Longitudinal study of Plasmodium falciparum infection and immune responses in infants with or without the sickle cell trait.

BACKGROUND: Individuals may be homozygous (SS) or heterozygous (AS) sickle cell gene carriers or have normal adult haemoglobin (AA). Haemoglobin S could have a protective role against malaria but evidence is sparse and the operating mechanisms are poorly known. METHODS: We followed two cohorts of children. The first was enrolled at birth (156 newborn babies) and the second at 24-36 months old (84 children). Both cohorts were followed for 30 months; monthly for parasitological data and half yearly for immunological data. RESULTS: In the first cohort, 22%, and in the second 13% of children were AS. Whatever their age parasite prevalence rates were similar in AA and AS individuals. Mean parasite densities increased less rapidly with age in AS than in AA children, and were significantly lower in AS than in AA children >48 months old. The AA children tended to be more often admitted to hospital than AS children (22% versus 11%, NS). Both anti-Plasmodium falciparum and anti-Pfl55/RESA antibody rates increased more rapidly in AA than in AS children. Conversely, the prevalence rate of cellular responders to the Pfl55/RESA antigen was similar in AA and AS children during the first 2 years of life, then it was higher in AS than in AA children. CONCLUSIONS: Sickle cell trait related antimalarial protection varies with age. The role of the modifications of the specific immune response to P. falciparum in explaining the protection of AS children against malaria is discussed.

Prevalence of and risk factors for anemia in young children in southern Cameroon.

Anemia during childhood remains a major public health challenge in sub-Saharan Africa. To determine the prevalence of and the main risk factors for anemia in young children, we conducted a longitudinal survey in Ebolowa in southern Cameroon. Children were enrolled in two cohorts and followed during a three-year period: the first cohort was composed of 122 children from 0 to 36 months of age and the second cohort was composed of 84 children from 24 to 60 months of age. The two cohorts were followed weekly for symptomatic malaria, monthly for both symptomatic and asymptomatic malaria, and every six months for hematologic data; the children were grouped into six-month age groups. The prevalence of anemia (hemoglobin [Hb] level < 11 g/dl) was the highest in the six-month-old age group (47%) and the age-related evolution clearly showed a decrease in the prevalence from three years of age. Thus, 42% of the children less than three years of age were anemic, while 21% of the children between three and five years of age were anemic. The lowest mean +/- SD Hb content (10.7 +/- 2.1 g/dl) was observed in the six-month-old children and a regular improvement in the Hb level occurred from six months to three years of age. A stabilization was observed at a level of approximately 12 g/dl. At any age, there was no difference in mean Hb levels between children with AS and AA Hb genotypes. Hookworm infection was diagnosed in two children in the study population. Results of a multivariate analysis showed that placental malaria infection was the strongest risk factor for anemia in the six-month-old children (odds ratio [OR] = 3.6; 95% confidence interval [CI] = 1.1-12.3) and was independent of the frequency of parasitemia, parasitemia at the time of Hb measurement, or microcytosis. In the one-year-old age group, microcytosis was a significant factor related to anemia (OR = 2.8, 95% CI = 1-7.8) pointing out the role of iron deficiency at this age. Parasitemia at the time of Hb measurement was significantly associated with anemia in all age groups (except in 54- and 60-month-old groups). Strategies to decrease the prevalence of anemia in young children in southern Cameroon should include chemoprophylaxis for pregnant women, prevention of acquired malaria infection in both pregnancy and infancy, and prevention of nutritional iron deficiency.

Maternal placental infection with Plasmodium falciparum and malaria morbidity during the first 2 years of life.

In areas endemic for malaria, pregnant women frequently present with a placenta that has been parasitized by Plasmodium falciparum, an infection associated with a reduction in the birth weight of the offspring. However, the impact of placental infection on malaria-related morbidity during the infant's first years of life has not been investigated. Between 1993 and 1995, 197 children in southern Cameroon were followed weekly clinically and monthly parasitologically. The dates of first positive blood smear and the evolution of the parasite prevalence rates were compared between infants born to mothers presenting with (n = 42) and without (n = 155) P. falciparum infection of the placenta. Infants born to placenta-infected mothers were more likely to develop a malaria infection between 4 and 6 months of age; then the difference progressively disappeared. Similarly, parasite prevalence rates were higher in placenta-infected infants from 5 to 8 months of age. Thus, malarial infection of the placenta seems to result in a higher susceptibility of infants to the parasite. This was not related to maternally transmitted antibodies, as specific antibody levels were similar in both groups of infants. A better understanding of the involved mechanisms may have important implications for the development of malaria control strategies.

PIP: Parasitization of the placenta with Plasmodium falciparum is not uncommon in pregnant women in areas endemic for malaria and has been associated with low birth weight. To assess the impact of placental infection on malaria-related morbidity during the first 2 years of life, 197 children from southern Cameroon were followed weekly clinically and monthly parasitologically in 1993-95. 42 infants (21.3) had mothers with P. falciparum placental infection. Umbilical cord blood levels of total and specific anti-P. falciparum immunoglobulin were similar in both groups of infants. Infants born to placenta-infected mothers were significantly more likely to develop malaria at 4-6 months of age--but not in subsequent months--than those born to non-placenta-infected mothers. Similarly, parasite prevalence rates were higher in placenta-infected infants from 5-8 months of age. 46.5% of children in the placenta-infected mother group and 38.5% of those in the non-placenta-infected mother group had at least one malaria attack during the study period. These findings indicate that infants of mothers presenting with P. falciparum infection of the placenta are more susceptible to malaria infection in the first 2 years of life. Improved understanding of the mechanisms underlying immune responses to P. falciparum in newborns and infants is needed to guide the development of malaria control strategies.

Comparative performances of six agglutination kits assessed by using typical and atypical strains of Staphylococcus aureus.

Six commercial agglutination tests designed for the identification of Staphylococcus aureus were compared by using a strain collection which included 512 staphylococci representing 33 species (318 isolates of Staphylococcus aureus [including 144 oxacillin resistant], 46 S. epidermidis isolates, 15 S. haemolyticus isolates, 12 S. saprophyticus isolates, 29 S. schleiferi isolates, 30 S. lugdunensis isolates, and 62 other coagulase-negative staphylococci). This group also included a proportion of strains with unusual phenotypes (e.g., 19 coagulase-negative S. aureus isolates, 26 clumping factor-negative S. aureus isolates, and 4 S. aureus isolates each with a double deficiency). The overall sensitivity for identification of typical and atypical S. aureus was high with the Staphaurex Plus test (Murex Biotech) (99.7%), the Pastorex Staph Plus test (Sanofi Diagnostics Pasteur) (99.7%), and the Slidex Staph Plus test (bioMérieux) (100%). The overall rate of specificity was affected by the unusual inclusion in this study of a high proportion of non-S. aureus species, such as S. lugdunensis and S. schleiferi, which express a clumping factor and therefore produce a positive result with the agglutination tests.

Kinetic, computer, and electron microscopic studies dealing with an artificial enzyme membrane: theoretical and experimental evaluation of the cytochemical demonstration of acetylcholinesterase.

The cytochemical demonstration of acetylcholinesterase is theoretically and experimentally evaluated with a model system. The model is an artificial proteic membrane in which acetylcholinesterase homogeneously is immobilized chemically by a bifunctional agent, glutaraldehyde. The copper-thiocholine histochemical method is studied kinetically and the system is simulated by computer calculations based on experimental kinetic parameters and numerical analysis methods. In addition, the corresponding electron micrographs are presented. These studies lead to the conclusions that the system is ruled by diffusional constraints and that enzyme distribution and repartition of the insoluble electron dense product are not circumscribed by any specific conditions.

Effects of high calcium solutions on glutamate sensitivity of crayfish muscle fibres.

Crayfish neuromuscular preparations were studied after 18--36 h exposure to high calcium solutions. As previously reported for frog neuromuscular preparations the treatment damaged the nerve terminals and decreased junctional potentials. The resting potentials and input resistances of the muscle fibres were not affected; but their sensitivity to glutamate was significantly decreased when compared to that of control muscles. After exposure to high calcium, the sensitivity to gamma-aminobutyric acid, the putative transmitter at inhibitory synapses, was increased. Apparently normal twitches were elicited by direct stimulation, and calcium spikes could still be observed in the fibres. A decreased sensitivity to glutamate was also noted in experiments carried out on denervated muscles 8 months after section of the motor axons. Possible relations between nerve terminal damage and the decrease in sensitivity to glutamate are discussed.

A histochemical model dealing with an immobilized glucose oxidase-peroxidase system. The influence of diffusion limitations on histochemical results.

A histochemical model dealing with an immobilized bienzyme system (glucose oxidase-peroxidase) is presented. The model is an artificial proteic membrane obtained by a previously described co-cross-linking process. The kinetic properties of free and immobilized horseradish peroxidase were studied when 3,3'-diaminobenzidine is used as a hydrogen donor substrate. A new direct method was developed for immobilized enzyme activity measurements. Computer simulation based on experimental kinetic parameters was performed in order to discuss electron microscopy results. By changing diffusion limitations, various profiles of insoluble product were visualized inside the proteic film and no geometrical similarity was seen between enzyme distributions and insoluble osmiophilic product patterns.

Theoretical and experimental study of an immobilized bienzyme system. Computer calculations and electron microscopy visualization of local concentration profiles.

A cytochemical method was used in order to visualize the existence of local concentrations of metabolites within an immobilized bienzyme system. Glucose oxidase (EC 1.1.3.4) and peroxidase (EC 1.11.1.7) were immobilized together into an artificial proteic membrane obtained by a previously described co-cross-linking process using a bifunctional agent, glutaraldehyde. The cytochemical reagent 3,3'-diaminobenzidine was used as a hydrogen donor substrate and kinetic studies were performed with both free and immobilized forms of the enzymes; in the latter case, a new direct method was introduced which allowed kinetic studies on the visualization system itself. From experimental kinetic parameters, theoretical concentrations profiles were calculated by computer using numerical analysis methods. These results were discussed with special attention to the electron microscopic observations. Computer simulations were in good agreement with electron micrographs. No geometrical similarity was seen in our system between poly(3,3'-diaminobenzidine) precipitate distribution and peroxidase molecule homogeneous location.

The presynaptic action of L-glutamate at the crayfish neuromuscular junction. Results obtained by intra-axonal recordings and nerve terminal damage.

The presynaptic action of glutamate was investigated in crayfish neuromuscular preparations. The excitability of locally stimulated nerve terminals increased during the perfusion of glutamate. Electrotonically propagated depolarizations were recorded in the excitatory axons when glutamate was ionophoretically applied to sensitive spots on the muscle membrane. Depolarizations of the axon were also obtained when glutamate, GABA and aspartate were added to the bath. In order to evaluate the part of the presynaptic effect in the depolarization induced in muscle fibres, nerve terminals were damaged either by treatment with high-Ca solutions or by denervation. In both cases, a decreased sensitivity to glutamate was found. Possible relationships between the nerve terminal damage and the change in the response to glutamate are proposed.

[Mitochondrial localization of enzymes linked to glycogen metabolism in the snail sperm cell]. / Localisation mitochondriale d'enzymes liees au metabolisme du glycogene dans le spermatozoide de l'escargot.

The mitochondrial derivative of the sperm cell of the Gastropod Helix is endowed with a compartment loaded with glycogen (Personne et André, 1964). The aim of this work is to establish whether this mitochondrial glycogen is synthesized in the mitochondrial derivative itself or elsewhere in the cell. For this purpose, living sperm were first incubated in a medium containing glucose 1-phosphate, then fixed, sectioned, and stained specifically for polysaccharides by the phosphotungstic acid technique or the periodic acid-thiosemicarbazide-silver proteinate technique. Comparison with controls shows that a synthesis of glycogen occurred during the time of incubation. It can be inferred from this result that an amylophosphorylase system controlling the metabolism of polysaccharides is present in the mitochondrial derivative itself. Results obtained with the iodine technique indicate that the original glycogen molecules are elongated during the experiment. It seems probable that the amylophosphorylase system demonstrated here accounts for at least a part of the proteinaceous coat morphologically detectable around each individual glycogen particle.

The localization of glycogen in the spermatozoa of various invertebrate and vertebrate species.

With the periodic acid-thiosemicarbazide-silver proteinate procedure for the detection of polysaccharides in thin sections, glycogen is localized in the cavities of centrioles and basal bodies, within the axoneme (and surrounding it), in mitochondria, and in the "packing" cytoplasm of the middle piece of spermatozoa of several invertebrate and vertebrate species. The cytochemical localization of glycogen is verified by extraction with alpha-amylase solution. These findings establish the existence of stored glycogen in sperm. The polysaccharide presumably serves as an endogenous source of energy in the absence of extracellular metabolites, under either aerobic or anaerobic conditions. Other hypotheses on the physiological significance of intracellular glycogen stores in sperm are discussed. Sperm that store glycogen contain some enzymes of glycogen metabolism. In the presence of glucose-1-phosphate, ATP, and Mg(++) ions, an amylophosphorylase catalyzes the in vivo synthesis of glycogen. The newly formed product resembles gamma-particles, and is digestible with alpha-amylase.