Dynamics of PfEMP1 Antibody Profile From Birth to 12 Months of Age in Beninese Infants

BACKGROUND

Plasmodium falciparum-infected erythrocytes bind to specific endothelial cell receptors via members of the PfEMP1 family exported onto the erythrocyte surface. These interactions are mediated by different types of cysteine-rich interdomain region (CIDR) domains found in the N-terminal region of all PfEMP1. CIDRα1 domains bind endothelial protein C receptor (EPCR), CIDRα2-6 domains bind CD36, whereas the receptor specificity of CIDRβ/γ/δ domains is unknown.

METHODS

In this study, we investigated the level of immunoglobulin (Ig)G targeting the different types of PfEMP1 CIDR during the first year of life. We used plasma collected longitudinally from children of pregnant women who had been followed closely through pregnancy.

RESULTS

Antibodies to CIDRα1 domains were more frequent in cord blood compared with antibodies to CIDRα2-6 domains. Higher IgG levels to EPCR-binding CIDRα1 variants positively correlated with the timing of first infections. Antibodies to all PfEMP1 types declined at similar rates to the point of disappearance over the first 6 months of life. At 12 months, children had acquired antibody to all types of CIDR domains, mostly in children with documented P falciparum infections.

CONCLUSIONS

These observations agree with the notion that the timing and phenotype of first P falciparum infections in life are influenced by the immune status of the mother.

Measuring Lactase Enzymatic Activity in the Teaching Lab

Understanding how enzymes work, and relating this to real life examples, is critical to a wide range of undergraduate degrees in the biological and biomedical sciences. This easy to follow protocol was developed for first year undergraduate pharmacy students and provides an entry-level introduction to enzyme reactions and analytical procedures for enzyme analysis. The enzyme of choice is lactase, as this represents an example of a commercially available enzyme relevant to human disease/pharmaceutical practice. Lactase is extracted from dietary supplement tablets, and assessed using a colorimetric assay based upon hydrolysis of an artificial substrate for lactase (ortho-nitrophenol-beta-D-galactopyranoside, ONPG). Release of ortho-nitrophenol following the hydrolytic cleavage of ONPG by lactase is measured by a change in absorbance at 420 nm, and the effect of the temperature on the enzymatic reaction is evaluated by carrying out the reaction on ice, at room temperature and at 37 °C. More advanced analysis can be implemented using this protocol by assessing the enzyme activity under different conditions and using different reagents.

Determinants of primary healthcare seeking behaviours for children during the first 18 months of life in Benin

Background

Primary healthcare is a key element of management of childhood illness in Africa. The objectives were to identify primary care seeking determinants among infants and young children up to 18 mo in a birth cohort from Benin.

Methods

From 2007 to 2009 in Benin, a birth cohort was followed until the age of 18 mo in three health centres. Multilevel Poisson regression models were fitted to identify the factors related to the monthly number of consultations. Maternal and newborn characteristics and infant general health parameters were considered.

Results

A total of 566 children were followed. On average, 0.46 consultations per month per child were recorded. The number of consultations was significantly lower after the first 6 mo of life (p<0.001). A distance >1000 m was associated with fewer consultations (p=0.01). Primiparity was significantly associated with higher care seeking (relative risk 1.17 [95% CI 1.05 to 1.30], p<0.01). No child characteristics at birth were significantly associated with the number of consultations (all p>0.16).

Conclusions

Development of health structures and improvement of access remain important goals for strengthening of the primary care health system. Studying factors of care seeking behaviour, like parity, can help to identify women more prone to seek care for their child during the first year of life.

[Multiple imputation of missing at random data: General points and presentation of a Monte-Carlo method]

BACKGROUND

Statistical analysis of a data set with missing data is a frequent problem to deal with in epidemiology. Methods are available to manage incomplete observations, avoiding biased estimates and improving their precision, compared to more traditional methods, such as the analysis of the sub-sample of complete observations.

METHODS

One of these approaches is multiple imputation, which consists in imputing successively several values for each missing data item. Several completed data sets having the same distribution characteristics as the observed data (variability and correlations) are thus generated. Standard analyses are done separately on each completed dataset then combined to obtain a global result. In this paper, we discuss the various assumptions made on the origin of missing data (at random or not), and we present in a pragmatic way the process of multiple imputation. A recent method, Multiple Imputation by Chained Equations (MICE), based on a Monte-Carlo Markov Chain algorithm under missing at random data (MAR) hypothesis, is described. An illustrative example of the MICE method is detailed for the analysis of the relation between a dichotomous variable and two covariates presenting MAR data with no particular structure, through multivariate logistic regression.

RESULTS

Compared with the original dataset without missing data, the results show a substantial improvement of the regression coefficient estimates with the MICE method, relatively to those obtained on the dataset with complete observations.

CONCLUSION

This method does not require any direct assumption on joint distribution of the variables and it is presently implemented in standard statistical software (Splus, Stata). It can be used for multiple imputation of missing data of several variables with no particular structure.

Role for protease activity in visceral pain in irritable bowel syndrome

Mediators involved in the generation of symptoms in patients with irritable bowel syndrome (IBS) are poorly understood. Here we show that colonic biopsy samples from IBS patients release increased levels of proteolytic activity (arginine cleavage) compared to asymptomatic controls. This was dependent on the activation of NF-kappaB. In addition, increased proteolytic activity was measured in vivo, in colonic washes from IBS compared with control patients. Trypsin and tryptase expression and release were increased in colonic biopsies from IBS patients compared with control subjects. Biopsies from IBS patients (but not controls) released mediators that sensitized murine sensory neurons in culture. Sensitization was prevented by a serine protease inhibitor and was absent in neurons lacking functional protease-activated receptor-2 (PAR2). Supernatants from colonic biopsies of IBS patients, but not controls, also caused somatic and visceral hyperalgesia and allodynia in mice, when administered into the colon. These pronociceptive effects were inhibited by serine protease inhibitors and a PAR2 antagonist and were absent in PAR2-deficient mice. Our study establishes that proteases are released in IBS and that they can directly stimulate sensory neurons and generate hypersensitivity symptoms through the activation of PAR2.

Dynamics of anti-VAR2CSA immunoglobulin G response in a cohort of senegalese pregnant women

BACKGROUND

Pregnancy-associated malaria (PAM) is precipitated by the accumulation of parasites in the placental intervillous spaces and causes maternal anemia and low birth weight. In PAM, placental parasites adhere to chondroitin sulfate A (CSA) through a unique set of variant surface antigens (VSAPAM). Several studies have shown that 1 var gene, var2csa, is transcribed at high levels and expressed in CSA-binding Plasmodium falciparum parasites.

METHODS

Plasma levels of anti-VAR2CSA immunoglobulin G (IgG) in Senegalese women were measured during pregnancy by enzyme-linked immunosorbent assay, using 3 recombinant proteins representing 3 domains of the var2csa gene product.

RESULTS

The 3 recombinant proteins were specifically recognized by plasma from pregnant women but not by control plasma. A parity-dependent recognition pattern was observed with 2 of the 3 VAR2CSA antigens. A kinetic study demonstrated that a single P. falciparum infection was able to trigger a VAR2CSA-specific antibody response. Among women with infected placentas, women with high anti-VAR2CSA IgG levels at enrollment were more likely to present with a past infection than with an acute/chronic infection.

CONCLUSIONS

Anti-VAR2CSA IgGs are involved in clinical protection against pregnancy-associated malaria and strengthens the hope for making a VAR2CSA-based vaccine.

Mast cell tryptase and proteinase-activated receptor 2 induce hyperexcitability of guinea-pig submucosal neurons

Mast cells that are in close proximity to autonomic and enteric nerves release several mediators that cause neuronal hyperexcitability. This study examined whether mast cell tryptase evokes acute and long-term hyperexcitability in submucosal neurons from the guinea-pig ileum by activating proteinase-activated receptor 2 (PAR2) on these neurons. We detected the expression of PAR2 in the submucosal plexus using RT-PCR. Most submucosal neurons displayed PAR2 immunoreactivity, including those colocalizing VIP. Brief (minutes) application of selective PAR2 agonists, including trypsin, the activating peptide SL-NH2 and mast cell tryptase, evoked depolarizations of the submucosal neurons, as measured with intracellular recording techniques. The membrane potential returned to resting values following washout of agonists, but most neurons were hyperexcitable for the duration of recordings (> 30 min-hours) and exhibited an increased input resistance and amplitude of fast EPSPs. Trypsin, in the presence of soybean trypsin inhibitor, and the reverse sequence of the activating peptide (LR-NH2) had no effect on neuronal membrane potential or long-term excitability. Degranulation of mast cells in the presence of antagonists of established excitatory mast cell mediators (histamine, 5-HT, prostaglandins) also caused depolarization, and following washout of antigen, long-term excitation was observed. Mast cell degranulation resulted in the release of proteases, which desensitized neurons to other agonists of PAR2. Our results suggest that proteases from degranulated mast cells cleave PAR2 on submucosal neurons to cause acute and long-term hyperexcitability. This signalling pathway between immune cells and neurons is a previously unrecognized mechanism that could contribute to chronic alterations in visceral function.

Kainic acid-induced generalized seizures alter the regional hippocampal expression of the rat m1 and m3 muscarinic acetylcholine receptor genes

We investigated the gene expression responses using in situ hybridization with radiolabelled riboprobes for the m1 and m3 subtypes of muscarinic cholinergic receptors in the rat hippocampus following a brief (5-min) kainic acid-induced behavioral seizure. The kainic acid was intraperitoneally administered, and the ensuing generalized convulsive seizure terminated with diazepam. Our results demonstrate that the expression of the m1 subtype was significantly reduced in the CA1, CA3 and the dentate granule cells by 3 h after the administration of kainic acid while no significant change was observed in any hippocampal subfield for the m3 subtype. By 6 h post challenge, the m1 subtype was still decreased in all hippocampal subfields examined, while the m3 subtype remained unchanged from vehicle injected control. At 24 h post challenge, both the m1 and m3 subtypes were significantly reduced in the CA1 and CA3 subfields; the expression of the m1 subtype in the dentate granule cells, however, had recovered to levels indistinguishable from vehicle-injected control. These results demonstrate that epileptiform activity induced by kainic acid administration promotes alterations in the expression levels for both the m1 and m3 muscarinic receptor genes, and suggest that the activity of this neuromodulatory system in the hippocampus may be altered through activity-dependent mechanisms at early times following seizures.

Auditory-evoked response morphology in profoundly-involved multi-handicapped children: comparisons with normal infants and children

The developmental and difference/defect theories have been used to explain auditory development in some multi-handicapped children. If developmental factors influence auditory response behaviors, it might be predicted that evoked potentials measured from the central auditory nervous system would reflect similar developmental influences in multi-handicapped children. The purpose of this study was to compare auditory-evoked-potential waveform morphology between profoundly-involved multi-handicapped children and normal infants and children. Auditory brainstem response (ABR) and middle-latency response (MLR) morphology were examined from waveform descriptions, wave detection, latency, amplitude, and spectral energy measures. The majority of handicapped subjects exhibited response morphology unlike that of normal children or infants. ABR/MLR morphology for handicapped children was characterized by depressed responses and substantial waveform variability. The results of this study tended to support the difference/defect theory.

Decreased voluntary ethanol selection in amygdala-kindled rats

Kindled and control rats were exposed to either ethanol or dextrose solutions in the limited access paradigm, a paradigm that allows access to the test solution for only 1 h each day. Limited access trials were initiated either 24 h or 30 days after the fifth stage 5 seizure had been elicited in the kindled subjects. As previously reported, increased voluntary ethanol selection was observed in the limited access paradigm. Kindled subjects, however, ingested significantly less ethanol than controls. This difference was found both when limited access trials were started 24 h after the last seizure and when they were started 30 days after the last seizure. Kindled and control subjects did not differ in their intake of dextrose solutions.