Evaluating seroprevalence to circumsporozoite protein to estimate exposure to three species of Plasmodium in the Brazilian Amazon.

BACKGROUND: Brazil has seen a great decline in malaria and the country is moving towards elimination. However, for eventual elimination, the control program needs efficient tools in order to monitor malaria exposure and transmission. In this study, we aimed to evaluate whether seroprevalence to the circumsporozoite protein (CSP) is a good tool for monitoring the exposure to and/or evaluating the burden and distribution of Plasmodium species in the Brazilian Amazon. METHODS: Cross-sectional surveys were conducted in a rural area of Porto Velho, Rondônia state. Parasite infection was detected by microscopy and polymerase chain reaction. Antibodies to the sporozoite CSP repeats of Plasmodium vivax, P. falciparum, and P. malariae (PvCS, PfCS, and PmCS) were detected using the enzyme-linked immunosorbent assay technique. Human leukocyte antigen (HLA)-DRB1 and DQB1 genes were typed using Luminex® xMAP® technology. RESULTS: The prevalence of immunoglobulin G against P. vivax CSP peptide (62%) was higher than P. falciparum (49%) and P. malariae (46%) CSP peptide. Most of the studied individuals had antibodies to at least one of the three peptides (72%), 34% had antibodies to all three peptides and 28% were non-responders. Although the majority of the population was not infected at the time of the survey, 74.3% of parasite-negative individuals had antibodies to at least one of the CSPs. Importantly, among individuals carrying the haplotypes DRB1*04~DQB1*03, there was a significantly higher frequency of PfCS responders, and DRB1*16~DQB1*03 haplotype for PvCS and PfCS responders. In contrast, HLA-DRB1*01 and HLA-DQB1*05 allelic groups were associated with a lack of antibodies to P. vivax and P. falciparum CSP repeats, and the haplotype DRB1*01~DQB1*05 was also associated with non-responders, including non-responders to P. malariae. CONCLUSIONS: Our results show that in low transmission settings, naturally acquired antibody responses against the CSP repeats of P. vivax, P. falciparum, and P. malariae in a single cross-sectional study may not represent a valuable marker for monitoring recent malaria exposure, especially in an area with a high prevalence of P. vivax. Furthermore, HLA class II molecules play an important role in antibody response and require further study with a larger sample size. It will be of interest to consider HLA analysis when using serosurveillance to monitor malaria exposure among genetically diverse populations.

Evaluating seroprevalence to circumsporozoite protein to estimate exposure to three species of Plasmodium in the Brazilian Amazon

BACKGROUND: Brazil has seen a great decline in malaria and the country is moving towards elimination. However, for eventual elimination, the control program needs efficient tools in order to monitor malaria exposure and transmission. In this study, we aimed to evaluate whether seroprevalence to the circumsporozoite protein (CSP) is a good tool for monitoring the exposure to and/or evaluating the burden and distribution of Plasmodium species in the Brazilian Amazon. METHODS: Cross-sectional surveys were conducted in a rural area of Porto Velho, Rondônia state. Parasite infection was detected by microscopy and polymerase chain reaction. Antibodies to the sporozoite CSP repeats of Plasmodium vivax, P. falciparum, and P. malariae (PvCS, PfCS, and PmCS) were detected using the enzyme-linked immunosorbent assay technique. Human leukocyte antigen (HLA)-DRB1 and DQB1 genes were typed using Luminex® xMAP® technology. RESULTS: The prevalence of immunoglobulin G against P. vivax CSP peptide (62%) was higher than P. falciparum (49%) and P. malariae (46%) CSP peptide. Most of the studied individuals had antibodies to at least one of the three peptides (72%), 34% had antibodies to all three peptides and 28% were non-responders. Although the majority of the population was not infected at the time of the survey, 74.3% of parasite-negative individuals had antibodies to at least one of the CSPs. Importantly, among individuals carrying the haplotypes DRB1*04~DQB1*03, there was a significantly higher frequency of PfCS responders, and DRB1*16~DQB1*03 haplotype for PvCS and PfCS responders. In contrast, HLA-DRB1*01 and HLA-DQB1*05 allelic groups were associated with a lack of antibodies to P. vivax and P. falciparum CSP repeats, and the haplotype DRB1*01~DQB1*05 was also associated with non-responders, including non-responders to P. malariae. CONCLUSIONS: Our results show that in low transmission settings, naturally acquired antibody responses against the CSP repeats of P. vivax, P. falciparum, and P. malariae in a single cross-sectional study may not represent a valuable marker for monitoring recent malaria exposure, especially in an area with a high prevalence of P. vivax. Furthermore, HLA class II molecules play an important role in antibody response and require further study with a larger sample size. It will be of interest to consider HLA analysis when using serosurveillance to monitor malaria exposure among genetically diverse populations

Avaliação da resposta imune humoral contra proteínas de superfície de merozoítas (MSP1-19, AMA-1 e RBP-123-751) de Plasmodium vivax e sua associação com HLA de classe II em indivíduos residentes em áreas endêmicas / Evaluation of the humoral immune response against merozoite surface proteins (msp1-19, ama-1 e rbp-123-751) of plasmodium vivax and its association with class ii hla in individuals living in endemic areas

Embora complexa e multifatorial, a aquisição da imunidade clínica à malária é dependente da resposta mediada por anticorpos. No entanto, variações na resposta de anticorpos determinadas por características epidemiológicas ou polimorfismos genéticos dos genes HLA de classe II podem influenciar diretamente esse processo. Nesse sentido, estudos com foco na influência dos alelos de classe II na resposta imune em populações naturalmente expostas são extremamente necessários no desenvolvimento de vacinas contra o Plasmodium vivax. Portanto, neste estudo nós avaliamos as possíveis associações entre os grupos alélicos HLA-DRB1* e HLA-DQB1* detectados por PCR-SSO (Luminex) e resposta humoral mediada por anticorpos IgG e subclasses (ELISA) contra três proteínas recombinantes:PvMSP1 19, PvRBP123-751 e PvAMA-1 em 565 indivíduos da Amazônia brasileira. Nossos resultados demonstram que as proteínas PvMSP1 19, PvRBP123-751 e PvAMA-1 foram altamente imunogênicas sendo reconhecidas respectivamente por 75,8 por cento, 73,5 por cento e 60,7 por cento da população estudada e as subclasses de anticorpos citofílicos IgG1 e/ou IgG3 foram predominantes na resposta contra todas as proteínas. Em relação aos dados epidemiológicos observamos que os níveis de IgG contra as três proteínas foram associados com o número de infecções maláricas anteriores e com o tempo de exposição em área endêmica, relacionando a estas proteínas um efeito cumulativo na resposta humoral. No entanto, este efeito parece ser dependente de infecções constantes uma vez que o tempo desde a última malária teve correlação inversa e significativa com o índice de reatividade de anticorpos IgG anti-MSP1 19, anti-AMA-1 e anti-RBP-123-751...

Although complex and multifactorial,the acquisition of clinical immunity to malaria is dependent of antibody-mediated immuneresponse. However, variations in antibody response could be determined by epidemiologicalcharacteristics or genetic polymorphisms in HLA class II genes. In this scenario, studiesaiming the evaluation of HLA class II alleles and its influence in the specific immuneresponse of naturally exposed populations are necessary in the development of vaccinesagainst P. vivax. Therefore, we evaluated the possible association between allelic groupsHLA-DRB1* and HLA-DQB1* detected by PCR-SSO (Luminex) and humoral responsemediated by IgG and subclass (ELISA) against three recombinant proteins: PvMSP1-19,PvRBP123-751 and PvAMA-1 in 565 individuals in the Brazilian Amazon. Our resultsdemonstrate that PvMSP1-19, PvRBP123-751 and PvAMA-1 were highly immunogenic andrecognized by respectively 75.8 percent, 73.5 percent and 60.7 percent of studied population and subclasses ofcytophilic antibodies IgG1 and/or IgG3 were predominant in response against all proteins.Concerning the epidemiological data we observed that IgG levels against the three proteinswere associated with the number of previous malaria infections and time of exposure inendemic area, relating to these proteins a cumulative effect on the humoral response.However, this effect appears to be dependent of constant infections since the time since thelast malaria has an inverse correlation with the IR of anti-MSP1 19 IgG antibodies, anti-AMA-1 and anti-RBP-123- 751. Lastly, we evaluated the frequency of IgG antibody response byallelic groups of HLA class II...

Evaluation of naturally acquired IgG antibodies to a chimeric and non-chimeric recombinant species of Plasmodium vivax reticulocyte binding protein-1: lack of association with HLA-DRB1*/DQB1* in malaria exposed individuals from the Brazilian Amazon.

The development of modular constructs that include antigenic regions targeted by protective immune responses is an attractive approach for subunit vaccine development. However, a main concern of using these vaccine platforms is how to preserve the antigenic identity of conformational B cell epitopes. In the present study we evaluated naturally acquired antibody responses to a chimeric protein engineered to contain a previously defined immunodominant domain of the Plasmodium vivax reticulocyte binding protein-1 located between amino acid positions K435-I777. The construct also includes three regions of the cognate protein (F571-D587, I1745-S1786 and L2235-E2263) predicted to contain MHC class II promiscuous T cell epitopes. Plasma samples from 253 naturally exposed individuals were tested against this chimeric protein named PvRMC-RBP1 and a control protein that includes the native sequence PvRBP123-751 in comparative experiments to study the frequency of total IgG and IgG subclass reactivity. HLA-DRB1 and HLA-DQB1 allelic groups were typed by PCR-SSO to evaluate the association between major HLA class II alleles and antibody responses. We found IgG antibodies that recognized the chimeric PvRMC-RBP1 and the PvRBP123-751 in 47.1% and 60% of the studied population, respectively. Moreover, the reactivity index against both proteins were comparable and associated with time of exposure (p<0.0001) and number of previous malaria episodes (p<0.005). IgG subclass profile showed a predominance of cytophilic IgG1 over other subclasses against both proteins tested. Collectively these studies suggest that the chimeric PvRMC-RBP1 protein retained antigenic determinants in the PvRBP1435-777 native sequence. Although 52.9% of the population did not present detectable titers of antibodies to PvRMC-RBP1, genetic restriction to this chimeric protein does not seem to occur, since no association was observed between the HLA-DRB1* or HLA-DQB1* alleles and the antibody responses. This experimental evidence strongly suggests that the identity of the conformational B cell epitopes is preserved in the chimeric protein.