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Tumas KC, Xu F, Wu J, Hernandez M, Pattaradilokrat S, Xia L, Peng YC, Lavali AM, He X, Singh BK, Zhang C, Percopo C, Qi CF, Huang S, Long CA, Su XZ. Dysfunction of CD169 + macrophages and blockage of erythrocyte maturation as a mechanism of anemia in Plasmodium yoelii infection. Proc Natl Acad Sci U S A 2023; 120:e2311557120. [PMID: 37748059 PMCID: PMC10556621 DOI: 10.1073/pnas.2311557120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 08/22/2023] [Indexed: 09/27/2023] Open
Abstract
Plasmodium parasites cause malaria with disease outcomes ranging from mild illness to deadly complications such as severe malarial anemia (SMA), pulmonary edema, acute renal failure, and cerebral malaria. In young children, SMA often requires blood transfusion and is a major cause of hospitalization. Malaria parasite infection leads to the destruction of infected and noninfected erythrocytes as well as dyserythropoiesis; however, the mechanism of dyserythropoiesis accompanied by splenomegaly is not completely understood. Using Plasmodium yoelii yoelii 17XNL as a model, we show that both a defect in erythroblastic island (EBI) macrophages in supporting red blood cell (RBC) maturation and the destruction of reticulocytes/RBCs by the parasites contribute to SMA and splenomegaly. After malaria parasite infection, the destruction of both infected and noninfected RBCs stimulates extramedullary erythropoiesis in mice. The continuous decline of RBCs stimulates active erythropoiesis and drives the expansion of EBIs in the spleen, contributing to splenomegaly. Phagocytosis of malaria parasites by macrophages in the bone marrow and spleen may alter their functional properties and abilities to support erythropoiesis, including reduced expression of the adherence molecule CD169 and inability to support erythroblast differentiation, particularly RBC maturation in vitro and in vivo. Therefore, macrophage dysfunction is a key mechanism contributing to SMA. Mitigating and/or alleviating the inhibition of RBC maturation may provide a treatment strategy for SMA.
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Affiliation(s)
- Keyla C. Tumas
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Fangzheng Xu
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Jian Wu
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Maricarmen Hernandez
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Sittiporn Pattaradilokrat
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
- Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok10330, Thailand
| | - Lu Xia
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan410033, China
| | - Yu-chih Peng
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Angela Musu Lavali
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Xiao He
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Brajesh K. Singh
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Cui Zhang
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Caroline Percopo
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Chen-Feng Qi
- Pathology Core, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, NIH, Rockville, MD20852
| | - Suming Huang
- Department of Pediatrics, Division of Pediatric Hematology and Oncology, Penn State Cancer Institute, Hershey, PA17033
- Department of Pharmacology, Division of Pediatric Hematology and Oncology, Penn State Cancer Institute, Hershey, PA17033
| | - Carole A. Long
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
| | - Xin-zhuan Su
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Disease, NIH, Rockville, MD20852
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Salazar-Castañón VH, Juárez-Avelar I, Legorreta-Herrera M, Rodriguez-Sosa M. Macrophage migration inhibitory factor contributes to immunopathogenesis during Plasmodium yoelii 17XL infection. Front Cell Infect Microbiol 2022; 12:968422. [PMID: 36093199 PMCID: PMC9449124 DOI: 10.3389/fcimb.2022.968422] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 08/08/2022] [Indexed: 01/04/2023] Open
Abstract
Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout (Mif -/-) mice were intravenously infected with 1×103 Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Our data showed that Py17XL-infected Wt mice died 11 days postinfection, while Mif -/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif -/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif -/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.
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Affiliation(s)
- Víctor H. Salazar-Castañón
- Laboratorio de Inmunología Molecular, Unidad de Investigación Química Computacional, Síntesis y Farmacología en Moléculas de Interés Biológico, División de Estudios de Posgrado e Investigación, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México (UNAM), Ciudad de México, Mexico
| | - Imelda Juárez-Avelar
- Laboratorio de Inmunidad Innata, Unidad de Investigación en Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Estado de México, Mexico
| | - Martha Legorreta-Herrera
- Laboratorio de Inmunología Molecular, Unidad de Investigación Química Computacional, Síntesis y Farmacología en Moléculas de Interés Biológico, División de Estudios de Posgrado e Investigación, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México (UNAM), Ciudad de México, Mexico,*Correspondence: Miriam Rodriguez-Sosa, ; Martha Legorreta-Herrera,
| | - Miriam Rodriguez-Sosa
- Laboratorio de Inmunidad Innata, Unidad de Investigación en Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Estado de México, Mexico,*Correspondence: Miriam Rodriguez-Sosa, ; Martha Legorreta-Herrera,
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Xie H, Xie S, Wang M, Wei H, Huang H, Xie A, Li J, Fang C, Shi F, Yang Q, Qi Y, Yin Z, Wang X, Huang J. Properties and Roles of γδT Cells in Plasmodium yoelii nigeriensis NSM Infected C57BL/6 Mice. Front Cell Infect Microbiol 2022; 11:788546. [PMID: 35127555 PMCID: PMC8811364 DOI: 10.3389/fcimb.2021.788546] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2021] [Accepted: 12/22/2021] [Indexed: 11/25/2022] Open
Abstract
Background Many kinds of immune cells are involved in malaria infection. γδT cells represent a special type of immune cell between natural and adaptive immune cells that play critical roles in anti-parasite infection. Methods In this study, malaria infection model was constructed. Distribution of γδT cells in various immune organs and dynamic changes of γδT cells in the spleens of C57BL/6 mice after infection were detected by flow cytometry. And activation status of γδT cells was detected by flow cytometry. Then γδT cells in naive and infected mice were sorted and performed single-cell RNA sequencing (scRNA-seq). Finally, γδTCR KO mice model was constructed and the effect of γδT cell depletion on mouse T and B cell immunity against Plasmodium infection was explored. Results Here, splenic γδT cells were found to increase significantly on day 14 after Plasmodium yoelii nigeriensis NSM infection in C57BL/6 mice. Higher level of CD69, ICOS and PD-1, lower level of CD62L, and decreased IFN-γ producing after stimulation by PMA and ionomycin were found in γδT cells from infected mice, compared with naive mice. Moreover, 11 clusters were identified in γδT cells by scRNA-seq based t-SNE analysis. Cluster 4, 5, and 7 in γδT cells from infected mice were found the expression of numerous genes involved in immune response. In the same time, the GO enrichment analysis revealed that the marker genes in the infection group were involved in innate and adaptive immunity, pathway enrichment analysis identified the marker genes in the infected group shared many key signalling molecules with other cells or against pathogen infection. Furthermore, increased parasitaemia, decreased numbers of RBC and PLT, and increased numbers of WBC were found in the peripheral blood from γδTCR KO mice. Finally, lower IFN-γ and CD69 expressing CD4+ and CD8+ T cells, lower B cell percentage and numbers, and less CD69 expressing B cells were found in the spleen from γδTCR KO infected mice, and lower levels of IgG and IgM antibodies in the serum were also observed than WT mice. Conclusions Overall, this study demonstrates the diversity of γδT cells in the spleen of Plasmodium yoelii nigeriensis NSM infected C57BL/6 mice at both the protein and RNA levels, and suggests that the expansion of γδT cells in cluster 4, 5 and 7 could promote both cellular and humoral immune responses.
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Affiliation(s)
- Hongyan Xie
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Shihao Xie
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Mei Wang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Haixia Wei
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - He Huang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Anqi Xie
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Jiajie Li
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Chao Fang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Feihu Shi
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Quan Yang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Yanwei Qi
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Zhinan Yin
- Zhuhai Precision Medical Center, Zhuhai People’s Hospital (Zhuhai Hospital Affiliated with Jinan University), Jinan University, Zhuhai, China
- The Biomedical Translational Research Institute, Faculty of Medical Science, Jinan University, Guangzhou, China
| | - Xinhua Wang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- *Correspondence: Xinhua Wang, ; Jun Huang,
| | - Jun Huang
- State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Immunology, Sino-French Hoffmann Institute, Guangzhou Medical University, Guangzhou, China
- *Correspondence: Xinhua Wang, ; Jun Huang,
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Wang H, Li S, Cui Z, Qin T, Shi H, Ma J, Li L, Yu G, Jiang T, Li C. Analysis of spleen histopathology, splenocyte composition and haematological parameters in four strains of mice infected with Plasmodium berghei K173. Malar J 2021; 20:249. [PMID: 34090420 PMCID: PMC8180108 DOI: 10.1186/s12936-021-03786-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 05/27/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Malaria is a fatal disease that presents clinically as a continuum of symptoms and severity, which are determined by complex host-parasite interactions. Clearance of infection is believed to be accomplished by the spleen and mononuclear phagocytic system (MPS), independent of artemisinin treatment. The spleen filters infected red blood cells (RBCs) from circulation through immune-mediated recognition of the infected RBCs followed by phagocytosis. This study evaluated the tolerance of four different strains of mice to Plasmodium berghei strain K173 (P. berghei K173), and the differences in the role of the spleen in controlling P. berghei K173 infection. METHODS Using different strains of mice (C57BL/6, BALB/C, ICR, and KM mice) infected with P. berghei K173, the mechanisms leading to splenomegaly, histopathology, splenocyte activation and proliferation, and their relationship to the control of parasitaemia and host mortality were examined and evaluated. RESULTS Survival time of mice infected with P. berghei K173 varied, although the infection was uniformly lethal. Mice of the C57BL/6 strain were the most resistant, while mice of the strain ICR were the most susceptible. BALB/c and KM mice were intermediate. In the course of P. berghei K173 infection, all infected mice experienced significant splenomegaly. Parasites were observed in the red pulp at 3 days post infection (dpi) in all animals. All spleens retained late trophozoite stages as well as a fraction of earlier ring-stage parasites. The percentages of macrophages in infected C57BL/6 and KM mice were higher than uninfected mice on 8 dpi. Spleens of infected ICR and KM mice exhibited structural disorganization and remodelling. Furthermore, parasitaemia was significantly higher in KM versus C57BL/6 mice at 8 dpi. The percentages of macrophages in ICR infected mice were lower than uninfected mice, and the parasitaemia was higher than other strains. CONCLUSIONS The results presented here demonstrate the rate of splenic mechanical filtration and that splenic macrophages are the predominant roles in controlling an individual's total parasite burden. This can influence the pathogenesis of malaria. Finally, different genetic backgrounds of mice have different splenic mechanisms for controlling malaria infection.
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Affiliation(s)
- Huajing Wang
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
- Artemisinin Research Center, China Academy of Traditional Chinese Medical Sciences, Beijing, China
| | - Shuo Li
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
- Artemisinin Research Center, China Academy of Traditional Chinese Medical Sciences, Beijing, China
| | - Zhao Cui
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
| | - Tingting Qin
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
- Artemisinin Research Center, China Academy of Traditional Chinese Medical Sciences, Beijing, China
| | - Hang Shi
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
| | - Ji Ma
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
- Artemisinin Research Center, China Academy of Traditional Chinese Medical Sciences, Beijing, China
| | - Lanfang Li
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
| | - Guihua Yu
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
| | - Tingliang Jiang
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China
- Artemisinin Research Center, China Academy of Traditional Chinese Medical Sciences, Beijing, China
| | - Canghai Li
- Tang Center for Herbal Medicine Research, Institute of Chinese Materia Medica, China Academy of Traditional Chinese Medical Sciences, No. 16 Dongzhimen Nanxiaojie, Dongcheng District, Beijing, 100700, China.
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Salazar-Castañón VH, Juárez-Avelar I, Legorreta-Herrera M, Govezensky T, Rodriguez-Sosa M. Co-infection: the outcome of Plasmodium infection differs according to the time of pre-existing helminth infection. Parasitol Res 2018; 117:2767-2784. [PMID: 29938323 DOI: 10.1007/s00436-018-5965-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 06/07/2018] [Indexed: 01/28/2023]
Abstract
Although helminth-Plasmodium coinfections are common in tropical regions, the implications of this co-existence for the host immune response are poorly understood. In order to understand the effect of helminth infection at different times of coinfection on the immune response against Plasmodium infection, BALB/c mice were intraperitoneally infected with Taenia crassiceps (Tc). At 2 (Tc2) or 8 (Tc8) weeks post-infection, mice were intravenously infected with 1 × 103 Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Py 17XL-single-infected mice developed cachexia, splenomegaly, and anemia, and died at 11 days post-infection. Importantly, Tc2 + Py-coinfected mice showed increased survival of 58% on day 11, but developed pathology (cachexia and splenomegaly) and succumbed on day 18 post-coinfection, this latter associated with high levels of IL-1β and IL-12, and reduced IFN-γ in serum compared with Py 17XL-single-infected mice. Interestingly, Tc8 + Py-coinfected mice showed increased survival up to 80% on day 11 and succumbed on day 30 post-coinfection. This increased survival rate conferred by chronic helminth infection was associated with a decreased pathology and mixed inflammatory-type 1/anti-inflammatory-type 2 immune profile as evidenced by the production of high levels of IL-12 and IL-10, and reduced TNF-α from macrophages, high levels of IL-4 and IL-10, and low levels of IFN-γ from spleen cells. Also high serum levels of IL-1β, TNF-α, IL-12, IL-4, and IL-10, but a significant reduction of IFN-γ were observed. Together, these data indicate that polarization of the cell-mediated response modulated by a pre-existing helminth infection differentially impacts on the host immune response to Py 17XL in a time-dependent manner.
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Affiliation(s)
- Víctor H Salazar-Castañón
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México (UNAM), Avenida de los Barrios Número 1, Colonia Los Reyes Iztacala, C.P. 54090, Tlalnepantla, Estado de México, Mexico
| | - Imelda Juárez-Avelar
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México (UNAM), Avenida de los Barrios Número 1, Colonia Los Reyes Iztacala, C.P. 54090, Tlalnepantla, Estado de México, Mexico
| | - Martha Legorreta-Herrera
- Laboratorio de Inmunología Molecular, Facultad de Estudios Superiores Zaragoza, Universidad Nacional Autónoma de México (UNAM), Batalla 5 de mayo s/n, Col. Ejército de Oriente, Iztapalapa, C.P. 09230, Ciudad de México, Mexico
| | - Tzipe Govezensky
- Departamento de Biología Molecular, Instituto de Investigaciones Biomédicas, Universidad Nacional Autònoma de México (UNAM), Ciudad de México, Mexico
| | - Miriam Rodriguez-Sosa
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México (UNAM), Avenida de los Barrios Número 1, Colonia Los Reyes Iztacala, C.P. 54090, Tlalnepantla, Estado de México, Mexico.
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Antibody-independent mechanisms regulate the establishment of chronic Plasmodium infection. Nat Microbiol 2017; 2:16276. [PMID: 28165471 DOI: 10.1038/nmicrobiol.2016.276] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 12/22/2016] [Indexed: 01/15/2023]
Abstract
Malaria is caused by parasites of the genus Plasmodium. All human-infecting Plasmodium species can establish long-lasting chronic infections1-5, creating an infectious reservoir to sustain transmission1,6. It is widely accepted that the maintenance of chronic infection involves evasion of adaptive immunity by antigenic variation7. However, genes involved in this process have been identified in only two of five human-infecting species: Plasmodium falciparum and Plasmodium knowlesi. Furthermore, little is understood about the early events in the establishment of chronic infection in these species. Using a rodent model we demonstrate that from the infecting population, only a minority of parasites, expressing one of several clusters of virulence-associated pir genes, establishes a chronic infection. This process occurs in different species of parasites and in different hosts. Establishment of chronicity is independent of adaptive immunity and therefore different from the mechanism proposed for maintenance of chronic P. falciparum infections7-9. Furthermore, we show that the proportions of parasites expressing different types of pir genes regulate the time taken to establish a chronic infection. Because pir genes are common to most, if not all, species of Plasmodium10, this process may be a common way of regulating the establishment of chronic infections.
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