Tumour necrosis factor and associated cytokines in the host's response to malaria

Is TNF alpha a mediator in the co-existence of malaria and type 2 diabetes in a malaria endemic population?

Malaria remains a disease of public health importance globally, especially in sub-Saharan Africa. Malaria deaths reduced globally steadily between 2000-2019, however there was a 10% increase in 2020 due to disruptions in medical service during the COVID-19 pandemic. Globally, about 96% of malaria deaths occurred in 29 countries; out of which, four countries (Nigeria, the Democratic Republic of the Congo, the Niger, and the United Republic of Tanzania) accounted for just over half of the malaria deaths. Nigeria leads the four countries with the highest malaria deaths (accounting for 31% globally). Parallelly, sub-Saharan Africa is faced with a rise in the incidence of Type 2 diabetes (T2D). Until recently, T2D was a disease of adulthood and old age. However, this is changing as T2D in children and adolescents is becoming an increasingly important public health problem. Nigeria has been reported to have the highest burden of diabetes in Africa with a prevalence of 5.77% in the country. Several studies conducted in the last decade investigating the interaction between malaria and T2D in developing countries have led to the emergence of the intra-uterine hypothesis. The hypothesis has arisen as a possible explanation for the rise of T2D in malaria endemic areas; malaria in pregnancy could lead to intra-uterine stress which could contribute to low birth weight and may be a potential cause of T2D later in life. Hence, previous, and continuous exposure to malaria infection leads to a higher risk of T2D. Current and emerging evidence suggests that an inflammation-mediated link exists between malaria and eventual T2D emergence. The inflammatory process thus, is an important link for the co-existence of malaria and T2D because these two diseases are inflammatory-related. A key feature of T2D is systemic inflammation, characterized by the upregulation of inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) which leads to impaired insulin signaling. Malaria infection is an inflammatory disease in which TNF-α also plays a major role. TNF-α plays an important role in the pathogenesis and development of malaria and T2D. We therefore hypothesize that TNF-α is an important link in the increasing co-existence of T2D.

Effect of Formulated Artocarpus champeden Extract on Parasite Growth and Immune Response of Plasmodium berghei-Infected Mice

Background

The ethanol extract of Artocarpus champeden stem bark (ACEE) has been proven to exhibit antimalarial activity. Despite the antimalarial effects observed, mechanisms of immune response to explain the antimalarial activity of ACEE remain poorly characterized. Here, we show the production of pro- and anti-inflammatory cytokines T helper 1 (Th1: IFN-γ, TNF-α) and T helper 2 (Th2: IL-10) from Plasmodium berghei-infected mice treated with formulated ACEE in order to better characterize the mechanism behind ACEE's antimalarial activity. In addition, we have also determined the effect of formulated ACEE on parasite growth and liver function.

Methods

Balb/c mice were infected with P. berghei strain ANKA and then administered daily doses of ACEE at a dose of 20, 50, and 100 mg/kg BW, and survival time was recorded. We determined the presence of P. berghei strain ANKA and then administered daily doses of ACEE at a dose of 20, 50, and 100 mg/kg BW, and survival time was recorded. We determined the presence of P. berghei strain ANKA and then administered daily doses of ACEE at a dose of 20, 50, and 100 mg/kg BW, and survival time was recorded. We determined the presence of γ, TNF-α) and T helper 2 (Th2: IL-10) from

Results

We found that formulated ACEE inhibited parasite growth and showed the highest antimalarial activity at 100 mg/kg BW. AST and ALT levels were found to be in the normal range, and there was no significant difference among control and treatment groups (P > 0.05). Infected mice treated with formulated ACEE showed a significant increase in the production of IFN-γ, TNF-α) and T helper 2 (Th2: IL-10) from

Conclusion

This study suggests that the administration of ACEE was effective in inhibiting P. berghei strain ANKA and then administered daily doses of ACEE at a dose of 20, 50, and 100 mg/kg BW, and survival time was recorded. We determined the presence of γ, TNF-α) and T helper 2 (Th2: IL-10) from

The systemic pathology of cerebral malaria in African children

Pediatric cerebral malaria carries a high mortality rate in sub-Saharan Africa. We present our systematic analysis of the descriptive and quantitative histopathology of all organs sampled from a series of 103 autopsies performed between 1996 and 2010 in Blantyre, Malawi on pediatric cerebral malaria patients and control patients (without coma, or without malaria infection) who were clinically well characterized prior to death. We found brain swelling in all cerebral malaria patients and the majority of controls. The histopathology in patients with sequestration of parasites in the brain demonstrated two patterns: (a) the “classic” appearance (i.e., ring hemorrhages, dense sequestration, and extra-erythrocytic pigment) which was associated with evidence of systemic activation of coagulation and (b) the “sequestration only” appearance associated with shorter duration of illness and higher total burden of parasites in all organs including the spleen. Sequestration of parasites was most intense in the gastrointestinal tract in all parasitemic patients (those with cerebral malarial and those without).

Role of IL6, IL12B and VDR gene polymorphisms in Plasmodium vivax malaria severity, parasitemia and gametocytemia levels in an Amazonian Brazilian population

OBJECTIVE

To investigate the influence of IL6, IL12B and VDR single nucleotide polymorphisms (SNPs) in uncomplicated Plasmodium vivax infection symptoms intensity, parasitemia and gametocytemia levels in a Brazilian Amazonian population.

METHODS

A total of 167 malaria patients infected by P. vivax have parasitemia and gametocytemia levels estimated before treatment. Fourteen clinical symptoms were evaluated and included in a principal component analysis to derive a clinical symptom index. Patients were genotyped for IL6-174C>G, IL12B 735T>C, 458A>G, 159A>C, and VDR FokI, TaqI, BsmI SNPs by Taqman 5' nuclease assays. A General Linear Model analysis of covariance with age, gender, exposure period and infection history and genetic ancestry was performed to investigate the association of genotypes with parasitemia and gametocytemia levels and with a clinical symptom index.

RESULTS

Higher parasitemia levels were observed in IL6-174C carriers (p=0.02) whereas IL12B CGT haplotype carriers presented lower parasitemia levels (p=0.008). VDR TaqIC/BsmIA haplotype carriers showed higher gametocyte levels than non-carriers (p=0.013). Based on the clinical index values the IL6-174C>G polymorphism was associated with malaria severity. The IL6-174C carriers presented a more severe clinical index when compared to GG homozygotes (p=0.001).

CONCLUSION

The present study suggests that IL6, IL12 and VDR influence severity, parasitemia and gametocytemia clearance in P. vivax infections, and highlights their potential role in malaria immune response in an Amazonian population.

Expression of non-TLR pattern recognition receptors in the spleen of BALB/c mice infected with Plasmodium yoelii and Plasmodium chabaudi chabaudi AS

The spleen plays a crucial role in the development of immunity to malaria, but the role of pattern recognition receptors (PRRs) in splenic effector cells during malaria infection is poorly understood. In the present study, we analysed the expression of selected PRRs in splenic effector cells from BALB/c mice infected with the lethal and non-lethal Plasmodium yoelii strains 17XL and 17X, respectively, and the non-lethal Plasmodium chabaudi chabaudi AS strain. The results of these experiments showed fewer significant changes in the expression of PRRs in AS-infected mice than in 17X and 17XL-infected mice. Mannose receptor C type 2 (MRC2) expression increased with parasitemia, whereas Toll-like receptors and sialoadhesin (Sn) decreased in mice infected with P. chabaudi AS. In contrast, MRC type 1 (MRC1), MRC2 and EGF-like module containing mucin-like hormone receptor-like sequence 1 (F4/80) expression decreased with parasitemia in mice infected with 17X, whereas MRC1 an MRC2 increased and F4/80 decreased in mice infected with 17XL. Furthermore, macrophage receptor with collagenous structure and CD68 declined rapidly after initial parasitemia. SIGNR1 and Sn expression demonstrated minor variations in the spleens of mice infected with either strain. Notably, macrophage scavenger receptor (Msr1) and dendritic cell-associated C-type lectin 2 expression increased at both the transcript and protein levels in 17XL-infected mice with 50% parasitemia. Furthermore, the increased lethality of 17X infection in Msr1 -/- mice demonstrated a protective role for Msr1. Our results suggest a dual role for these receptors in parasite clearance and protection in 17X infection and lethality in 17XL infection.

Nitric oxide is involved in the upregulation of IFN-γ and IL-10 mRNA expression by CD8⁺ T cells during the blood stages of P. chabaudi AS infection in CBA/Ca mice

Nitric oxide (NO) is involved in the clearance of several types of bacteria, viruses and parasites. Although the roles of NO and CD8⁺ T cells in the immune response to malaria have been extensively studied, their actual contributions during the blood stages of malaria infection remain unclear.

In this work, we corroborate that serum NO levels are not associated with the in vivo elimination of the blood stages of Plasmodium chabaudi AS. In addition, we show that CD8⁺ T cells exhibit increased apoptosis and up regulate the expression of TNF-α mRNA on day 4 post-infection and IFN-γ and IL-10 mRNA on day 11 post-infection. Interestingly, only the levels of IFN-γ and IL-10 expression are affected when iNOS is inhibited with aminoguanidine (AG), suggesting that NO could be involved in the activation of CD8⁺ T cells during the blood stages of plasmodium infection.

Amplification of P. falciparum Cytoadherence through induction of a pro-adhesive state in host endothelium

This study examined the ability of P.falciparum-infected erythrocytes (IE) to induce a pro-adhesive environment in the host endothelium during malaria infection, prior to the systemic cytokine activation seen in the later phase of disease. Previous work had shown increases in receptor levels but had not measured to actual impact on IE binding. Using a co-culture system with a range of endothelial cells (EC) and IE with different cytoadherent properties, we have characterised the specific expression of adhesion receptors and subsequent IE binding by FACS and adhesion assays. We have also examined the specific signalling pathways induced during co-culture that are potentially involved in the induction of receptor expression. The results confirmed that ICAM-1 is up-regulated, albeit at much lower levels than seen with TNF activation, in response to co-culture with infected erythrocytes in all three tissue endothelial cell types tested but that up-regulation of VCAM-1 is tissue-dependent. This small increase in the levels of EC receptors correlated with large changes in IE adhesion ability. Co-culture with either RBC or IE increased the potential of subsequent adhesion indicating priming/modulation effects on EC which make them more susceptible to adhesion and thereby the recruitment of IE. Trypsin surface digestion of IE and the use of a Pfsbp1-knockout (ko) parasite line abrogated the up-regulation of ICAM-1 and reduced IE binding to EC suggesting that PfEMP-1 and other molecules exported to the IE surface via the PfSBP1 pathway are major mediators of this phenotype. This was also supported by the higher induction of EC adhesion receptors by adherent IE compared to isogenic, non-adherent lines.

Iron deficiency anemia: focus on infectious diseases in lesser developed countries

Iron deficiency anemia is thought to affect the health of more than one billion people worldwide, with the greatest burden of disease experienced in lesser developed countries, particularly women of reproductive age and children. This greater disease burden is due to both nutritional and infectious etiologies. Individuals in lesser developed countries have diets that are much lower in iron, less access to multivitamins for young children and pregnant women, and increased rates of fertility which increase demands for iron through the life course. Infectious diseases, particularly parasitic diseases, also lead to both extracorporeal iron loss and anemia of inflammation, which decreases bioavailability of iron to host tissues. This paper will address the unique etiologies and consequences of both iron deficiency anemia and the alterations in iron absorption and distribution seen in the context of anemia of inflammation. Implications for diagnosis and treatment in this unique context will also be discussed.

Associations between peripheral Plasmodium falciparum malaria parasitemia, human immunodeficiency virus, and concurrent helminthic infection among pregnant women in Malawi

Approximately 2 billion persons worldwide are infected with schistosomiasis and soil-transmitted helminths (STH), many in areas where endemic malaria transmission coexists. Few data exist on associations between these infections. Nested within a larger clinical trial, primigravid and secundigravid women provided blood samples for human immunodeficiency virus (HIV) testing and peripheral malaria films and stool and urine for evaluation of STH and Schistosoma spp. during their initial antenatal clinic visit. The most common parasitic infections were malaria (37.6%), S. haematobium (32.3%), and hookworm (14.4%); 14.2% of women were HIV-infected. S. haematobium infection was associated with lower malarial parasite densities (344 versus 557 parasites/μL blood; P < 0.05). In multivariate analysis, HIV and hookworm infection were independently associated with malaria infection (adjusted odds ratio = 1.9 and 95% confidence interval = 1.2-3.0 for HIV; adjusted odds ratio = 1.9 and 95% confidence interval = 1.03-3.5 for hookworm). Concurrent helminthic infection had both positive and negative effects on malaria parasitemia among pregnant women in Malawi.

Fatal Myocarditis in Course of Plasmodium falciparum Infection: Case Report and Review of Cardiac Complications in Malaria

We describe a fatal case of imported malaria where the sole finding revealed at the postmortem evaluation was an acute lymphocytic myocarditis with myocardiolysis. This case recalls the potential importance of myocardial injury in the prognosis of malaria and prompts a reevaluation of current perspectives on the pathogenesis of severe falciparum infection. In the light of this, we have reviewed the cases of cardiac complications in malaria published to date.

A preliminary study on pro- and anti-inflammatory cytokine profiles in Plasmodium vivax malaria patients from central zone of India

The aim of this preliminary study was to investigate the plasma cytokine profiles in a group of patients suffering from Plasmodium vivax malaria during the peak of its transmission season. Plasma samples of 173 P. vivax patients and 34 healthy individuals were analyzed for IFN-gamma, TNF-alpha, IL-10 and IP-10 levels by ELISA. Levels of both pro- and anti-inflammatory cytokines were significantly higher in P. vivax patients compared to controls. Children with P. vivax infection had significantly higher levels of IFN-gamma than adults (P=0.017). Asexual parasitaemia versus TNF-alpha (r=-0.31, P=0.01), IL-10 (r=-0.30, P=0.015) and gametocytaemia versus IFN-gamma (r=-0.26; P=0.034) levels showed significant negative correlation in children compared to adults. The median concentrations of IFN-gamma (P=0.001), IL-10 (P=0.032) and IP-10 (P</=0.05) were higher in children reported with chills and rigors, whereas in adults only IFN-gamma levels was higher (P<0.0001). The median plasma concentrations of IFN- gamma (P=0.02), IL-10 (P<0.0001) and IP-10 (P=0.068) were higher in patients with mild anaemia compared to non-anaemic patients. The results indicated that both pro- and anti-inflammatory cytokine responses are associated with clinical signs of mild anaemia and paroxysm during symptomatic P. vivax malaria in Central India.

Cellular tumor necrosis factor, gamma interferon, and interleukin-6 responses as correlates of immunity and risk of clinical Plasmodium falciparum malaria in children from Papua New Guinea

The role of early to intermediate Plasmodium falciparum-induced cellular responses in the development of clinical immunity to malaria is not well understood, and such responses have been proposed to contribute to both immunity and risk of clinical malaria episodes. To investigate whether P. falciparum-induced cellular responses are able to function as predictive correlates of parasitological and clinical outcomes, we conducted a prospective cohort study of children (5 to 14 years of age) residing in a region of Papua New Guinea where malaria is endemic Live, intact P. falciparum-infected red blood cells were applied to isolated peripheral blood mononuclear cells obtained at baseline. Cellular cytokine production, including production of interleukin-2 (IL-2), IL-4, IL-6, IL-10, tumor necrosis factor (TNF) (formerly tumor necrosis factor alpha), and gamma interferon (IFN-gamma), was measured, and the cellular source of key cytokines was investigated. Multicytokine models revealed that increasing P. falciparum-induced IL-6 production was associated with an increased incidence of P. falciparum clinical episodes (incidence rate ratio [IRR], 1.75; 95% confidence interval [CI], 1.20 to 2.53), while increasing P. falciparum-induced TNF and IFN-gamma production was associated with a reduced incidence of clinical episodes (IRR for TNF, 0.55 [95% CI, 0.38 to 0.80]; IRR for IFN-gamma, 0.71 [95% CI, 0.55 to 0.90]). Furthermore, we found that monocytes/macrophages and gammadelta-T cells are important for the P. falciparum-induced production of IL-6 and TNF. Early to intermediate cellular cytokine responses to P. falciparum may therefore be important correlates of immunity and risk of symptomatic malaria episodes and thus warrant detailed investigation in relation to the development and implementation of effective vaccines.

Lymphotoxin alpha and tumour necrosis factor are not required for control of parasite growth, but differentially regulate cytokine production during Plasmodium chabaudi chabaudi AS infection

Tumour necrosis factor (TNF) plays important roles in the pathogenesis of severe malaria, as well as in the generation of immune responses against malaria parasites. However, far less is known about the role of the closely related TNF family member lymphotoxin alpha (LTalpha) during malaria. We have used mice deficient in either TNF or LTalpha, as well as chimeric mice generated using donor bone marrow from these animals, to study the roles of these cytokines following Plasmodium chabaudi chabaudi AS infection. TNF and LTalpha were not required for the resolution of P. chabaudi chabaudi AS blood-stage infection. However, LTalpha, but not TNF, was necessary for early IFNgamma production and the regulation of IFNgamma production later in infection. A similar delay to that found for IFNgamma production was also observed for TNF production in LTalpha-deficient mice, compared with control mice. These results identify divergent roles for TNF and LTalpha in the regulation of host immune responses during P. chabaudi chabaudi AS infection.

Serum cytokine profiles in patients with Plasmodium vivax malaria: a comparison between those who presented with and without hepatic dysfunction

The aim of this study was to compare the serum cytokine profiles of Plasmodium vivax malaria patients who presented with and without hepatic dysfunction. This is a retrospective analysis of 74 consecutive cases of P. vivax malaria seen at 3 military hospitals near the Demilitarized Zone in South Korea from 1999 to 2000. All patients studied were adult active duty servicemen. On admission, the mean (+/- SEM) age of the patients who presented with (n = 36) and without hepatic dysfunction (n = 38) was 21.6 +/- 0.24 and 22.5 +/- 0.44 years, respectively (P = 0.72). On admission, there was no significant difference between the 2 patient populations in terms of mean temperature, haemoglobin level, haematocrit, total white blood cell count, platelet count, parasite index, and serum concentration of transforming growth factor-beta. Plasmodium vivax malaria patients who presented with hepatic dysfunction had significantly higher mean serum concentrations of soluble Fas ligand, interleukin (IL)-l, IL-4, IL-6, IL-10, tumor necrosis factor-alpha, and interferon-gamma than those without hepatic dysfunction, suggesting the involvement of these cytokines in the development of hepatic dysfunction. The mean serum concentration of IL-12 was significantly lower in patients with hepatic dysfunction. The mean body temperature was not significantly different between the 2 patient populations.

The association of anti-phospholipid antibodies with parity in placental malaria

Anti-phospholipid antibodies (aPL) are autoantibodies associated with both infections and the pathogenesis of certain pregnancy complications. In the latter, but not the former, aPL are dependent on a co-factor, beta(2) glycoprotein I (beta2GPI), which can also be used as an antigen for detection of such aPL in pregnancy. A cross-sectional study was carried out on serum samples from Kumasi, Ghana, to determine the occurrence and beta2GPI-dependence of aPL in placental malaria. Anti-cardiolipin, anti-phosphatidylserine and anti-beta2GPI enzyme-linked immunosorbent assays (ELISAs) were performed on sera from 103 HIV-non-infected gravid women. Placental malaria, both active and past infection, was diagnosed in 33/103 (32%) based on placental histology. In multiparae, beta2GPI-independent IgM antibodies to cardiolipin (P = 0.018) and phosphatidylserine (P = 0.009) were observed, which were most pronounced in past placental malaria infection. In primiparae, no association emerged between aPL and placental malaria. Trends for improved clinical parameters were identified in infected women with levels of anti-cardiolipin beyond the 99th multiple of the median for a healthy, non-malarious population. This study in placental malaria reports parity associations of beta2GPI-independent aPL profiles, and does not support a role for beta2GPI-dependent aPL. It is of significance in the context of the known parity differences in pregnancy malaria immunity.

Chronic estradiol and progesterone treatment in conscious dogs: effects on insulin sensitivity and response to hypoglycemia

We evaluated the effect of chronic (3 wk) subcutaneous treatment with progesterone and estradiol (PE; producing serum levels observed in the 3rd trimester of pregnancy) or placebo (C) on hepatic and whole body insulin sensitivity and response to hypoglycemia in conscious, overnight-fasted nonpregnant female dogs, using tracer and arteriovenous difference techniques. Insulin was infused peripherally for 3 h at 1.8 mU x kg(-1) x min(-1). Glucose was allowed to fall to 3 mM (Hypo) or maintained at 6 mM (Eugly) by peripheral glucose infusion. Insulin concentrations were significantly higher in Eugly-PE (n = 7) and Hypo-PE (n = 7) than in Eugly-C (n = 6) and Hypo-C groups (n = 7), but there were no significant differences in hepatic insulin extraction. Concentrations of glucagon, cortisol, epinephrine, and norepinephrine did not differ significantly between Eugly groups or between Hypo groups. Whole body glucose disposal, adjusted for the differences in insulin between groups, was 35% higher in Eugly-C vs. Eugly-PE groups (P < 0.05). Eugly-C and Eugly-PE groups exhibited similar rates of net hepatic glucose uptake, but the rate of glucose appearance was greater in Eugly-PE in the last hour (P < 0.05). Net hepatic glucose output was greater (P < 0.05) in Hypo-PE than in Hypo-C groups, and the glucose infusion rate required to maintain equivalent hypoglycemia was less (P < 0.05). The rate of gluconeogenic flux did not differ between Hypo groups. Chronic progesterone and estradiol exposure caused whole body (primarily skeletal muscle) insulin resistance and enhanced the liver's response to hypoglycemia without altering counterregulatory hormone concentrations.

The epidemiology and consequences of maternal malaria: a review of immunological basis

Millions of women who become pregnant in malaria-endemic areas are at increased risk of contracting malaria infection that jeopardises the outcome of pregnancy. The complication of this infection for mother and baby are considerable. In absence of any other reason, it was thought that the increased risk of infection during pregnancy was related to suppression of pre-existing malaria immunity. Although this concept is plausible, the significantly higher risk of maternal malaria and consequences in primigravidae compared with multigravidae suggests that there are more to mere immunosuppression in pregnancy. The mechanisms underlying some of the striking epidemiological and clinical features of malaria in pregnancy could be related to differences in the strains of parasite populations infecting pregnant women occasioned by the cyto-adherent properties of human placenta, presence or absence of anti-adhesion antibodies acquired from previous pregnancies or the elevated production of some pro-inflammatory cytokines in response to parasitisation of human placenta. Malaria infection of placenta causes a shift from Th2 to Th1 cytokine profile that may be detrimental to pregnancy. The increased susceptibility in the first pregnancy can be explained by the absence of anti-adhesion antibody in the primigravida that is being exposed for the first time to a different strain of malaria parasite sub-population that adhere exclusively to chondroitin sulphate A and hyaluronic acid (HA) in the placenta. In reviewing the epidemiology and consequences of maternal malaria, we have highlighted possible immunological and molecular basis that could account for the higher impact of malaria in pregnancy especially among primigravidae. These factors could be the basis for future research and vaccine formulation.

Mammalian transforming growth factor beta1 activated after ingestion by Anopheles stephensi modulates mosquito immunity

During the process of bloodfeeding by Anopheles stephensi, mammalian latent transforming growth factor beta1 (TGF-beta1) is ingested and activated rapidly in the mosquito midgut. Activation may involve heme and nitric oxide (NO), agents released in the midgut during blood digestion and catalysis of L-arginine oxidation by A. stephensi NO synthase (AsNOS). Active TGF-beta1 persists in the mosquito midgut to extended times postingestion and is recognized by mosquito cells as a cytokine. In a manner analogous to the regulation of vertebrate inducible NO synthase and malaria parasite (Plasmodium) infection in mammals by TGF-beta1, TGF-beta1 regulates AsNOS expression and Plasmodium development in A. stephensi. Together, these observations indicate that, through conserved immunological cross talk, mammalian and mosquito immune systems interface with each other to influence the cycle of Plasmodium development.

Link between immune response and parasite synchronization in malaria

Anti-malaria vaccines and drugs could be greatly improved if we knew which phases of Plasmodium falciparum development in red blood cells are major inducers and which are major targets of natural immune responses. This information should focus attention on relevant immunogens and prove useful in developing immune-based therapies. Here we explore the hypothesis that innate immune responses mediate synchronization between the replication cycles of parasites in different red blood cells which is reflected in periodic fevers. Based on a recently developed, rather general mathematical model, we find that periodicity is highly sensitive to the position of both the inducing phase interval and the target phase interval in the parasite replication cycle. In addition, the degree of variability in the length of the replication cycle also strongly affects periodicity. To produce synchronization, the inducing and the target phase intervals must be developmentally distant from each other. We developed a computer program which prompts for information based on measurements of the numbers of erythrocytes in two replication cycle intervals chosen by the researcher, tests our model, and predicts the two phase intervals most critical to the synchronizing immune response. The program can be obtained from the authors.

Plasma levels of interleukin-18 and interleukin-12 in Plasmodium falciparum malaria

Interleukin (IL)-18 produced primarily by mononuclear phagocytes synergizes with IL-12 for interferon-gamma production from T, B and natural killer cells. It has been also demonstrated that, in Plasmodium falciparum malaria, IL-18 could have an immunoregulatory function. The aim of this study was to detect the plasma levels of IL-12 and IL-18, using an enzyme-linked immunosorbent assay, in 105 African children affected by mild and severe Plasmodium falciparum malaria to correlate the production of these cytokines with the severity of the disease. The levels of IL-18 and IL-12 were higher (25.7 +/- 7.6 pg/ml and 17.1 +/- 7.8 pg/ml, respectively) in children with mild malaria than in children with a severe form of the disease (21.5 +/- 10 pg/ml and 13.2 +/- 5.5 pg/ml, respectively). A positive correlation was observed between IL-18 and IL-12. This finding suggests that the production of these two cytokines (IL-18 and IL 12) may be coregulated and both have an immunoregulatory effect on the immune response in Plasmodium falciparum infection.

Secondary alveolar echinococcosis in lymphotoxin-alpha and tumour necrosis factor-alpha deficient mice: exacerbation of Echinococcus multilocularis larval growth is associated with cellular changes in the periparasitic granuloma

The availability of mice carrying a deletion of LT-alpha and tumour necrosis factor (TNF)-alpha genes enabled us to investigate the role of the TNF during alveolar echinococcosis. We compared the growth rate of Echinococcus multilocularis in LT-alphaTNF-alpha +/+ mice to that of mice having either no or only one LT-alphaTNF-alpha functionnal allele. LT-alphaTNF-alpha -/- mice harboured a significantly higher parasite burden than did the other two populations at 5, 10, and 15 weeks of infection, and they did not survive thereafter. Liver metacestodes removed from these mice were alive and the dehydrogenase activities of peritoneal metacestodes were decreased. Liver lesions regressed in most wild-type mice. Indeed, dead parasites were cordoned by granulomas containing numerous macrophages and lymphocytes leading to focal liver fibrosis at an early stage of infection. In contrast, most of LT-alphaTNF-alpha -/- mice harboured metacestodes interspersed with leucocytes, realising purulent abscesses with secondary extensive irregular fibrosis at a late stage of infection. Heterozygous mice had behavioural characteristics intermediate between homozygous mutants and wild-type mice. Levels of E. multilocularis-specific delayed-type hypersensitivity and serum antibodies were slightly decreased in LT-alphaTNF-alpha -/- mice. This study shows that TNF-alpha and/or LT-alpha genes play an essential role in the immune protection mechanisms against E. multilocularis at the site of infection.

gamma delta T-cells may interfere with a productive immune response in Plasmodium yoelii infections

Mice lacking alpha beta T-cells or gamma delta T-cells were infected with Plasmodium yoelii 17X NL (non-lethal) and followed for parasitaemia and cytokine production. While the parasitaemia in wild type mice resolved after reaching a peak value of 30 to 50%, it persisted in the -alpha beta T-cell mice until death. However, in the -gamma delta T-cell mice the peak parasitaemia was 12.5% of the levels seen in the wild type and -alpha beta T-cell mice and resolved faster than in the wild type mice. Higher levels of IL-10 and IFN-gamma were consistently found in the wild type and -gamma delta T-cell mice but not in the -alpha beta T-cell mice.