RESUMEN
Leptospirosis is a zoonotic spirochetal disease of global importance. This disease continues to have a major impact on people living in urban and rural areas of developing countries with inestimable morbidity and mortality. Funding for research and control efforts is currently haphazard, not organized and not effective for public health efforts, primarily because there are no concerted, ongoing international efforts to assess the impact of leptospirosis on human health. Major issues in the field need to be addressed to develop strategies of control, amelioration and treatment. These include the following: mechanisms of naturally acquired and vaccine-induced protective immunity against clinical leptospirosis; mechanisms of severe leptospirosis pathogenesis; standardized, precise and simplified taxonomy of Leptospira relevant to disease manifestations, transmission and control; effective adjunct treatments in addition to antimicrobials; and environmental assessment for risk of leptospirosis transmission and relevant mammalian reservoirs. Once effective ongoing, collaborative international efforts to assess the impact of leptospirosis on human and veterinary health are underway, appropriate mobilization of clinical and public health research funding will follow.
Asunto(s)
Leptospirosis , Humanos , Leptospirosis/diagnóstico , Leptospirosis/etiología , Leptospirosis/terapia , Factores de RiesgoRESUMEN
The Plasmodium ookinete is the developmental stage of the malaria parasite that invades the mosquito midgut. The ookinete faces two physical barriers in the midgut which it must traverse to become an oocyst: the chitin- and protein-containing peritrophic matrix; and the midgut epithelial cell. This chapter will consider basic aspects of ookinete biology, molecules known to be involved in midgut invasion, and cellular processes of the ookinete that facilitate parasite invasion. Detailed knowledge of these mechanisms may be exploitable in the future towards developing novel strategies of blocking malaria transmission.
Asunto(s)
Culicidae/parasitología , Plasmodium/fisiología , Animales , Anticuerpos Antiprotozoarios/inmunología , Sistema Digestivo/parasitología , Plasmodium/crecimiento & desarrollo , Plasmodium/inmunologíaRESUMEN
Malaria transmission-blocking strategies aimed at disrupting parasite-mosquito interactions have the potential to make important contributions to global malaria control. It has been suggested that Plasmodium-secreted chitinase plays a crucial role in allowing the ookinete to initiate its invasion of the mosquito midgut, which suggests that this enzyme is a candidate target for blocking malaria transmission. In this review, the authors discuss Plasmodium chitinases from the molecular, biochemical and cell biology viewpoints. Future directions of study could involve developing strategies for interrupting the function of Plasmodium chitinases within the mosquito midgut, including transmission-blocking drugs or vaccines, or the development of chitinase-inhibitor-producing transgenic mosquitoes.
Asunto(s)
Quitinasas/metabolismo , Culicidae/parasitología , Plasmodium/enzimología , Animales , Animales Modificados Genéticamente , Interacciones Huésped-Parásitos , Modelos MolecularesRESUMEN
To initiate invasion of the mosquito midgut, Plasmodium ookinetes secrete chitinolytic activity to penetrate the peritrophic matrix surrounding the blood meal. While ookinetes of the avian malaria parasite Plasmodium gallinaceum appear to secrete products of two chitinase genes, to date only one chitinase gene, PfCHT1, has been identified in the nearly completed Plasmodium falciparum strain 3D7 genome database. To test the hypothesis that the single identified chitinase of P. falciparum is necessary for ookinete invasion, the PfCHT1 gene was disrupted 39 bp upstream of the stop codon. PfCHT1-disrupted parasites had normal gametocytogenesis, exflagellation, and ookinete formation but were markedly impaired in their ability to form oocysts in Anopheles freeborni midguts. Confocal microscopy demonstrated that the truncated PfCHT1 protein was present in mutant ookinetes but that the concentration of mutant PfCHT1 within the apical end of the ookinetes was substantially reduced. These data suggest that full-length PfCHT1 is essential for intracellular trafficking and secretion and that the PfCHT1 gene product is necessary for ookinetes to invade the mosquito midgut.
Asunto(s)
Anopheles/parasitología , Eliminación de Gen , Plasmodium falciparum/enzimología , Plasmodium falciparum/patogenicidad , Estómago/parasitología , Animales , Humanos , Malaria Falciparum/parasitología , Microscopía Confocal , Plásmidos , Plasmodium falciparum/genética , Plasmodium falciparum/crecimiento & desarrollo , Reacción en Cadena de la Polimerasa , VirulenciaRESUMEN
During mosquito transmission, malaria ookinetes must cross a chitin-containing structure known as the peritrophic matrix (PM), which surrounds the infected blood meal in the mosquito midgut. In turn, ookinetes produce multiple chitinase activities presumably aimed at disrupting this physical barrier to allow ookinete invasion of the midgut epithelium. Plasmodium chitinase activities are demonstrated targets for human and avian malaria transmission blockade with the chitinase inhibitor allosamidin. Here, we identify and characterize the first chitinase gene of a rodent malaria parasite, Plasmodium berghei. We show that the gene, named PbCHT1, is a structural ortholog of PgCHT1 of the avian malaria parasite Plasmodium gallinaceum and a paralog of PfCHT1 of the human malaria parasite Plasmodium falciparum. Targeted disruption of PbCHT1 reduced parasite infectivity in Anopheles stephensi mosquitoes by up to 90%. Reductions in infectivity were also observed in ookinete feeds-an artificial situation where midgut invasion occurs before PM formation-suggesting that PbCHT1 plays a role other than PM disruption. PbCHT1 null mutants had no residual ookinete-derived chitinase activity in vitro, suggesting that P. berghei ookinetes express only one chitinase gene. Moreover, PbCHT1 activity appeared insensitive to allosamidin inhibition, an observation that raises questions about the use of allosamidin and components like it as potential malaria transmission-blocking drugs. Taken together, these findings suggest a fundamental divergence among rodent, avian, and human malaria parasite chitinases, with implications for the evolution of Plasmodium-mosquito interactions.
Asunto(s)
Anopheles/parasitología , Quitinasas/genética , Eliminación de Gen , Plasmodium berghei/enzimología , Plasmodium berghei/patogenicidad , Secuencia de Aminoácidos , Animales , Animales Modificados Genéticamente , Quitinasas/metabolismo , Interacciones Huésped-Parásitos , Malaria/parasitología , Datos de Secuencia Molecular , Plasmodium berghei/genética , Plasmodium berghei/crecimiento & desarrollo , Análisis de Secuencia de ADNRESUMEN
In malaria due to Plasmodium falciparum, life-threatening complications are in part related to the degree of parasitemia. Whole blood exchange and red blood cell exchange (RCE) have been used for the rapid removal of parasites from the circulation of patients with a high parasite load complicated by cerebral, pulmonary, and renal dysfunction. We have treated three 5-45-year-old patients with hyperparasitemia and end-organ dysfunction with red cell exchange by automated apheresis as an adjunct to specific anti-malarial chemotherapy. Parasitemia dropped more than 80% in all three patients immediately after the exchange, and all patients had an uneventful and full recovery. In combination with effective anti-malarial chemotherapy, apheresis RCE is a safe and rapid approach to treat complicated malaria due to P. falciparum.
Asunto(s)
Citaféresis , Transfusión de Eritrocitos , Malaria Falciparum/terapia , Adulto , Animales , Preescolar , Femenino , Humanos , Malaria Cerebral/etiología , Malaria Cerebral/terapia , Malaria Falciparum/complicaciones , Masculino , Persona de Mediana Edad , Parasitemia/terapia , Plasmodium falciparumRESUMEN
Leishmania parasites produce chitinase activity (EC. 3.2.1.14) thought to be important in parasite-sandfly interactions and transmission of the parasite to the vertebrate host. Previous observations have suggested that parasite chitinases are involved in degradation of the sandfly peritrophic matrix and the chitinous layer of the cardiac valve cuticle. This chitinase activity is thought to produce an incompetent pharyngeal valve sphincter and a route of egress that allow Leishmania promastigotes to be regurgitated into the site of blood feeding. In the studies reported here, enzymatically active L. donovani chitinase LdCHT1 was expressed as a thioredoxin fusion protein in Escherichia coli strain AD494 (DE3). Recombinant LdCHT1 had a predominantly endochitinase activity, in contrast to previous reports of both exo- and endochitinase activities in axenic culture supernatants of diverse Leishmania spp. promastigotes. The predominant endochitinase activity of recombinant LdCHT1 is consistent with the presumed function of the enzyme in disrupting chitinous structures in the sandfly digestive system to allow transmission.
Asunto(s)
Acetilglucosamina/análogos & derivados , Quitinasas/genética , Regulación Enzimológica de la Expresión Génica , Himecromona/análogos & derivados , Leishmania donovani/enzimología , Acetilglucosamina/metabolismo , Animales , Quitina/metabolismo , Quitinasas/aislamiento & purificación , Quitinasas/metabolismo , Cromatografía en Gel , Cromatografía en Capa Delgada , Escherichia coli/enzimología , Escherichia coli/genética , Fluorometría , Concentración de Iones de Hidrógeno , Hidrólisis , Himecromona/metabolismo , Leishmania donovani/genética , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Especificidad por SustratoRESUMEN
Leptospirosis is a globally important zoonotic disease that affects humans on all continents, in both urban and rural contexts, and in temperate and tropical climes. Leptospirosis is a disease of the environment; transmission depends on interactions between humans and mammalian reservoir hosts. A variety of infectious diseases that present as undifferentiated febrile syndromes, such as malaria, dengue and influenza, as well as viral hemorrhagic fevers can mimic leptospirosis. The importance of pulmonary hemorrhage as a lethal complication of leptospirosis has become more widely recognized. In contrast to textbook dogma, population-based studies indicate that there is a poor correlation between infecting leptospiral strain and clinical expression of disease. Genetic transformation of a Leptospira sp. has now been reported, which should allow for detailed analysis of a variety of leptospiral genes. Publication of the whole Leptospira genome is eagerly awaited. Following recent reports of a new, highly effective conjugate typhoid vaccine, new efforts to find leptospirosis vaccines should include the manufacture and testing of conjugate leptospiral lipopolysaccharide vaccines. Recent advances, particularly in epidemiology, molecular genetics and pathogenesis, are placing leptospirosis at the cutting edge of biomedical science.
Asunto(s)
Leptospirosis/epidemiología , Técnicas de Tipificación Bacteriana , Humanos , Leptospira/clasificación , Leptospira/genética , Leptospira/patogenicidad , Leptospirosis/diagnóstico , Leptospirosis/tratamiento farmacológicoRESUMEN
Plasmodium ookinetes secrete chitinases to penetrate the acellular, chitin-containing peritrophic matrix of the mosquito midgut en route to invasion of the epithelium. Chitinases are potentially targets that can be used to block malaria transmission. We demonstrate here that chitinases of Plasmodium falciparum and P. gallinaceum are concentrated at the apical end of ookinetes. The chitinase PgCHT1 of P. gallinaceum is present within ookinete micronemes and subsequently becomes localized in the electron-dense area of the apical complex. These observations suggest a pathway by which ookinetes secrete proteins extracellularly.
Asunto(s)
Quitinasas/metabolismo , Plasmodium/metabolismo , Animales , Transporte Biológico , Microscopía Fluorescente , Microscopía Inmunoelectrónica , Plasmodium/ultraestructuraRESUMEN
The Plasmodium ookinete produces chitinolytic activity that allows the parasite to penetrate the chitin-containing peritrophic matrix surrounding the blood meal in the mosquito midgut. Since the peritrophic matrix is a physical barrier that the parasite must cross to invade the mosquito, and the presence of allosamidin, a chitinase inhibitor, in a blood meal prevents the parasite from invading the midgut epithelium, chitinases (3.2.1.14) are potential targets of malaria parasite transmission-blocking interventions. We have purified a chitinase of the avian malaria parasite Plasmodium gallinaceum and cloned the gene, PgCHT1, encoding it. PgCHT1 encodes catalytic and substrate-binding sites characteristic of family 18 glycohydrolases. Expressed in Escherichia coli strain AD494 (DE3), recombinant PgCHT1 was found to hydrolyze polymeric chitin, native chitin oligosaccharides, and 4-methylumbelliferone derivatives of chitin oligosaccharides. Allosamidin inhibited recombinant PgCHT1 with an IC(50) of 7 microM and differentially inhibited two chromatographically separable P. gallinaceum ookinete-produced chitinase activities with IC(50) values of 7 and 12 microM, respectively. These two chitinase activities also had different pH activity profiles. These data suggest that the P. gallinaceum ookinete uses products of more than one chitinase gene to initiate mosquito midgut invasion.
Asunto(s)
Quitinasas/genética , Quitinasas/metabolismo , Culicidae/parasitología , Plasmodium gallinaceum/fisiología , Secuencia de Aminoácidos , Animales , Pollos , Quitinasas/aislamiento & purificación , Secuencia de Consenso , Sistema Digestivo/parasitología , Células Epiteliales/enzimología , Regulación del Desarrollo de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Humanos , Cinética , Malaria Aviar , Datos de Secuencia Molecular , Plasmodium gallinaceum/genética , Plasmodium gallinaceum/patogenicidad , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/química , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
To identify potential zoonotic reservoirs of pathogenic leptospires in the Peruvian Amazon basin, wild mammals were trapped from July 1997 to December 1998 near the city of Iquitos. After extraction of nucleic acids from animal kidneys, DNA of pathogenic leptospires was identified by polymerase chain reaction (PCR) assays using one of two primer sets, one amplifying a region of the 23S rRNA gene, and the other amplifying a gene fragment specific for Leptospira spp (G1/G2 primers). Overall, 29% (40 of 136) of the mammals tested showed evidence of renal infection by Leptospira spp., including 20% (13 of 64) of the rodents, 39% (20 of 51) of the marsupials, and 35% (7 of 20) of the chiropterans (bats). Marsupials and chiropterans were implicated as more significant reservoir hosts of leptospires pathogenic to humans than previously recognized.
Asunto(s)
ADN Bacteriano/aislamiento & purificación , Reservorios de Enfermedades , Leptospira/aislamiento & purificación , Leptospirosis/veterinaria , Mamíferos , Animales , Carnívoros , Quirópteros , Cartilla de ADN , Leptospira/genética , Leptospirosis/epidemiología , Marsupiales , Perú/epidemiología , Reacción en Cadena de la Polimerasa/veterinaria , RoedoresRESUMEN
Within hours after the ingestion of a blood meal, the mosquito midgut epithelium synthesizes a chitinous sac, the peritrophic matrix. Plasmodium ookinetes traverse the peritrophic matrix while escaping the mosquito midgut. Chitinases (EC 3.2.1.14) are critical for parasite invasion of the midgut: the presence of the chitinase inhibitor, allosamidin, in an infectious blood meal prevents oocyst development. A chitinase gene, PgCHT1, recently has been identified in the avian malaria parasite P. gallinaceum. We used the sequence of PgCHT1 to identify a P. falciparum chitinase gene, PfCHT1, in the P. falciparum genome database. PfCHT1 differs from PgCHT1 in that the P. falciparum gene lacks proenzyme and chitin-binding domains. PfCHT1 was expressed as an active recombinant enzyme in Escherichia coli. PfCHT1 shares with PgCHT1 a substrate preference unique to Plasmodium chitinases: the enzymes cleave tri- and tetramers of GlcNAc from penta- and hexameric oligomers and are unable to cleave smaller native chitin oligosaccharides. The pH activity profile of PfCHT1 and its IC(50) (40 nM) to allosamidin are distinct from endochitinase activities secreted by P. gallinaceum ookinetes. Homology modeling predicts that PgCHT1 has a novel pocket in the catalytic active site that PfCHT1 lacks, which may explain the differential sensitivity of PfCHT1 and PgCHT1 to allosamidin. PfCHT1 may be the ortholog of a second, as yet unidentified, chitinase gene of P. gallinaceum. These results may allow us to develop novel strategies of blocking human malaria transmission based on interfering with P. falciparum chitinase.
Asunto(s)
Quitina/metabolismo , Quitinasas/genética , Precursores Enzimáticos/genética , Plasmodium falciparum/enzimología , Acetilglucosamina/análogos & derivados , Acetilglucosamina/farmacología , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión , Quitinasas/antagonistas & inhibidores , Quitinasas/química , Quitinasas/metabolismo , Activación Enzimática , Inhibidores Enzimáticos/farmacología , Precursores Enzimáticos/antagonistas & inhibidores , Precursores Enzimáticos/química , Precursores Enzimáticos/metabolismo , Expresión Génica , Genes Protozoarios , Humanos , Concentración de Iones de Hidrógeno , Malaria/parasitología , Modelos Moleculares , Datos de Secuencia Molecular , Plasmodium falciparum/genética , Conformación Proteica , Proteínas Protozoarias , Homología de Secuencia de Aminoácido , Especificidad por Sustrato , Trisacáridos/farmacologíaRESUMEN
Pathogens causing a number of human and animal diseases use chitin and chitinases in their life cycles. Most of these diseases are caused by protozoan or metazoan pathogenic parasites. Some of these parasites contain chitin coats that protect them from the harsh conditions in the animal body or the environment. Some pathogens use chitinase to invade or exploit the chitin-containing structures of their host to establish successful infection or to be transmitted from one vertebrate to another via insect vectors. Recent studies indicate that each of these organisms has evolved to use chitin and chitinases differently and in a developmental stage-specific manner. Genes of many of these pathogenic parasites have been isolated, and the predicted amino acid sequences show a great deal of diversity. In this chapter we will discuss the roles chitin and chitinases play in several animal diseases, the strategies used to clone the chitinase genes from various parasites and the usefulness of chitinases as preventive or therapeutic agents.
Asunto(s)
Quitinasas/genética , Parásitos/fisiología , Enfermedades Parasitarias/terapia , Animales , Antiparasitarios/uso terapéutico , Quitina/metabolismo , Quitinasas/metabolismo , Diseño de Fármacos , Inhibidores Enzimáticos/uso terapéutico , Humanos , Parásitos/enzimología , Parásitos/genética , Enfermedades Parasitarias/prevención & control , VacunasAsunto(s)
Malaria/diagnóstico , Metotrexato/efectos adversos , Plasmodium malariae , Esplenomegalia/etiología , Anciano , Animales , Anticuerpos Antiprotozoarios/sangre , Secuencia de Bases , Diagnóstico Diferencial , Femenino , Grecia , Humanos , Linfoma/diagnóstico , Linfoma/tratamiento farmacológico , Malaria/complicaciones , Datos de Secuencia Molecular , Plasmodium malariae/genética , Plasmodium malariae/inmunologíaRESUMEN
BACKGROUND: Surprisingly, many inner-city residents have antibodies to Leptospira interrogans. The manner in which these persons acquire this organism in the absence of recognized occupational, recreational, or epidemic risk factors is not known. OBJECTIVE: To study the epidemiology of patients with leptospirosis who acquired L. interrogans in inner-city Baltimore, Maryland. DESIGN: Epidemiologic investigation. SETTING: Inner-city university hospital. PATIENTS: Three inner-city residents who developed leptospirosis. MEASUREMENTS: Trapping rats in alleys where the patients may have acquired L. interrogans; polymerase chain reaction (PCR) analysis of patients serum and cerebrospinal fluid specimens and rat tissues to determine the presence of leptospiral DNA; and serologic testing of serum from patients and rats by microagglutination assay to confirm L. interrogans infection. RESULTS: Three patients developed leptospirosis after probable percutaneous exposure to rat (Rattus norvegicus) urine in Baltimore alleys. A PCR assay detected L. interrogans DNA in samples of body fluid obtained from the first two patients at presentation (one in cerebrospinal fluid, the other in serum). Results of PCR done on serum drawn from the third patient after antibiotic therapy began were negative. A microagglutination test showed that all patients had high levels of antibodies to the L. interrogans serogroup icterohaemorrhagiae. In 19 of 21 rats that were trapped in the alleys where the patients had sustained lacerations before illness developed, kidney or brain tissues were positive by PCR for the presence of L. interrogans. CONCLUSIONS: A population was discovered to be at risk for acquiring L. interrogans: urban residents who are sporadically exposed to rat urine in the inner city. Inner-city rats often carry L. interrogans. Polymerase chain reaction can quickly establish the diagnosis of leptospirosis and is useful for epidemiologic study. An endemic substrate for the transmission of the organism is present in inner-city Baltimore. Leptospirosis may become increasingly recognized in deteriorating inner cities in which rat populations are expanding.
Asunto(s)
Leptospirosis/epidemiología , Salud Urbana , Adulto , Animales , Anticuerpos Antibacterianos/análisis , Baltimore/epidemiología , ADN Bacteriano/análisis , Vectores de Enfermedades , Femenino , Humanos , Leptospira interrogans/aislamiento & purificación , Leptospirosis/diagnóstico , Leptospirosis/transmisión , Masculino , Reacción en Cadena de la Polimerasa , Ratas/microbiología , Ratas/orina , Factores de RiesgoRESUMEN
OBJECTIVE: To define clinical and laboratory variables that suggest the presence of Clostridium difficile colitis and to establish the number of stool specimens needed to reasonably exclude the diagnosis of C. difficile colitis. DESIGN: Prospective study of consecutive inpatients whose stool specimens were sent to be evaluated for the presence of C. difficile toxin. SETTING: University teaching hospital. PATIENTS: 268 hospital inpatients in medical, surgical, and gynecology units. MEASUREMENTS: Structured history and physical examination; detection of C. difficile toxin by cytotoxin tissue-culture assay with anti-C. difficile antiserum neutralization and by enzyme-linked immunoassay (EIA) for C. difficile toxins A and B; and detection of fecal leukocytes by microscopic examination and by latex agglutination lactoferrin assay. RESULTS: 43 of 268 consecutive inpatients were positive for C. difficile toxin by EIA or tissue-culture assay. Although toxin was detected by EIA alone in 39 of the 43 patients, it was detected in an additional 4 patients (10%) by tissue-culture assay alone. Univariate and multivariate logistic regression analysis showed that the following clinical and laboratory features were associated with C. difficile toxin positivity: the onset of diarrhea 6 or more days after the administration of antibiotics (odds ratio, 1.38 [95% CI, 1.10 to 3.79]); hospital stay longer than 15 days (odds ratio, 1.33 [CI, 1.09 to 3.95]); the presence of fecal leukocytes determined by microscopy (odds ratio, 2.39 [CI, 1.05 to 5.42]) or lactoferrin assay (odds ratio, 3.74 [CI, 1.80 to 7.76]); the presence of semiformed (as opposed to watery) stools (odds ratio, 2.33 [CI, 1.10 to 4.90]); and cephalosporin use (odds ratio, 2.36 [CI, 1.10 to 5.09]). Toxin-positive patients were no more likely than controls to have had fever, abdominal pain or cramps, leukocytosis, green-colored diarrhea, or blood in the stool or to have received clindamycin or penicillin derivatives. Of the 43 patients with C. difficile toxin, 34 (79%) had positive results for the toxin on the first stool specimen, 5 (cumulative, 91%) had positive results on the second specimen, and 4 had positive results on the third specimen. Overall, the negative predictive value of the first stool specimen was 97%. All patients who had two or more clinical or laboratory predictors were diagnosed with C. difficile disease when either the first or the second stool specimen was positive for toxin. CONCLUSIONS: Clinicians at the bedside can use readily available clinical and laboratory information to decide which patients are likely to have C. difficile disease and when it is appropriate and useful to order specific diagnostic tests for C. difficile toxin. Such data are also useful in determining the number of stool samples that reasonably excludes the diagnosis of C. difficile colitis.
Asunto(s)
Clostridioides difficile/aislamiento & purificación , Infecciones por Clostridium/diagnóstico , Colitis/diagnóstico , Anciano , Análisis de Varianza , Toxinas Bacterianas/análisis , Colitis/microbiología , Heces/microbiología , Femenino , Humanos , Inmunoensayo , Técnicas para Inmunoenzimas , Recuento de Leucocitos , Masculino , Persona de Mediana Edad , Oportunidad Relativa , Estudios Prospectivos , Análisis de Regresión , Sensibilidad y EspecificidadRESUMEN
Infection of mice with the malaria parasite Plasmodium vinckei vinckei is 100% lethal. However, after two infections followed by drug cure, BALB/c mice develop a solid immunity which is antibody independent but mediated by CD4+ T cells. To elucidate the mechanisms of this immunity, spleen cells from immune mice were challenged in vitro with lysates of P. vinckei-infected or uninfected erythrocytes. The parasite antigen induced proliferation of T cells from immune mice but not from nonimmune mice. When gamma interferon production by cells from immune mice was assayed at the single-cell level, 1 to 3 cells per 1,000 cells were found to release this cytokine when exposed to antigen. In contrast, the numbers of interleukin 4 (IL-4)-producing cells from both immune and control mice were < or = 4 per 10(6) cells, regardless of antigen exposure. Investigation in a bioassay showed that P. vinckei antigen induced the release of IL-4 from spleen cells of immune mice but not from those of control mice. Nevertheless, that IL-4 is of minor significance in this system is also suggested by the absence of elevation of immunoglobulin E levels in blood samples from these mice, in contrast to what is seen with P. chabaudi infection, in which IL-4-producing Th2 cells are of major importance for immunity during later phases of infection. Taken together, the present results indicate that immunity to P. vinckei is a Th1 response, with gamma interferon being an important protective factor. Whether or not the Th1 response, through overproduction of tumor necrosis factor alpha, is also responsible for pathology and death in this infection remains to be clarified.