, only in hepatitis B nonresponders, showing elevated prevaccination IL-10 levels, a prominent population of B regulatory cells was detected. We conclude that immunological pathways of nonresponsiveness follow different patterns depending both on vaccine Ag and genetic predisposition of the vaccinee.
The Journal of Immunology 07/2013; · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Immunologic interventions in a subset of breast cancer patients represent a well-established therapeutic approach reflecting individualized treatment modalities. Thus, the therapeutic administration of monoclonal antibodies targeting tumor-associated antigens (TAA), such as Her-2/neu, represents a milestone in cancer treatment. However, passive antibody administration suffers from several drawbacks, including frequency and long duration of treatment. These undesirables may be avoidable in an approach based on generating active immune responses against these same targets. Only recently has the significance of tumors in relation to their microenvironments been understood as essential for creating an effective cancer vaccine. In particular, the immune system plays an important role in suppressing or promoting tumor formation and growth. Therefore, activation of appropriate triggers (such as induction of Th1 cells, CD8+ T cells, and suppression of regulatory cells in combination with generation of antibodies with anti-tumor activity) is a desirable goal. Current vaccination approaches have concentrated on therapeutic vaccines using certain TAA. Many cancer antigens, including breast cancer antigens, have been described and also given priority ranking for use as vaccine antigens by the US National Cancer Institute. One of the TAA antigens which has been thoroughly examined in numerous trials is Her-2/neu. This review will discuss delivery systems for this antigen with special focus on T and B cell peptide vaccines. Attention will be given to their advantages and limitations, as well as the use of certain adjuvants to improve anti-cancer responses.
Breast Cancer Research and Treatment 01/2013; · 4.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a sample of originally 430 healthy adults (18-84 years of age) with documented basic and booster immunization against tick borne encephalitis, cumulative seroprotection rates 8 (n=178) and 10 years (n=183) after the last booster dose were 86.8% and 77.3% according to the neutralization test, respectively. In subjects aged 50 years and older, antibody titers were significantly lower compared to subjects younger than 50 years. History of any allergy but not previous exposure to other flaviviral antigens was associated with higher neutralization titers. In subjects with waning immunity, a single booster dose induced a strong anamnestic antibody response.
[Show abstract][Hide abstract] ABSTRACT: One third of the human population is currently infected by one or more species of parasitic helminths. Certain helminths establish long-term chronic infections resulting in a modulation of the host's immune system with attenuated responsiveness to "bystander" antigens such as allergens or vaccines. In this study we investigated whether parasite-derived products suppress the development of allergic inflammation in a mouse model. We show that extract derived from adult male Oesophagostomum dentatum (eMOD) induced Th2 and regulatory responses in BALB/c mice. Stimulation of bone marrow-derived dendritic cells induced production of regulatory cytokines IL-10 and TGF-beta. In a mouse model of birch pollen allergy, co-administration of eMOD with sensitizing allergen Bet v 1 markedly reduced the production of allergen-specific antibodies in serum as well as IgE-dependent basophil degranulation. Furthermore, eMOD prevented the development of airway inflammation, as demonstrated by attenuation of bronchoalveolar lavages eosinophil influx, peribronchial inflammatory infiltrate, and mucus secretion in lungs and IL-4 and IL-5 levels in lung cell cultures. Reduced secretion of Th2-related cytokines by birch pollen-re-stimulated splenocytes and mesenteric lymph node cells was observed in eMOD-treated/sensitized and challenged mice in comparison to sensitized and challenged controls. The suppressive effects of eMOD were heat-stable. Immunization with model antigens in the presence of eMOD reduced production of antibodies to thymus-dependent but not to thymus-independent antigen, suggesting that suppression of the immune responses by eMOD was mediated by interference with antigen presenting cell or T helper cell function but did not directly suppress B cell function. In conclusion, we have shown that eMOD possesses immunomodulatory properties and that heat-stable factors in eMOD are responsible for the dramatic suppression of allergic responses in a mouse model of type I allergy. The identification and characterization of parasite-derived immune-modulating molecules might have potential for designing novel prophylactic/therapeutic strategies for immune-mediated diseases.
PLoS ONE 01/2013; 8(7):e67544. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: IgE antibody-mediated allergies affect more than 25% of the population worldwide. To investigate therapeutic and preventive effects of passive immunization with allergen-specific IgG antibodies on allergy in mouse models we used clinically relevant pollen allergens. In a treatment model, mice were sensitized to the major birch pollen allergen Bet v 1 and to the major grass pollen allergens, Phl p 1 and Phl p 5 and then received passive immunization with rabbit IgG antibodies specific for the sensitizing or an unrelated allergen. In a prevention model, mice obtained passive immunization with allergen-specific rabbit IgG before sensitization. Kinetics of the levels of administered IgG antibodies, effects of administered allergen-specific IgG on allergen-specific IgE reactivity, the development of IgE and IgG responses and on immediate allergic reactions were studied by ELISA, rat basophil leukaemia degranulation assays and skin testing, respectively. Treated mice showed an approximately 80% reduction of allergen-specific IgE binding and basophil degranulation which was associated with the levels of administered allergen-specific IgG antibodies. Preventive administration of allergen-specific IgG antibodies suppressed the development of allergen-specific IgE and IgG(1) antibody responses as well as allergen-induced basophil degranulation and skin reactivity. Our results show that passive immunization with allergen-specific IgG antibodies is effective for treatment and prevention of allergy to clinically important pollen allergens in a mouse model and thus may pave the road for the clinical application of allergen-specific antibodies in humans.
[Show abstract][Hide abstract] ABSTRACT: Travelers' diarrhea (TD) is the most important health issue among international travelers. In high risk areas, 50-90% of travelers may experience an episode of TD. The risk of acquiring TD is influenced by factors such as the destination, duration of stay, standard of accommodation, type of travel, age of the traveler, and also by individual risk factors. Most cases of TD are caused by bacteria; treatment for TD are loperamide and antibiotics. Preventive strategies such as hygiene measures have limited impact. Prophylactic intake of antibiotics or vaccines to prevent from TD can be considered in special situations.
Infectious disease clinics of North America 09/2012; 26(3):691-706. · 2.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Indianmeal moth Plodia interpunctella is a highly prevalent food pest in human dwellings, and has been shown to contain a number of allergens. So far, only one of these, the arginine kinase (Plo i 1) has been identified.
The aim of this study was to identify further allergens and characterise these in comparison to Plo i 1.
A cDNA library from whole adult P. interpunctella was screened with the serum of a patient with indoor allergy and IgE to moths, and thioredoxin was identified as an IgE-binding protein. Recombinant thioredoxin was generated in E. coli, and tested together with Plo i 1 and whole moth extracts in IgE immunoblots against a large panel of indoor allergic patients' sera. BALB/c mice were immunised with recombinant thioredoxin and Plo i 1, and antibody production, mediator release from RBL cells, T-cell proliferation and cytokine production were measured.
For the first time a thioredoxin from an animal species was identified as allergen. About 8% of the sera from patients with IgE against moth extracts reacted with recombinant P. interpunctella thioredoxin, compared to 25% reacting with recombinant Plo i 1. In immunised BALB/c mice, the recombinant allergens both induced classical Th2-biased immune responses such as induction IgE and IgG1 antibodies, upregulation of IL-5 and IL-4 and basophil degranulation.
Thioredoxin from moths like Plo i 1 acts like a classical Type I allergen as do the thioredoxins from wheat or corn. This clearly supports the pan-allergen nature of thioredoxin. The designation Plo i 2 is suggested for the new P. interpunctella allergen.
PLoS ONE 01/2012; 7(7):e42026. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The hygiene hypothesis implies that microbial agents including probiotic bacteria may modulate foetal/neonatal immune programming and hence offer effective strategies for primary allergy prevention; however their mechanisms of action are poorly understood. We investigated whether oral administration of Lactobacillus paracasei NCC 2461 to mothers during gestation/lactation can protect against airway inflammation in offspring in a mouse model of birch pollen allergy, and examined the immune mechanisms involved.
BALB/c mice were treated daily with L. paracasei in drinking water or drinking water alone in the last week of gestation and during lactation. Their offspring were sensitized with recombinant Bet v 1, followed by aerosol challenge with birch pollen extract.
Maternal exposure to L. paracasei prevented the development of airway inflammation in offspring, as demonstrated by attenuation of eosinophil influx in the lungs; reduction of IL-5 levels in bronchoalveolar lavage, and in lung and mediastinal lymph node cell cultures; and reduced peribronchial inflammatory infiltrate and mucus hypersecretion. While allergen-specific IgE and IgG antibody levels remained unchanged by the treatment, IL-4 and IL-5 production in spleen cell cultures were significantly reduced upon allergen stimulation in offspring of L. paracasei treated mice. Offspring of L. paracasei supplemented mothers had significantly reduced Bet v 1-specific as well as Concanavalin A-induced responses in spleen and mesenteric lymph node cell cultures, suggesting the modulation of both antigen-specific and mitogen-induced immune responses in offspring. These effects were associated with increased Foxp3 mRNA expression in the lungs and increased TGF-beta in serum.
Our data show that in a mouse model of birch pollen allergy, perinatal administration of L. paracasei NCC 2461 to pregnant/lactating mothers protects against the development of airway inflammation in offspring by activating regulatory pathways, likely through TLR2/4 signalling.
PLoS ONE 01/2012; 7(7):e40271. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Among birch pollen allergic patients up to 70% develop allergic reactions to Bet v 1-homologue food allergens such as Api g 1 (celery) or Dau c 1 (carrot), termed as birch pollen-related food allergy. In most cases, specific immunotherapy with birch pollen extracts does not reduce allergic symptoms to the homologue food allergens. We therefore genetically engineered a multi-allergen chimer and tested if mucosal treatment with this construct could represent a novel approach for prevention of birch pollen-related food allergy.
BALB/c mice were poly-sensitized with a mixture of Bet v 1, Api g 1 and Dau c 1 followed by a sublingual challenge with carrot, celery and birch pollen extracts. For prevention of allergy sensitization an allergen chimer composed of immunodominant T cell epitopes of Api g 1 and Dau c 1 linked to the whole Bet v 1 allergen, was intranasally applied prior to sensitization.
Intranasal pretreatment with the allergen chimer led to significantly decreased antigen-specific IgE-dependent β-hexosaminidase release, but enhanced allergen-specific IgG2a and IgA antibodies. Accordingly, IL-4 levels in spleen cell cultures and IL-5 levels in restimulated spleen and cervical lymph node cell cultures were markedly reduced, while IFN-γ levels were increased. Immunomodulation was associated with increased IL-10, TGF-β and Foxp3 mRNA levels in NALT and Foxp3 in oral mucosal tissues. Treatment with anti-TGF-β, anti-IL10R or anti-CD25 antibodies abrogated the suppression of allergic responses induced by the chimer.
Our results indicate that mucosal application of the allergen chimer led to decreased Th2 immune responses against Bet v 1 and its homologue food allergens Api g 1 and Dau c 1 by regulatory and Th1-biased immune responses. These data suggest that mucosal treatment with a multi-allergen vaccine could be a promising treatment strategy to prevent birch pollen-related food allergy.
PLoS ONE 01/2012; 7(6):e39409. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Excepting tropical Africa, where Plasmodium falciparum prevails, Plasmodium vivax is the most frequent cause of malaria in Asia and Latin America. First reliable reports of chloroquine resistance came in 1989 from the area of the distribution of the Chesson-strain of P. vivax. Since then, reports also came from other areas of the world. This study had the objective of measuring the sensitivity of P.vivax to chloroquine and potential alternative compounds in western Thailand. The study was performed in 2008 in Mae Sot, Tak Province, and followed the method of Tasanor. The IC(50) and IC(90) values for chloroquine were 167 nM and 5445 nM, those for mefloquine were 139 nM and 5282 nM, those for artemisinin were 32 nM and 466 nM, and those for atovaquone 30 nM and 650 nM. The values for chloroquine indicate the existing or imminent occurrence of specific resistance. High prevalence of mefloquine resistance precludes its alternative use. However, atovaquone, in combination with proguanil, may be a possible alternative.
[Show abstract][Hide abstract] ABSTRACT: The IgE-mediated and Th2-dependent late-phase reaction remains a mechanistically enigmatic and daunting element of human allergic inflammation. In this study, we uncover the FcεRI on dendritic cells (DCs) as a key in vivo component of this form of allergy. Because rodent, unlike human, DCs lack FcεRI, this mechanism could be revealed only by using a new transgenic mouse model with human-like FcεRI expression on DCs. In the presence of IgE and allergen, FcεRI(+) DCs instructed naive T cells to differentiate into Th2 cells in vitro and boosted allergen-specific Th2 responses and Th2-dependent eosinophilia at the site of allergen exposure in vivo. Thus, FcεRI on DCs drives the cascade of pathogenic reactions linking the initial allergen capture by IgE with subsequent Th2-dominated T cell responses and the development of late-phase allergic tissue inflammation.
The Journal of Immunology 07/2011; 187(1):164-71. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the proficiency of the Austrian childhood vaccination schedule to induce long lasting seroprotection against vaccine preventable diseases a seroepidemiological study in 348 children between four and eight years of age was conducted. Antibodies against diphtheria, tetanus, pertussis, hepatitis B, measles, mumps and rubella antigens were assessed in children, who had been vaccinated with hexavalent DTaP-HBV-IPV/Hib vaccines at three, four, five months and in the second year of life and/or MMR vaccines in the second year of life at least once, but mostly twice. High seroprotection rates (SPRs) were detected for tetanus (96%) and measles (90%). SPRs regarding diphtheria and mumps were 81% and 72%, respectively. Rubella-SPRs were 68% in females and 58% in males. Hepatitis B-antibody levels ≥10 mIU/mL were present in 52%; antibodies against pertussis were detected in 27% of the children. SPRs for measles and rubella depended on the interval since last vaccination; mumps-antibodies were significantly lower after one MMR-vaccination only. Antibodies against diphtheria, tetanus and pertussis depended on the interval since last vaccination while HBs-antibodies did not. The low levels of antibodies 1-7 years after vaccination against pertussis, rubella and mumps after only one vaccination should be considered when recommending new vaccination schedules.
[Show abstract][Hide abstract] ABSTRACT: We compared the immunomodulatory properties of Bifidobacterium longum NCC 3001 and Lactobacillus paracasei NCC 2461 in a mouse model of poly-sensitization to birch and grass pollen allergens. Mucosal application of both strains at the time of sensitization and challenge led to significant suppression of airway inflammation and down-regulated allergen-specific immune responses. In contrast, in the mice treated with probiotics prior to sensitization and challenge, only B. longum displayed protective effects. Our findings stress that the choice of probiotic strain and the timing of the application are crucial for tolerance induction. Furthermore, this is the first demonstration of anti-allergic effects of probiotic bacteria in poly-sensitized mice.
[Show abstract][Hide abstract] ABSTRACT: In consideration of comprehensive and well-established vaccination programmes in industrialized countries, it is expected that immunity against tetanus among expectant mothers and their offspring is complete. Our study evaluated seroprotection against tetanus among newborns in Austria, who may gain passive immunity by transplacental transfer of maternal tetanus antibody.
Cord blood samples from 99 deliveries were analyzed for antibody concentration against tetanus toxoid by standardized ELISA.
85/99 (85.8%) individuals presented with levels of tetanus immunity having a protective antibody concentration ≥0.1 IU/ml. 9/99 (9.1%) samples showed low seropositivity, while in 5/99 (5.1%) samples no tetanus antibodies could be detected. The median antibody concentration was 0.95 IU/ml.
Our data provide evidence for a lack of adequate tetanus immunity in 14.2% of newborns delivered in an Austrian University Hospital. This investigation is emphasizing the importance of stringent regimens concerning prenatal vaccination care, even in countries with generalized immunization programs. If indicated, maternal immunization during pregnancy should be initiated for protection of newborns.
[Show abstract][Hide abstract] ABSTRACT: Following the advent of mefloquine resistance in Plasmodium falciparum in Thailand in the 1990s, the combined treatment of falciparum malaria with artesunate and mefloquine was found to be highly effective in treating and curing the patients in the affected areas. Monitoring of the clinical-parasitological response and of the in vitro sensitivity of P. falciparum was systematically conducted in order to detect any signs of failure of this type of artemisinin-based combination treatment (ACT). In earlier observations the in vitro activity of artemisinin was found to be significantly enhanced when combined with retinol. The same applies to mefloquine. In order to check whether the synergism between artemisinin and mefloquine was maintained in the presence of retinol, the pharmacodynamic interaction of the three compounds was investigated in the western border area of Thailand. Successful parallel tests with mefloquine, artemisinin, retinol, mefloquine-artemisinin 5:1 as well as mefloquine-artemisinin (5:1) + retinol low, medium and high were obtained with 43 fresh parasite isolates. The retinol concentrations in the low, medium and high formulations corresponded to the 50th, 65th and 80th percentile of the physiological mean concentrations in the blood of healthy adults. The IC(50), IC(90) and IC(99) values for mefloquine alone showed a further increase over the data of 2008. In the combinations with artemisinin and retinol moderate synergism was observed at the IC(50), but synergism increased strongly at the IC(90) and the IC(99).
[Show abstract][Hide abstract] ABSTRACT: Estimates of the annual number of infections with Plasmodium vivax reach 391 million. So far the blood-schizontocidal therapy with chloroquine remained effective in most parts of the world, but reports about emerging resistance are increasing. The study had the objective of determining the pharmacodynamic interaction between pyronaridine and retinol in Plasmodium vivax, since pyronaridine is a potential alternative for chloroquine and an earlier study had shown strong synergism between pyronaridine and retinol in Plasmodium falciparum. The study was conducted at the Malaria Clinic of Mae Sot, Tak Province, Thailand, near the border to Myanmar. The in vitro observations followed the method of Tasanor. Successful tests were performed with 44 isolates. The mean IC(50), IC(90) and IC(99) values for pyronaridine were 9.8, 2069.6 and 162446.5 nM. The mean IC(50), IC(90) and IC(99) values for the combinations with retinol (corresponding to the 50th, 65th and 80th percentile of the physiological retinol levels in healthy adults) were 1.7, 542.8 and 59379.5 nM for pyronaridine + retinol "low", for the combination with retinol "medium" they were 0.5, 313.7 and 58891.4 nM and for the combination with retinol "high" they were 0.2, 96.7 and 16754.3 nM. These results suggest strong synergism between the two substances.