Variation in exposure to Anopheles gambiae salivary gland peptide (gSG6-P1) across different malaria transmission settings in the western Kenya highlands

ABSTRACT: BACKGROUND: The existing metrics of malaria transmission are limited in sensitivity under low transmission intensity. Robust surveillance systems are needed as interventions to monitor reduced transmission and prevention of rapid reintroduction. Serological tools based on antibody responses to parasite and vector antigens are potential tools for transmission measurements. The current study sought to evaluate antibody responses to Anopheles gambiae salivary gland peptide (gSG6- P1), as a biomarker of human exposure to Anopheles bites, in different transmission settings and seasons. The comparison between anti-MSP-119 IgG immune responders and non-responders allowed exploring the robustness of the gSG6-P1 peptide as a surveillance tool in an area of decreasing malaria transmission. METHODS: Total IgG levels to gSG6-P1 were measured in an age-stratified cohort (< 5, 5-14 and [greater than or equal to] 15 years) in a total of 1,366 participants from three localities in western Kenya [Kisii (hypoendemic), Kakamega (mesoendemic), and Kombewa (hyperendemic)] including 607 sera that were additionally tested for MSP-119 specific responses during a low and a high malaria transmission seasons. Antibody prevalence and levels were compared between localities with different transmission intensities. Regression analysis was performed to examine the association between gSG6-P1 and MSP-119 seroprevalence and parasite prevalence. Result Seroprevalence of gSG6-P1 in the uphill population was 36 % while it was 50 % valley bottom (chi2 = 13.2, df = 1, p < 0.001). Median gSG6-P1 antibody levels in the Valley bottom were twice as high as that observed in the uphill population [4.50 vs. 2.05, p < 0.001] and showed seasonal variation. The odds of gSG6-P1 seropositives having MSP-119 antibodies were almost three times higher than the odds of seronegatives (OR = 2.87, 95 % CI [1.977, 4.176]). The observed parasite prevalence for Kisii, Kakamega and Kombewa were 4 %, 19.7 % and 44.6 % whilst the equivalent gSG6-P1 seroprevalence were 28 %, 34 % and 54 %, respectively. CONCLUSION: The seroprevalence of IgG to gSG6-P1 was sensitive and robust in distinguishing between hypo, meso and hyper transmission settings and seasonal fluctuations.     

Compound heterozygosity at the sphingomyelin phosphodiesterase-1 (SMPD1) gene is associated with low HDL cholesterol

Type A and B forms of Niemann-Pick disease (NPD) are lipid storage disorders caused by deficient activity of the enzyme acid sphingomyelinase (aSMase) and the resulting accumulation of sphingomyelin in tissues. In the present study, we investigated two family members who had been diagnosed with Type B NPD and who had a severe decrease in plasma high density lipoprotein cholesterol (HDL-C). The proband (a 48-year-old male) had an HDL-C of 0.30 mmol/l (12 mg/dl) and his sister had values of 0.45 mmol/l (17 mg/dl) with severe premature coronary artery disease (CAD). Hypertriglyceridemia was found in both cases. aSMase activity measured in skin fibroblasts appeared markedly depressed. The SMPD1 gene, coding for aSMase, was sequenced in affected subjects and all family members. Compound heterozygosity (DeltaR608 and R441X) was identified in both affected patients. Carriers of the DeltaR608 mutation tended to have moderately to severe decreased HDL-C levels, whereas carriers of the R441X mutation, although present only in young subjects (<20 years of age) had normal HDL-C levels. To investigate the cause of the low HDL-C level in these patients, we studied apoA-I-mediated cellular cholesterol efflux in fibroblasts. Unlike patients with Tangier disease, cholesterol efflux was found to be normal under the experimental conditions used in the present study. On the other hand, we observed a significant increase in the free cholesterol:esterified cholesterol ratio in HDL fraction from these patients and a decrease in endogenous lecithin-cholesterol acyltransferase (LCAT) activity, as determined by the fractional esterification rate. Taken together, these results suggest that (1) compound heterozygosity at the SMPD1 gene causes a severe decrease in aSMase activity and in HDL-C and increases the risk of CAD, (2) this lipoprotein abnormality is not attributable to defective cellular cholesterol efflux, (3) abnormal HDL composition might cause a decrease in LCAT activity and a lack of HDL maturation.     

Structural modification of plasma HDL by phospholipids promotes efficient ABCA1-mediated cholesterol release

It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates prebeta(1)-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated prebeta(1)-LpA-I-like particles inhibited the binding of (125)I-apoA-I to ABCA1 more efficiently than HDL(3) (IC(50) = 2.20 +/- 0.35 vs. 37.60 +/- 4.78 microg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased ( approximately 50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native prebeta(1)-LpA-I and prebeta(1)-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither prebeta(1)-LpA-I nor free cholesterol efflux. These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from alpha-HDL to prebeta-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma prebeta(1)-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease.     

Complexation of uranium (VI) by three eco-types of Acidithiobacillus ferrooxidans studied using time-resolved laser-induced fluorescence spectroscopy and infrared spectroscopy

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used to study the properties of uranium complexes (emission spectra and fluorescence lifetimes) formed by the cells of the three recently described eco-types of Acidithiobacillus ferrooxidans. The results demonstrated that these complexes have different lifetimes which increase in the same order as the capability of the strains to accumulate uranium. The complexes built by the cells of the eco-type II were the strongest, whereas, those of the eco-types I and III were significantly weaker. The emission spectra of all A. ferrooxidans complexes were almost identical to those of the uranyl organic phosphate compounds. The latter finding was confirmed by infrared spectroscopic analysis.     

Thirty years of stimulus-secretion coupling: from Ca(2+) toGTP in the regulation of exocytosis

Calcium, initially considered as the universal link between receptor stimulation and the onset of exocytosis in secretory cells, is now recognised as only one of a number of intracellular activators. In cells of haematopoietic origin (including mast cells), the key activator is one or more GTPases. Cells of this class, stimulated with GTPgammaS can undergo exocytosis in the effective absence of Ca(2+). A number of GTP-binding proteins that mediate exocytosis (G(E)) have been proposed but the best evidence supports roles for members of the Rho family of monomeric GTPases and for betagamma-subunits derived from G(i3). While preactivated Rac and Cdc42 can induce secretion from permeabilised mast cells in the absence of a guanine nucleotide betagamma-subunits only act to enhance the secretion induced by other GTP-binding proteins (likely to be members of the Rho family of monomeric GTPases). Further work is required to identify downstream effectors activated by these GTP-binding proteins and to show how they interact with the SNAP and SNARE isoforms known to be present in these cells.     

Practical considerations regarding the use of streptolysin-O as a permeabilising agent for cells in the investigation of exocytosis

Streptolysin-O is widely used in cell biological investigations in order to make large (>12 nm) pores in the plasma membrane and so to render the cytosol directly accessible to experimental manipulation. We have compared the effect of streptolysin-O commercially formulated (Murex Diagnostics) as a diagnostic reagent in pathology with two pure reagents (a conventional purified protein, and a recombinant protein generated in E.coli) on exocytotic secretion from mast cells. For mast cells permeabilised by streptolysin obtained from the commercial source, exocytosis (of -D-N-acetylglucosaminidase) is dependent on provision of both Ca²⁺ and a guanine nucleotide. In contrast, for cells permeabilised by either of the two pure proteins, a substantial extent of Ca²⁺-independent exocytosis can be elicited. When the Murex material is subject to dialysis or ultrafiltration, some secretion can be induced in the absence of Ca²⁺, indicating a modulatory function of the low mol wt additives of formulation, mainly phosphate and cysteine. However, Ca²⁺-independent exocytosis is still manifest when the pure proteins are reconstituted with ultrafiltrates from the Murex material. These observations indicate that reagents used to permeabilise cells should be characterised thoroughly and used with great care. Confirmation that the cytolytic activity of the Murex material derives from a cholesterol directed factor was demonstrated by inhibition of exocytosis when red blood cell derived (and hence cholesterol containing) sonicated liposomes were provided.     

Signal transduction and functional changes in neutrophils with aging

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first-line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor-driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.     

Taxonomic Composition and Trophic Structure of the Continental Bony Fish Assemblage from the Early Late Cretaceous of Southeastern Morocco

The mid-Cretaceous vertebrate assemblage from south-eastern Morocco is one of the most diversified continental vertebrate assemblages of this time worldwide. The bony fish component (coelacanths, lungfishes and ray-finned fishes) is represented by relatively complete specimens and, mostly, by fragmentary elements scattered along 250 kilometres of outcrops. Here we revisit the bony fish assemblage by studying both isolated remains collected during several fieldtrips and more complete material kept in public collections. The assemblage comprises several lungfish taxa, with the first mention of the occurrence of Arganodus tiguidiensis, and possibly two mawsoniid coelacanths. A large bichir cf. Bawitius, is recorded and corresponds to cranial elements initially referred to ‘Stromerichthys’ from coeval deposits in Egypt. The ginglymodians were diversified with a large ‘Lepidotes’ plus two obaichthyids and a gar. We confirm here that this gar belongs to a genus distinctive from Recent gars, contrary to what was suggested recently. Teleosteans comprise a poorly known ichthyodectiform, a notopterid, a probable osteoglossomorph and a large tselfatiiform, whose cranial anatomy is detailed. The body size and trophic level for each taxon are estimated on the basis of comparison with extant closely related taxa. We plotted the average body size versus average trophic level for the Kem Kem assemblage, together with extant marine and freshwater assemblages. The Kem Kem assemblage is characterized by taxa of proportionally large body size, and by a higher average trophic level than the trophic level of the extant compared freshwater ecosystems, but lower than for the extant marine ecosystems. These results should be regarded with caution because they rest on a reconstructed assemblage known mostly by fragmentary remains. They reinforce, however, the ecological oddities already noticed for this mid-Cretaceous vertebrate ecosystem in North Africa.     

The HOXB4 homeoprotein promotes the ex vivo enrichment of functional human embryonic stem cell-derived NK cells

Human embryonic stem cells (hESCs) can be induced to differentiate into blood cells using either co-culture with stromal cells or following human embryoid bodies (hEBs) formation. It is now well established that the HOXB4 homeoprotein promotes the expansion of human adult hematopoietic stem cells (HSCs) but also myeloid and lymphoid progenitors. However, the role of HOXB4 in the development of hematopoietic cells from hESCs and particularly in the generation of hESC-derived NK-progenitor cells remains elusive. Based on the ability of HOXB4 to passively enter hematopoietic cells in a system that comprises a co-culture with the MS-5/SP-HOXB4 stromal cells, we provide evidence that HOXB4 delivery promotes the enrichment of hEB-derived precursors that could differentiate into fully mature and functional NK. These hEB-derived NK cells enriched by HOXB4 were characterized according to their CMH class I receptor expression, their cytotoxic arsenal, their expression of IFNγ and CD107a after stimulation and their lytic activity. Furthermore our study provides new insights into the gene expression profile of hEB-derived cells exposed to HOXB4 and shows the emergence of CD34(+)CD45RA(+) precursors from hEBs indicating the lymphoid specification of hESC-derived hematopoietic precursors. Altogether, our results outline the effects of HOXB4 in combination with stromal cells in the development of NK cells from hESCs and suggest the potential use of HOXB4 protein for NK-cell enrichment from pluripotent stem cells.     

Modulation of T-cell signalling by non-esterified fatty acids

Polyunsaturated fatty acids (PUFAs) have been shown to be immunosuppressive. In particular, they can decrease important T-cell functions that may have a profound impact on the acquired immune response. Several mechanisms may explain the immunosuppressive properties of PUFAs. Here we review the mechanisms by which they interfere with T-cell activation. PUFAs affect lipid rafts composition and function that play an essential role in T-cell signalling. The possible physiological and pathological significances of this immunomodulation by PUFAs are discussed. Further mechanistic studies and randomized controlled clinical trials are needed to assess more accurately their effects in healthy and pathological states.