Microscopic and submicroscopic infection by Plasmodium falciparum: Immunoglobulin M and A profiles as markers of intensity and exposure

Assessment of serological Plasmodium falciparum–specific antibodies in highly endemic areas provides valuable information about malaria status and parasite exposure in the population. Although serological evidence of Plasmodium exposure is commonly determined by Plasmodium-specific immunoglobulin G (IgG) levels; IgM and IgA are likely markers of malaria status that remain relatively unexplored. Previous studies on IgM and IgA responses have been based on their affinity for single antigens with shortage of immune responses analysis against the whole Plasmodium proteome. Here, we provide evidence of how P. falciparum infection triggers the production of specific IgM and IgA in plasma and its relationship with parasite density and changes in hematological parameters. A total of 201 individuals attending a hospital in Breman Asikuma, Ghana, were recruited into this study. Total and P. falciparum–specific IgM, IgA, and IgG were assessed by ELISA and examined in relation to age (0–5, 14–49, and ≥50 age ranges); infection (submicroscopic vs. microscopic malaria); pregnancy and hematological parameters. Well-known IgG response was used as baseline control. P. falciparum–specific IgM and IgA levels increased in the population with the age, similarly to IgG. These data confirm that acquired humoral immunity develops by repeated infections through the years endorsing IgM and IgA as exposure markers in endemic malaria regions. High levels of specific IgA and IgM in children were associated with microscopic malaria and worse prognosis, because most of them showed severe anemia. This new finding shows that IgM and IgA may be used as diagnostic markers in this age group. We also found an extremely high prevalence of submicroscopic malaria (46.27% on average) accompanied by IgM and IgA levels indistinguishable from those of uninfected individuals. These data, together with the observed lack of sensitivity of rapid diagnostic tests (RDTs) compared to PCR, invoke the urgent need to implement diagnostic markers for submicroscopic malaria. Overall, this study opens the potential use of P. falciparum–specific IgM and IgA as new serological markers to predict malaria status in children and parasite exposure in endemic populations. The difficulties in finding markers of submicroscopic malaria are highlighted, emphasizing the need to explore this field in depth.

Plasmodium falciparum immunodominant IgG epitopes in subclinical malaria

Incomplete non-sterile immunity to malaria is attained in endemic regions after recurrent infections by a large percentage of the adult population, who carry the malaria parasite asymptomatically. Although blood-stage Plasmodium falciparum rapidly elicits IgG responses, the target antigens of partially protective and non-protective IgG antibodies as well as the basis for the acquisition of these antibodies remain largely unknown. We performed IgG-immunomics to screen for P. falciparum antigens and to identify epitopes associated with exposure and clinical disease. Sera from malaria cases identified five prevalent antigens recognized by all analyzed patients' IgGs. Epitope mapping of them, using adult and children sera samples from an endemic malaria region in Ghana segregated into patients with positive or negative subclinical detection of P. falciparum, revealed binding specificity for two 20-mer immunodominant antigenic regions within the START-related lipid transfer protein and the protein disulfide isomerase PDI8. These 20-mer epitopes challenged with sera samples from children under 5 years old displayed specific IgG binding in those with detectable parasitemia, even at subclinical level. These results suggest that humoral response against START and PDI8 antigens may be triggered at submicroscopic parasitemia levels in children and may eventually be used to differentially diagnose subclinical malaria in children.

Paediatric hospitalizations due to whooping cough in Spain (1997-2017)

This epidemiological survey estimates the burden of whooping cough in infants up to 12 months old in Spain during a twenty-one-year period (1997-2017). The survey was conducted by reviewing data from the Spanish Surveillance System for Hospital Data. All hospitalizations due to whooping cough for infants, reported during the 1997-2017 period, were analysed. Codes were selected from the International Classification of Diseases, 9th Revision, Clinical Modification diagnosis codes 033.0-033.9. To explore the latest national outbreak and the implementation of vaccination in pregnant women, analyses were stratified to compare the following periods: 1997-2010, 2011-2015 and 2016-2017. A total of 13,352 hospital discharges for whooping cough in infants up to 12 months old were reported. A total of 6850 discharges in the period 1997-2010, 5271 in the period 2011-2015 and 1231 in 2016-2017 were identified. The annual hospitalization rate prior to 2011 was 131.02 cases per 100,000 infants; in 2011-2015, the rate was significantly higher (250.13 cases per 100,000 infants) and in 2016-2017 it decreased (157.69 cases per 100,000 infants). Most of the cases (n = 11,446) occurred in infants under 4 months of age, with hospitalization rates of 328.80, 670.81 and 385.84 cases per 100,000 infants up to 4 months of age in the periods 1997-2010, 2011-2015 and 2016-17, respectively. Thirty-four deaths occurred in the period 1997-2010, 36 in the period 2011-2015 and 4 in 2016-2017. All of the deaths occurred in infants under 4 months old. The case fatality rate did not vary significantly across the study periods. Whooping cough infections concentrate in infants up to 4 months of age in Spain. Public health measures such as vaccination of pregnant women, caregivers, health care professionals and relatives, especially young parents, could reduce the hospitalization burden during the current outbreak.

Iron supplementation in mouse expands cellular innate defences in spleen and defers lethal malaria infection

The co-endemicity of malnutrition, erythrocytopathies, transmissible diseases and iron-deficiency contribute to the prevalence of chronic anaemia in many populations of the developing world. Although iron dietary supplementation is applied or recommended in at risk populations, its use is controversial due to undesirable outcomes, particularly regarding the response to infections, including highly prevalent malaria. We hypothesized that a boosted oxidative stress due to iron supplementation have a similar impact on malaria to that of hereditary anaemias, enhancing innate response and conditioning tissues to prevent damage during infection. Thus, we have analysed antioxidant and innate responses against lethal Plasmodium yoelii during the first five days of infection in an iron-supplemented mouse. This murine model showed high iron concentration in plasma with upregulated expression of hemoxygenase-1. The sustained homeostasis after this extrinsic iron conditioning, delayed parasitemia growth that, once installed, developed without anaemia. This protection was not conferred by the intrinsic iron overload of hereditary hemochromatosis. Upon iron-supplementation, a large increase of the macrophages/dendritic cells ratio and the antigen presenting cells was observed in the mouse spleen, independently of malaria infection. Complementary, malaria promoted the splenic B and T CD4 cells activation. Our results show that the iron supplementation in mice prepares host tissues for oxidative-stress and induces unspecific cellular immune responses, which could be seen as an advantage to promote early defences against malaria infection.

Respiratory Syncytial Virus Bronchiolitis in Children up to 5 Years of Age in Spain: Epidemiology and Comorbidities: An Observational Study

This epidemiological survey in Spain estimates the burden of respiratory syncytial virus (RSV) infection in children up to 5 year of age during a 15-year period (1997-2011). Observational retrospective survey was conducted by reviewing data of the National Surveillance System for Hospital Data, including >98% of Spanish hospitals. All hospitalizations related to RSV infection for children up to 5 years, reported during 1997-2011 period, were analyzed. Codes were selected by using the International Classification of Diseases 9th Clinical Modification 466.0-466.19, 480.1, and 079.6. A total of 326,175 and 286,007 hospital discharges for children up to 5 and 2 years of age were reported during the study period. The annual incidence was 1072 and 2413 patients per 100,000, respectively. The average length of hospital stay was 5.7 (standard deviation 8.2) days. Four hundred forty-six deaths were reported; of those, 403 occurred in children <2 years and 355 (80%) occurred in children <12 months of age. Hospitalization and mortality rates were significantly higher in boys and decrease significantly with age. The higher rate of hospitalization and mortality rates were found in the first year of life. Annual average cost for National Health Care System was € 47 M with a mean hospitalization cost of €2162. The average length of hospitalization and costs were significantly higher in high-risk children. RSV infections in children up to 5 year of age still pose a significant health threat in Spain, especially in the infants. The development of preventive, diagnostic, and therapeutic guidelines focused in children with comorbidities may help reduce the hospital and economic burden of the disease.

Early and late B cell immune responses in lethal and self-cured rodent malaria

ICR mice have heterogeneous susceptibility to lethal Plasmodium yoelii yoelii 17XL from the first days of experimental infection as evidenced by the different parasitemia levels and clinical outcomes. This mouse model has revealed specific immune responses on peripheral blood correlating with the infection fate of the animals. To search for immune-markers linked to parasitemia we examined B lymphocytes in organs of the immune system as key effectors of rodent immunity against malaria. To determine changes in immune cellularity fostered by the different prognostic parasitemia we examined B cell subsets in low (<15%) and high (>50%) parasitized mice during the first days of the infection. In the case of surviving mice, we studied the preservation of memory immune response 500 days after the primary P. yoelii challenge. Correlating with the parasitemia level, it was observed an increase in total cellularity of spleen during the first week of infection which remained after 16 months of the infection in surviving animals. B cell subsets were also modified across the different infection fates. Subpopulation as follicular B cells and B-1 cells proportions behaved differently depending on the parasitemia kinetics. In addition, peritoneal cavity cells proliferated in response to high parasitemia. More significantly, P. yoelii -specific memory B cells remained in the spleen 500 days after the primo-infection. This study demonstrates that B cell kinetics is influenced by the different parasitemia courses which are naturally developed within a same strain of untreated mice. We show that high levels of parasitemia at the beginning of infection promote an extremely fast and exacerbate response of several cell populations in spleen and peritoneal cavity that, in addition, do not follow the kinetics observed in peripheral blood. Furthermore, our results describe the longest persistence of memory B cells long time upon a single malaria infection in mice.

A comparison of two enzyme immunoassay tests for the detection of IgG antibodies for measles virus

BACKGROUND

Despite the reduction in the incidence of measles in recent years, outbreaks have appeared in various countries in Central and Western Europe. Estimating the percentage of immune individuals is fundamental for establishing control strategies in these situations.

METHODS

A total of 1,147 serum samples from healthy volunteers were tested by two commercial enzyme immunoassay (EIA) tests that detect antibodies for the measles virus: Enzygnost Anti-Measles Virus/IgG (Siemens, Marburg, Germany) and VIDAS Measles IgG (bioMerieux, Inc.). The following values were calculated for each test: sensitivity, specificity, positive and negative predictive values, and likelihood ratios.

RESULTS

Compared to the Enzygnost test, the sensitivity of the VIDAS test was 98.0% and the specificity was 78.1%. The likelihood ratio (LR) values were + 4.48, - 0.025 and +/- 0.17.

CONCLUSIONS

The VIDAS Measles IgG test is a quick method with good sensitivity for detecting IgG antibodies for the measles virus compared to the Enzygnost EIA test.

Differential immune response associated to malaria outcome is detectable in peripheral blood following Plasmodium yoelii infection in mice

Malaria infection in humans elicits a wide range of immune responses that can be detected in peripheral blood, but we lack detailed long-term follow-up data on the primary and subsequent infections that lead to naturally acquired immunity. Studies on antimalarial immune responses in mice have been based on models yielding homogenous infection profiles. Here, we present a mouse model in which a heterogeneous course of Plasmodium yoelii lethal malaria infection is produced in a non-congenic ICR strain to allow comparison among different immunological and clinical outcomes. Three different disease courses were observed ranging from a fatal outcome, either early or late, to a self-resolved infection that conferred long-term immunity against re-infection. Qualitative and quantitative changes produced in leukocyte subpopulations and cytokine profiles detected in peripheral blood during the first week of infection revealed that monocytes, dendritic cells and immature B cells were the main cell subsets present in highly-parasitized mice dying in the first week after infection. Besides, CD4(+)CD25(high) T cells expanded at an earlier time point in early deceased mice than in surviving mice and expressed higher levels of intracellular Foxp3 protein. In contrast, survivors showed a limited increase of cytokines release and stable circulating innate cells. From the second week of infection, mice that would die or survive showed similar immune profiles, although CD4(+)CD25(high) T cells number increased earlier in mice with the worst prognosis. In surviving mice the expansion of activated circulating T cell and switched-class B cells with a long-term protective humoral response from the second infection week is remarkable. Our results demonstrate that the follow-up studies of immunological blood parameters during a malaria infection can offer information about the course of the pathological process and the immune response.

Different vaccination strategies in Spain and its impact on severe varicella and zoster

Varicella vaccines available in Spain were marketed in 1998 and 2003 for non-routine use. Since 2006 some regions decided to include varicella vaccination in their regional routine vaccination programmes at 15-18 months of age. Other regions chose the strategy of vaccinating susceptible adolescents. This study shows the trends in severe varicella zoster virus infections through the analysis of the hospital discharges related to varicella and herpes zoster in the general population from 2005 to 2010 in Spain. A total of 11,125 hospital discharges related to varicella and 27,736 related to herpes zoster were reported during the study period. The overall annual rate of hospitalization was 4.14 cases per 100,000 for varicella and 10.33 cases per 100,000 for herpes zoster. In children younger than 5 years old varicella hospitalization rate significantly decreased from 46.77 in 2005 to 26.55 per 100,000 in 2010. The hospitalization rate related to herpes zoster slightly increased from 9.71 in 2005 to 10.90 per 100,000 in 2010. This increase was mainly due to the significant increase occurring in the >84 age group, from 69.55 to 97.68 per 100,000. When gathering for regions taking into account varicella vaccine strategy, varicella related hospitalizations decreased significantly more in those regions which included the vaccine at 15-18 months of age as a routine vaccine comparing with those vaccinating at 10-14 years old. No significant differences were found in herpes zoster hospitalization rates regarding the varicella vaccination strategy among regions. Severe varicella infections decreased after implementation of varicella vaccination in Spain. This decrease was significantly higher in regions including the vaccine at 15-18 months of age compared with those vaccinating susceptible adolescents.

Glutathione peroxidase contributes with heme oxygenase-1 to redox balance in mouse brain during the course of cerebral malaria

Oxidative stress has been attributed both a key pathogenic and rescuing role in cerebral malaria (CM). In a Plasmodium berghei ANKA murine model of CM, host redox signaling and functioning were examined during the course of neurological damage. Host antioxidant defenses were early altered at the transcriptional level indicated by the gradually diminished expression of superoxide dismutase-1 (sod-1), sod-2, sod-3 and catalase genes. During severe disease, this led to the dysfunctional activity of superoxide dismutase and catalase enzymes in damaged brain regions. Vitagene associated markers (heat shock protein 70 and thioredoxin-1) also showed a decaying expression pattern that paralleled reduced expression of the transcription factors Parkinson disease 7, Forkhead box O 3 and X-box binding protein 1 with a role in preserving brain redox status. However, the oxidative stress markers reactive oxygen/nitrogen species were not accumulated in the brains of CM mice and redox proteomics and immunohistochemistry failed to detect quantitative or qualitative differences in protein carbonylation. Thus, the loss of antioxidant capacity was compensated for in all cerebral regions by progressive upregulation of heme oxygenase-1, and in specific regions by early glutathione peroxidase-1 induction. This study shows for the first time a scenario of cooperative glutathione peroxidase and heme oxygenase-1 upregulation to suppress superoxide dismutase, catalase, heat shock protein-70 and thioredoxin-1 downregulation effects in experimental CM, counteracting oxidative damage and maintaining redox equilibrium. Our findings reconcile the apparent inconsistency between the lack of oxidative metabolite build up and reported protective effect of antioxidant therapy against CM.

Seroprevalence of antibodies against measles, rubella, mumps, varicella-zoster, and B. Pertussis in young adults of Madrid, Spain

In recent years, there has been an increase in the number of cases of certain immunopreventable diseases in our country. A high proportion of these have been recorded among the young adult population. The aim of this study was to determine the seroprevalence of antibodies against immunopreventable diseases with the greatest health impacts on the young adult population (19-39 y of age) in Madrid. We collected a total of 1,153 serum samples from healthy volunteers undergoing routine medical visits and used ELISA to determine the presence of IgG antibodies against measles, rubella, mumps, and varicella zoster, as well as Bordetella pertussis. The Pearson's χ(2) test was used to compare prevalences, the Mann-Whitney U test was used to compare means, and the Kruskal-Wallis test was applied for variables with more than 2 categories. Statistical significance was achieved with p values of<0.05. The global prevalence of antibodies was 92.1% for measles, 94.4% for rubella, 88.3% for mumps, 92.8% for varicella zoster, and 70.2% for B. pertussis. No statistically significant differences were found between genders. The prevalence of antibodies against measles was more than 95% in the group of individuals born after 1986, and the percentage of individuals susceptible to rubella was less than 5% in women born after 1986. In spite of adequate vaccination coverage, in our region, a population of young adults exists who have not achieved the objectives of the WHO for the elimination of measles and congenital rubella syndrome.

Insights into the preclinical treatment of blood-stage malaria by the antibiotic borrelidin

BACKGROUND AND PURPOSE

Blood-stage Plasmodium parasites cause morbidity and mortality from malaria. Parasite resistance to drugs makes development of new chemotherapies an urgency. Aminoacyl-tRNA synthetases have been validated as antimalarial drug targets. We explored long-term effects of borrelidin and mupirocin in lethal P. yoelii murine malaria.

EXPERIMENTAL APPROACH

Long-term (up to 340 days) immunological responses to borrelidin or mupirocin were measured after an initial 4 day suppressive test. Prophylaxis and cure were evaluated and the inhibitory effect on the parasites analysed.

KEY RESULTS

Borrelidin protected against lethal malaria at 0.25 mg·kg⁻¹·day⁻¹. Antimalarial activity of borrelidin correlated with accumulation of trophozoites in peripheral blood. All infected mice treated with borrelidin survived and subsequently developed immunity protecting them from re-infection on further challenges, 75 and 340 days after the initial infection. This long-term immunity in borrelidin-treated mice resulted in negligible parasitaemia after re-infections and marked increases in total serum levels of antiparasite IgGs with augmented avidity. Long-term memory IgGs mainly reacted against high and low molecular weight parasite antigens. Immunofluorescence microscopy showed that circulating IgGs bound predominantly to late intracellular stage parasites, mainly schizonts.

CONCLUSIONS AND IMPLICATIONS

Low borrelidin doses protected mice from lethal malaria infections and induced protective immune responses after treatment. Development of combination therapies with borrelidin and selective modifications of the borrelidin molecule to specifically inhibit plasmodial threonyl tRNA synthetase should improve therapeutic strategies for malaria.

Brain-derived neurotrophic factor and the course of experimental cerebral malaria

The role of neurotrophic factors on the integrity of the central nervous system (CNS) during cerebral malaria (CM) infection remains obscure, but the long-standing neurocognitive sequelae often observed in rescued children can be attributed in part to the modulation of neuronal survival and synaptic plasticity. To discriminate the contribution of key responses in the time-sequence of the pathogenic events that trigger the development of neurocognitive malaria syndrome we defined four stages (I-IV) of the neurological progression of CM in C57BL/6 mice infected with Plasmodium berghei ANKA. Upregulation of ICAM-1, VCAM-1, e-selectin and p-selectin expression was detected in all cerebral regions before parasitized red blood cells (pRBC) accumulation. As the severity of symptoms increased, BDNF mRNA progressively diminished in several brain regions, earliest in the thalamus-hypothalamus, cerebellum, brainstem and cortex, and correlated with a four-stage disease sequence. Immunohistochemical confocal microscopy revealed changes in the BDNF distribution pattern, suggesting altered axonal transport. During CM progression, molecular markers of neurological infection and inflammation in the parasite and the host, respectively, were accompanied by a switch in the brain constitutive proteasome to the immunoproteasome, which could impede normal protein turnover. In parallel with BDNF downregulation, NCAM expression also diminished with increased CM severity. Together, these data suggest that changes in BDNF availability could be involved in the pathogenesis of CM.

Parasitostatic effect of maslinic acid. II. Survival increase and immune protection in lethal Plasmodium yoelii-infected mice

Background

The anti-malarial activity of maslinic acid (MA), a natural triterpene which has been previously shown to exert a parasitostatic action on Plasmodium falciparum cultures, was analysed in vivo by using the Plasmodium yoelii 17XL murine model.

Methods

ICR mice were infected with P. yoelii and treated with a single dose of MA by a intraperitoneal injection of MA (40 mg kg^-1 day^-1) followed by identical dose administration for the following three days. Parasitaemia and accumulation of intraerythrocytic stages was monitored microscopically. To assess protective immunity, cured mice were challenged with the same dose of parasites 40 days after recovery from the primary infection and parasitaemia was further monitored for 30 days. Humoral response was tested by ELISA and visualization of specific anti-P. yoelii antibodies was performed by Western-blotting.

Results

ICR mice treated with MA increased the survival rate from 20% to 80%, showing an arrest of parasite maturation from day 3 to 7 after infection and leading to synchronization of the intraerythrocytic cycle and accumulation of schizonts by day 6, proving that MA also behaves as a parasitostatic agent in vivo. Mice which survived the primary infection displayed lower rates of parasitic growth, showing a decline of parasitaemia after day 15, and complete clearance at day 20. These mice remained immunoprotected, showing not malaria symptoms or detectable parasitaemia after rechallenge with the same lethal strain. The analysis of specific antibodies against P. yoelii, present in mice which survived the infection, showed a significant increase in the number and intensity of immunoreactive proteins, suggesting that the protected mice may trigger a strong humoral response.

Conclusion

The survival increase observed in MA-treated mice can be explained considering that the parasitostatic effect exerted by this compound during the first days of infection increases the chances to develop effective innate and/or acquired immune responses. MA may represent a new class of anti-malarial compounds which, as a consequence of its parasitostatic action, favours the development of more effective sterilizing immune responses.

Parasitostatic effect of maslinic acid. I. Growth arrest of Plasmodium falciparum intraerythrocytic stages

Background

Natural products have played an important role as leads for the development of new drugs against malaria. Recent studies have shown that maslinic acid (MA), a natural triterpene obtained from olive pomace, which displays multiple biological and antimicrobial activities, also exerts inhibitory effects on the development of some Apicomplexan, including Eimeria, Toxoplasma and Neospora. To ascertain if MA displays anti-malarial activity, the main objective of this study was to asses the effect of MA on Plasmodium falciparum-infected erythrocytes in vitro.

Methods

Synchronized P. falciparum-infected erythrocyte cultures were incubated under different conditions with MA, and compared to chloroquine and atovaquone treated cultures. The effects on parasite growth were determined by monitoring the parasitaemia and the accumulation of the different infective stages visualized in thin blood smears.

Results

MA inhibits the growth of P. falciparum Dd2 and 3D7 strains in infected erythrocytes in, dose-dependent manner, leading to the accumulation of immature forms at IC₅₀ concentrations, while higher doses produced non-viable parasite cells. MA-treated infected-erythrocyte cultures were compared to those treated with chloroquine or atovaquone, showing significant differences in the pattern of accumulation of parasitic stages. Transient MA treatment at different parasite stages showed that the compound targeted intra-erythrocytic processes from early-ring to schizont stage. These results indicate that MA has a parasitostatic effect, which does not inactivate permanently P. falciparum, as the removal of the compound allowed the infection to continue

Conclusions

MA displays anti-malarial activity at multiple intraerythrocytic stages of the parasite and, depending on the dose and incubation time, behaves as a plasmodial parasitostatic compound. This novel parasitostatic effect appears to be unrelated to previous mechanisms proposed for current anti-malarial drugs, and may be relevant to uncover new prospective plasmodial targets and opens novel possibilities of therapies associated to host immune response.

Haemoglobin interference and increased sensitivity of fluorimetric assays for quantification of low-parasitaemia Plasmodium infected erythrocytes

BACKGROUND

Improvements on malarial diagnostic methods are currently needed for the correct detection in low-density Plasmodium falciparum infections. Microfluorimetric DNA-based assays have been previously used for evaluation of anti-malarial drug efficacy on Plasmodium infected erythrocytes. Several factors affecting the sensitivity of these methods have been evaluated, and tested for the detection and quantification of the parasite in low parasitaemia conditions.

METHODS

Parasitaemia was assessed by measuring SYBRGreen I (SGI) and PicoGreen (PG) fluorescence of P. falciparum Dd2 cultures on human red blood cells. Different modifications of standard methods were tested to improve the detection sensitivity. Calculation of IC50 for chloroquine was used to validate the method.

RESULTS

Removal of haemoglobin from infected red-blood cells culture (IRBC) increased considerably the fluorescent signal obtained from both SGI and PG. Detergents used for cell lysis also showed to have an effect on the fluorescent signal. Upon depletion of haemoglobin and detergents the fluorescence emission of SGI and PG increased, respectively, 10- and 60-fold, extending notably the dynamic range of the assay. Under these conditions, a 20-fold higher PG vs. SGI fluorescent signal was observed. The estimated limits of detection and quantification for the PG haemoglobin/detergent-depleted method were 0.2% and 0.7% parasitaemia, respectively, which allow the detection of ~10 parasites per microliter. The method was validated on whole blood-infected samples, displaying similar results as those obtained using IRBC. Removal of white-blood cells prior to the assay allowed to increase the accuracy of the measurement, by reducing the relative uncertainty at the limit of detection from 0.5 to 0.1.

CONCLUSION

The use of PG microassays on detergent-free, haemoglobin-depleted samples appears as the best choice both for the detection of Plasmodium in low-density infections and anti-malarial drugs tests.

Altered nucleotide receptor expression in a murine model of cerebral malaria

In cerebral malaria, the most severe complication of malaria, both neurotransmission mechanisms and energy metabolism are affected. To understand how metabolic changes modify neurotransmission, we examined P2 receptor expression in a murine model of cerebral malaria. Quantitative polymerase chain reaction experiments revealed that parasite deposition was greatest in the cerebellum, compared with other areas of the brain, suggesting a correlation between brain parasitemia and loss of control of movement. Infected mice showed modified patterns of expression of P2 receptor subtype messenger RNA (mRNA), depending on both the specific purinergic receptor and the cerebral region analyzed. Immunohistochemical studies indicated altered levels of protein expression by these receptors in infected brains and, in some cases, a pattern of expression different from that noted in control mice. These differences in both the amount of mRNA and the protein distribution of P2 receptors observed in the different brain sites in infected mice suggest an important role for P2 receptors in either provoking cerebral damage or conferring neuroprotection.

Axodendritic fibres of mouse cerebellar granule neurons exhibit a diversity of functional P2X receptors

Distribution and functional expression of P2X receptors were analyzed in mouse cerebellum axodendritic fibres, using different experimental approaches such as RT-PCR, western blot, immunochemistry, microfluorimetric experiments and exocytotic studies. RT-PCR and western blot demonstrated the presence of P2X1-4,7 subunits in both whole cerebellum and mouse cerebellar granule cultured neurons. Immunochemistry analysis of tissular and cellular location of P2X1-4,7 receptors confirmed their presence and unequal distribution between somas and axodendritic prolongations. Microfluorimetric experiments using a variety of modulators of the P2X subunits revealed the presence of different functional P2X receptors in the axodendritic fibres. The use of the synthetic agonist alpha,beta-meATP and the antagonist Ip(5)I revealed the activation of functional P2X1 and P2X3 receptors. Responses mediated by P2X1 subunits were also confirmed by using ZnSO(4). Activation of functional P2X4 receptors is observed when stimulated in the presence of ivermectin. Exocytotic studies confirmed the role of most P2X subunits in the activation of neurotransmitter release in axodendritic fibres from mouse cerebellar granule neurons.

Glutamate release and synapsin-I phosphorylation induced by P2X7 receptors activation in cerebellar granule neurons

The present work reports that activation of P2X7 receptor induces synaptic vesicle release in granule neurons and phosphorylation of synapsin-I by calcium-calmodulin-dependent protein kinase II (CaMKII), which in turn modulates secretory event. ATP, in absence of magnesium, induced a concentration-dependent glutamate release with an EC50 value of 1.95 microM. The involvement of P2X7 receptor was suggested when maximal secretory response was significantly reduced by the selective P2X7 antagonist Brilliant Blue G (BBG; 100 nM) and abolished by removing extracellular Ca2+. The involvement of P2X7 receptor on synaptic vesicle release was confirmed by measuring the release of FM 1-43 dye. In this case, pharmacological activation of P2X7 was achieved with the more selective agonist 2'-3'-o-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP; 100 microM) showing a significant FM 1-43 release that was blocked by BBG (100 nM), by Zn2+ ions (100 microM), both P2X7 blockers, but not by suramin (100 microM), antagonist of P2X1, P2X2, P2X3 and P2X5. In addition, BzATP, through P2X7 receptor activation, significantly increased the phosphorylation of synapsin-I, the main presynaptic target of CaMKII. Both effects mediated by BzATP were inhibited by the CaMKII inhibitors KN-62 (10 microM) and KN-93 (10 microM). These results suggest, therefore, that Ca2+ entrance mediated by P2X7 receptor induces glutamate release and in parallel synapsin-I phosphorylation.

Existence of high and low affinity dinucleotides pentaphosphate-induced calcium responses in individual synaptic terminals and lack of correlation with the distribution of P2X1-7 subunits

Individual analysis of synaptic terminals calcium responses, induced by dinucleotides pentaphosphate, Ap(5)A or Gp(5)G, demonstrates the presence of two main groups considering the concentration required for stimulation. The first group corresponds to those responding to Ap(5)A or Gp(5)G at nanomolar concentration, representing 16% and 12%, respectively, and the second one responds to micromolar concentration and represents, respectively, 17% and 14%, of the total functional synaptosomal population in rat midbrain. Dose-response curves in single terminals showed an Ap(5)A EC(50) values of 0.9+/-0.2 nM and 11.8+/-0.9 microM, being the maximal intrasynaptosomal calcium increase of 200+/-0.3 and 125+/-0.2 nM for the high and low affinity responding terminals, respectively. Combination of microfluorimetric and immunocytochemical studies showed lack of correlation between dinucleotides pentaphosphate responses and P2X receptor subunits expression, in spite of the abundance of P2X(2), P2X(3) and P2X(7) at the presynaptic level in rat midbrain synaptosomes. Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a P2X receptors antagonist, showed no effect on low affinity dinucleotides receptors population, and partial inhibition on the high affinity one. On the other hand, diinosine pentaphosphate (Ip(5)I) completely abolished the low affinity dinucleotides responses, and 60% inhibition of the high affinity ones.

Characterization of a functional P2X7-like receptor in cerebellar granule neurons from P2X7knockout mice

The presence of ionotropic P2X(7) receptor has been studied in mice brain from wild type and P2X(7) receptor knockout animals. Western blot and immunocytochemical assays show the presence of a protein containing the P2X(7) immunogenic epitopes in the brain of knockout model. Reverse transcriptase polymerase chain reaction experiments demonstrate the absence of the disrupted sequence, but other sequences of P2X(7) specific mRNA expression have been detected. Functional calcium imaging experiments in cultured granule neurons from P2X(7) knockout cerebella show the existence of a functional P2X(7)-like receptor that keeps some of the properties of the genuine receptor.

Stereological Study of the External Urethral Sphincter in the Female Urethra of the Lamb: A New Model for Studies on Urinary Continence

Some of the morphometrical features and functional properties of the lamb external urethral sphincter (EUS) were determined by means of ATPase histochemistry. In this study, eight female urethras of 2- to 3-month-old lambs were used. The samples were studied by using an unbiased stereological design and were statistically evaluated with a Kolmogorov-Smirnov test. Additionally, the mechanical activity of the different fibre types was analysed by measuring the isometric changes in tension induced by electrical field stimulation (EFS) of intrinsic nerves. The lamb EUS has an average fibre density of 1142.37 fibres/mm(2) (SD = 279.33). Our data showed the predominance of fast-twitch fibres or type II fibres, with a proportion of 30% (type I) and 70% (type II) in all cases. These percentages remained the same along the length of the EUS. However, a clear tendency to increase the number of both fibre types in the mid-EUS was observed. Interestingly, type I and II fibres are intermingled throughout the whole lamb EUS. Dynamic parameters of the contraction induced in lamb EUS preparations by EFS of intramural nerves, were intermediate between fast- and slow-twitch muscles. Furthermore, contractile activity showed no decrease in amplitude upon repetitive stimulation, suggesting the presence of a mixture of fibre types, in which fast but fatigue-resistant fibres (probably type IIA) seem to predominate. Our results indicate that lambs could be suggested as a new biological model to study those pathological processes, which involve the sphincteric regulation of the EUS.

Mutational analysis ofBRCA1andBRCA2in Mediterranean Spanish women with early-onset breast cancer: Identification of three novel pathogenic mutations

In Spain, the contribution of BRCA mutations to the population incidence of early-onset breast cancer was unknown. We carried out a mutational analysis of the BRCA1 and BRCA2 genes in 124 Spanish women diagnosed with breast cancer before the age 41 and who were not selected for a family history of this disease. The genetic study was performed by PCR-SSCP analysis and DNA sequencing. We identified 6 pathogenic BRCA mutations in 7 unrelated probands (5.6%; 95% CI=2.3% to 11.3%): 1 BRCA1 (c.2080delA) and 5 BRCA2 (p.Y3006X, p.Q1994X, c.9204_9217del14, c.9254_9258del5 and c.295+2T>C). Three out of 6 mutations were novel (BRCA2 p.Y3006X, c.9204_9217del14, and c.295+2T>C), and two further mutations had not been previously found in Spain (BRCA1 c.2080delA and BRCA2 p.Q1994X). The one remaining (BRCA2 c.9254_9258del5) was detected in two probands of our sample. Additionally, we identified two new missense mutations: BRCA1 p.P1812A and BRCA2 p.G2044A. Our data support the notion that Spaniards represent a heterogeneous population with its own spectrum of BRCA mutations, some of which appear as founding mutations. We categorized patients into familial or non-familial groups on the basis of her family history of breast/ovarian cancer; this analysis indicated that among Spanish women with early-onset breast cancer, an even moderate family history is a good predictor of being a BRCA mutation carrier.

Neurochemical heterogeneity of the thalamic reticular and perireticular nuclei in developing rabbits: patterns of calbindin expression

The thalamic reticular nucleus (TRN) forms an essential part of the circuits that link the thalamus to the cortex, whereas the perireticular thalamic nucleus (PRN) consists of scattered neurons that are located in the internal capsule, in close relation to the TRN. A common feature of these nuclei in different species is the immunoreactivity for some calcium binding proteins with a developmental pattern of expression. In the present study, sections from rabbits at different ages were examined to determine the calbindin (CB) expression in the developing TRN and PRN at the first stages of development. These CB-expressing cells constitute an important subpopulation of neurons in the caudal half of the developing TRN. In the adult, there are still positive CB somata in the middle and caudal halves of the nucleus. In the PRN, where the developmental pattern of CB expression has not been described before, the number of CB perireticular cells decreases progressively. Our results, together with previous data in the rabbit suggest the existence of remarkable neurochemical heterogeneity in the TRN and PRN of the rabbit.

Molecular genetics of familial hypercholesterolemia in Spain: Ten novel LDLR mutations and population analysis

Mutations underlying FH in Spain are largely unknown because only a few and limited surveys have been carried out on Spanish FH patients up to now. To gain information on this issue, we have analysed a group of 113 unrelated Spanish FH patients from an eastern area of Spain (Valencian Community). We have screened the LDLR gene by Southern blot and PCR-SSCP analysis to detect large rearrangements and small mutations, respectively. In addition, we have screened the Apo B gene for mutations known to cause FDB by PCR-SSCP analysis. We have identified a total of 47 different mutations in the LDLR gene (5 large rearrangements, and 42 small mutations, which were characterized by DNA sequencing), 19 of which have not been described in other populations (Valencia-1 to -4, 112insA, P160R, 790DelATGA, 920insTCAG, G642E, and the ten novel mutations E246A, 884delT, I289T, S305F, Q328X, Y354C, I603del, 2312-3C>A, V779M, and N804K). Three of these mutations (15%) were present in more than 1 proband, being mutation 112insA the most prevalent (frequency approximately 8%) in our sample. The Apo B gene R3500Q mutation was found in only one patient and no underlying defect was found in about 27% of patients. Our data support the notion that Spaniards represent a heterogeneous population with its own spectrum of LDLR gene mutations and that, in our population, FDB has a lower frequency or a milder expression than in central Europe countries.

Spinal cord central canal of the German shepherd dog: morphological, histological, and ultrastructural considerations

This study deals with some macroscopical, microscopical, and ultrastructural aspects of the spinal cord central canal of the German shepherd dog. The caudal end of the spinal cord is constituted by the conus medullaris, which may extend to the first sacral vertebra, the terminal ventricle, and the filum terminale. The latter structure is considered as internum (second to third sacral vertebrae) or externum (fifth caudal vertebra), according to its relation to the dura mater. Occasionally, there is a second anchorage which is close to the level of the sixth caudal vertebra. The central canal is surrounded by a ciliated ependymal epithelium, which differs depending upon the levels. The most caudal part of the filum terminale bears a columnar ciliated ependymal epithelium surrounded by two layers of glia and pia mater, which separate the central canal from the subarachnoid space. Microfil injections show a communication between the cavity and the subarachnoid space, as the plastic is able to pass through the ependymal epithelium. At the level of the terminal ventricle there are real separations of the ependymal epithelium, which seem to connect the lumen of the spinal canal with the subarachnoid space. These structures probably constitute one of the drainage pathways of the cerebrospinal fluid. The diameter of the central canal is related to the age of the animal. However, even in very old animals the spinal cord central canal reaches the tip of the filum terminale and remains patent until death. At the ultrastructural level the ependymal cells present villi, located on cytoplasmic projections, cilia, dense mitochondria, and oval nuclei.