RESUMEN
Severe malarial anemia (SMA) is the most frequent life-threatening complication of malaria and may contribute to the majority of malarial deaths worldwide. To explore the mechanisms of pathogenesis, we developed a novel murine model of SMA in which parasitemias peaked around 1.0% of circulating red blood cells (RBCs) and yet hemoglobin levels fell to 47% to 56% of baseline. The severity of anemia was independent of the level of peak or cumulative parasitemia, but was linked kinetically to the duration of patent infection. In vivo biotinylation analysis of the circulating blood compartment revealed that anemia arose from accelerated RBC turnover. Labeled RBCs were reduced to 1% of circulating cells by 8 days after labeling, indicating that the entire blood compartment had been turned over in approximately one week. The survival rate of freshly transfused RBCs was also markedly reduced in SMA animals, but was not altered when RBCs from SMA donors were transferred into naive recipients, suggesting few functional modifications to target RBCs. Anemia was significantly alleviated by depletion of either phagocytic cells or CD4+ T lymphocytes. This study demonstrates that immunologic mechanisms may contribute to SMA by promoting the accelerated turnover of uninfected RBCs.
Asunto(s)
Anemia/inmunología , Linfocitos T CD4-Positivos/inmunología , Eritrocitos/inmunología , Malaria/inmunología , Plasmodium berghei/inmunología , Anemia/complicaciones , Anemia/patología , Animales , Linfocitos T CD4-Positivos/patología , Modelos Animales de Enfermedad , Eritrocitos/parasitología , Eritrocitos/patología , Malaria/complicaciones , Malaria/patología , Ratones , Ratones Endogámicos BALB C , Ratas , Ratas WistarRESUMEN
The natural killer complex (NKC) is a genetic region of highly linked genes encoding several receptors involved in the control of NK cell function. The NKC is highly polymorphic, and allelic variability of various NKC loci has been demonstrated in inbred mice. Making use of BALB.B6-Cmv1r congenic mice, in which the NKC from disease-susceptible C57BL/6 mice has been introduced into the disease-resistant BALB/c background, we show here that during murine malaria infection, the NKC regulates a range of pathophysiological syndromes such as cerebral malaria, pulmonary edema, and severe anemia, which contribute to morbidity and mortality in human malaria. Parasitemia levels were not affected by the NKC genotype, indicating that control of malarial fatalities by the NKC cells does not operate through effects on parasite growth rate. Parasite-specific antibody responses and the proinflammatory gene transcription profile, as well as the TH1/TH2 balance, also appeared to be influenced by NKC genotype, providing evidence that this region, known to control innate immune responses via NK and/or NK T-cell activation, can also significantly regulate acquired immunity to infection. To date, NKC-encoded innate system receptors have been shown mainly to regulate viral infections. Our data provide evidence for critical NKC involvement in the broad immunological responses to a protozoan parasite.
Asunto(s)
Células Asesinas Naturales/inmunología , Malaria/inmunología , Plasmodium berghei/inmunología , Anemia/etiología , Animales , Anticuerpos Antiprotozoarios/sangre , Encéfalo/patología , Perfilación de la Expresión Génica , Interferón gamma/biosíntesis , Malaria/patología , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Edema Pulmonar/etiología , Factor de Crecimiento Transformador beta/biosíntesisRESUMEN
The primary pathophysiological events contributing to fatal malaria are the cerebral syndrome, anemia, and lactic acidosis. The molecular basis of each event has been unclear. In the present study, microarray analysis of murine transcriptional responses during the development of severe disease revealed temporal, organ-specific, and pathway-specific patterns. More than 400 genes in the brain and 600 genes in the spleen displayed transcriptional changes. Dominant patterns revealed strongly suppressed erythropoiesis, starting early during infection, and highly up-regulated transcription of genes that control host glycolysis, including lactate dehydrogenase. The latter presents a mechanism that may contribute to metabolic acidosis. No evidence for hypoxia-mediated regulation of these events was observed. Interferon-regulated gene transcripts dominated the inflammatory response to cytokines. These results demonstrate previously unknown transcriptional changes in the host that may underlie the development of malarial syndromes, such as anemia and metabolic dysregulation, and increase the utility of murine models in investigation of basic malarial pathogenesis.
Asunto(s)
Eritropoyesis/genética , Glucólisis/genética , Interferón gamma/genética , Malaria/genética , Malaria/metabolismo , Plasmodium berghei , Transcripción Genética/genética , Animales , ADN/genética , Perfilación de la Expresión Génica , Interferón gamma/biosíntesis , Malaria/sangre , Malaria/patología , Ratones , Ratones Endogámicos BALB C , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Transcripción Genética/fisiología , Regulación hacia Arriba/fisiologíaRESUMEN
Inbred strains of mice infected with Leishmania major have been classified as genetically resistant or susceptible on the basis of their ability to cure their lesions, the parasite burden in the draining lymph nodes, and their type of T helper cell immune responses to the parasite. Using the intradermal infection at the base of the tail and the ear pinna, we compared for the first time the above-mentioned parameters in six strains of mice infected with metacyclic promastigotes, and we show that the severity of disease depends greatly on the site of infection. Although the well-documented pattern of disease susceptibility of BALB/c and C57BL/6 mice described for the footpad and base-of-the-tail models of leishmaniasis were confirmed, C3H/HeN and DBA/2 mice, which are intermediate and susceptible, respectively, in the tail and other models, were resistant to ear infection. Moreover, in the CBA/H, C3H/HeN, C57BL/6J, and DBA/2 mouse strains, there was little correlation between the pattern of cytokines produced and the disease phenotype observed at the ear and tail sites. We conclude that the definition of susceptibility and the immune mechanisms leading to susceptibility or resistance to infection may differ substantially depending on the route of infection.
Asunto(s)
Oído/parasitología , Leishmania major/patogenicidad , Leishmaniasis Cutánea/inmunología , Índice de Severidad de la Enfermedad , Cola (estructura animal)/parasitología , Animales , Femenino , Inyecciones Intradérmicas , Leishmania major/inmunología , Leishmaniasis Cutánea/parasitología , Leishmaniasis Cutánea/fisiopatología , Ratones , Ratones EndogámicosRESUMEN
CD1d-restricted NKT cells are a novel T cell lineage with unusual features. They co-express some NK cell receptors and recognize glycolipid antigens through an invariant T cell receptor (TCR) in the context of CD1d molecules. Upon activation through the TCR, NKT cells produce large amounts of IFN-gamma and IL-4. It has been proposed that rapid cytokine output by activated NKT cells may induce bystander activation of other lymphoid lineages. The impact of CD1d-restricted NKT cell activation in the induction of B cell-mediated immune responses to infection is still unclear. We show here that CD1-restricted NKT cells contribute to malarial splenomegaly associated with expansion of the splenic B cell pool and enhance parasite-specific antibody formation in response to Plasmodium berghei infection. The increased B cell-mediated response correlates with the ability of NKT cells to promote Th2 immune responses. Additionally, antibody responses against the glycosylphosphatidylinositol (GPI)-anchored protein merozoite surface protein 1 (MSP-1) were found to be significantly lower in CD1(-/-) mice compared to wild-type animals. P. berghei-infected MHC class II (MHCII)(-/-) mice also generated antibodies against MSP-1, suggesting that antibody production against GPI-anchored antigens in response to malaria infection can arise from both MHCII-dependent and independent pathways.
Asunto(s)
Antígenos CD1/metabolismo , Células Asesinas Naturales/metabolismo , Malaria/metabolismo , Esplenomegalia/metabolismo , Animales , Anticuerpos Antiprotozoarios/inmunología , Anticuerpos Antiprotozoarios/metabolismo , Antígenos CD1/genética , Antígenos CD1/inmunología , Antígenos CD1d , Linfocitos B/metabolismo , Antígenos de Histocompatibilidad Clase II/genética , Inmunoglobulina G/biosíntesis , Inmunoglobulina M/biosíntesis , Células Asesinas Naturales/inmunología , Malaria/inmunología , Ratones , Plasmodium berghei/inmunología , Plasmodium berghei/metabolismo , Esplenomegalia/inmunologíaRESUMEN
NKT cells are specialized cells coexpressing NK and T cell receptors. Upon activation they rapidly produce high levels of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) and are therefore postulated to influence T(H)1/T(H)2 immune responses. The precise role of the CD1/NKT cell pathway in immune response to infection remains unclear. We show here that CD1d-restricted NKT cells from distinct genetic backgrounds differentially influence T(H)1/T(H)2 polarization, proinflammatory cytokine levels, pathogenesis, and fatality in the P. berghei ANKA/rodent model of cerebral malaria. The functional properties of CD1d-restricted NKT cells vary according to expression of loci of the natural killer complex (NKC) located on mouse chromosome 6, which is shown here to be a significant genetic determinant of murine malarial fatalities.
Asunto(s)
Antígenos CD1/metabolismo , Células Asesinas Naturales/inmunología , Malaria Cerebral/inmunología , Subgrupos de Linfocitos T/inmunología , Animales , Antígenos/metabolismo , Antígenos CD1/genética , Antígenos CD1d , Antígenos de Superficie , Citocinas/biosíntesis , Lectinas Tipo C , Malaria Cerebral/etiología , Malaria Cerebral/genética , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Noqueados , Subfamilia B de Receptores Similares a Lectina de Células NK , Plasmodium berghei , Proteínas/metabolismo , Receptores de Antígenos de Linfocitos T alfa-beta/metabolismo , Células TH1/inmunología , Células Th2/inmunologíaRESUMEN
A major advance has been made towards the positional cloning of char2 (a quantitative trait locus encoding resistance to Plasmodium chabaudi malaria). Mice congenic for the locus have been used to fine map the gene and to prove that char2 plays a significant role in the outcome of malarial infection, independently of other resistance loci.