B cell analysis of ethnic groups in Mali with differential susceptibility to malaria

ABSTRACT: BACKGROUND: Several studies indicate that people of the Fulani ethnic group are less susceptible to malaria compared to those of other ethnic groups living sympatrically in Africa, including the Dogon ethnic group. Although the mechanisms of this protection remain unclear, the Fulani are known to have higher levels of Plasmodium falciparum-specific antibodies of all Ig classes as compared to the Dogon. However, the proportions of B cell subsets in the Fulani and Dogon that may account for differences in the levels of Ig have not been characterized. METHODS: In this cross-sectional study, venous blood was collected from asymptomatic Fulani (n=25) and Dogon (n=25) adults in Mali during the malaria season, and from P. falciparum-naive adults in the U.S. (n=8). At the time of the blood collection, P. falciparum infection was detected by blood-smear in 16% of the Fulani and 40% of the Dogon volunteers. Thawed lymphocytes were analysed by flow cytometry to quantify B cell subsets, including immature and naive B cells; plasma cells; and classical, activated, and atypical memory B cells (MBCs). RESULTS: The overall distribution of B cell subsets was similar between Fulani and Dogon adults, although the percentage of activated MBCs was higher in the Fulani group (Fulani: 11.07% [95% CI: 9.317 - 12.82]; Dogon: 8.31% [95% CI: 6.378 - 10.23]; P=0.016). The percentage of atypical MBCs was similar between Fulani and Dogon adults (Fulani: 28.3% [95% CI: 22.73 - 34.88]; Dogon: 29.3% [95% CI: 25.06 - 33.55], but higher than U.S. adults (U.S.: 3.0% [95% CI: -0.21 - 6.164]; P<0.001). Plasmodium falciparum infection was associated with a higher percentage of plasma cells among Fulani (Fulani infected: 3.3% [95% CI: 1.788 - 4.744]; Fulani uninfected: 1.71% [95% CI: 1.33 - 2.08]; P=0.011), but not Dogon adults. CONCLUSION: These data show that the malaria-resistant Fulani have a higher percentage of activated MBCs compared to the Dogon, and that P. falciparum infection is associated with a higher percentage of plasma cells in the Fulani compared to the Dogon, findings that may account for the higher levels of P. falciparum antibodies in the Fulani.     

A novel function of Ubc13 in TNFR1 receptor activation

The tumour necrosis factor receptor 1 (TNFR1) activates prosurvival pathways by induction of the NFkappaB pathway and induces cell death via apoptosis. The ubiquitin-conjugating enzyme, Ubc13, mediates the ubiquitylation-dependent formation of protein complexes crucial for the activation and regulation of both pathways. We describe a new role for Ubc13 in the regulation of TNFR1 activity after UV stimulation. Depletion of Ubc13 by RNAi produced a decreased NFkappaB activity and increased apoptosis after stimulation by TNFalpha and UV-C light. These results are consistent with the function of Ubc13 in the ubiquitylation of RIP1, which controls the proapoptotic or prosurvival response after TNFR1 activation. Moreover, we demonstrated that UV-C light induces a close interaction between the Ubc13 protein and the TNFR1 receptor. In the absence of Ubc13 TNFR1 clustering was increased. We conclude that Ubc13 has a regulatory role for the activation of TNFR1 and hence, apoptotic cell death. Thus, our results elucidated a new role for Ubc13 in the regulation of prosurvival or proapoptotic processes, which is upstream of so far investigated functions.     

Rac is a dominant regulator of cadherin-directed actin assembly that is activated by adhesive ligation independently of Tiam1

Classic cadherins function as adhesion-activated cell signaling receptors. On adhesive ligation, cadherins induce signaling cascades leading to actin cytoskeletal reorganization that is imperative for cadherin function. In particular, cadherin ligation activates actin assembly by the actin-related protein (Arp)2/3 complex, a process that critically affects the ability of cells to form and extend cadherin-based contacts. However, the signaling pathway(s) that activate Arp2/3 downstream of cadherin adhesion remain poorly understood. In this report we focused on the Rho family GTPases Rac and Cdc42, which can signal to Arp2/3. We found that homophilic engagement of E-cadherin simultaneously activates both Rac1 and Cdc42. However, by comparing the impact of dominant-negative Rac1 and Cdc42 mutants, we show that Rac1 is the dominant regulator of cadherin-directed actin assembly and homophilic contact formation. To pursue upstream elements of the Rac1 signaling pathway, we focused on the potential contribution of Tiam1 to cadherin-activated Rac signaling. We found that Tiam1 or the closely-related Tiam2/STEF1 was recruited to cell-cell contacts in an E-cadherin-dependent fashion. Moreover, a dominant-negative Tiam1 mutant perturbed cell spreading on cadherin-coated substrata. However, disruption of Tiam1 activity with dominant-negative mutants or RNA interference did not affect the ability of E-cadherin ligation to activate Rac1. We conclude that Rac1 critically influences cadherin-directed actin assembly as part of a signaling pathway independent of Tiam1. actin cytoskeleton; Cdc42; E-cadherin     

Differential effects of cyclophosphamide and mycophenolate mofetil on cellular and serological parameters in patients with systemic lupus erythematosus

IntroductionDisease activity and therapy show an impact on cellular and serological parameters in patients with systemic lupus erythematosus (SLE). This study was performed to compare the influence of mycophenolate mofetil (MMF) and cyclophosphamide (CYC) therapy on these parameters in patients with flaring, organ-threatening disease.MethodsSLE patients currently receiving CYC (n = 20), MMF (n = 25) or no immunosuppressive drugs (n = 22) were compared using a cross-sectional design. Median disease activity and daily corticosteroid dose were similar in these treatment groups. Concurrent medication, organ manifestations, and disease activity were recorded, and cellular and serological parameters were determined by routine diagnostic tests or flow cytometric analysis. In addition follow-up data were obtained from different sets of patients (CYC n = 24; MMF n = 23).ResultsAlthough both drugs showed a significant effect on disease activity and circulating B cell subsets, only MMF reduced circulating plasmablasts and plasma cells as well as circulating free light chains within three months of induction therapy. Neither MMF nor CYC were able to reduce circulating memory B cells. MMF lowered IgA levels more markedly than CYC. We did not observe a significant difference in the reduction of IgG levels or anti-dsDNA antibodies comparing patients receiving MMF or CYC. In contrast to MMF, induction therapy with CYC was associated with a significant increase of circulating CD8+ effector T cells and plasmacytoid dendritic cells (PDCs) after three months.ConclusionsThe results indicate differences between MMF and CYC with regard to the mechanism of action. MMF, but not CYC, treatment leads to a fast and enduring reduction of surrogate markers of B cell activation, such as circulating plasmablasts, plasma cells and free light chains but a comparable rate of hypogammaglobulinemia.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0603-8) contains supplementary material, which is available to authorized users.     

Type 2 diabetes in non-obese Indian subjects is associated with reduced leptin levels: Study from Mumbai, Western India

Objective: Asian Indian subjects have a high tendency to develop Type 2 diabetes even though obesity is relatively uncommon. We evaluated the serum leptin levels in a group of non-obese Type 2 diabetic patients from Mumbai, Western India.Design: Cross sectional study.Methods: A total of 104 subjects consisting of 28 with Type 2 diabetes, 16 with impaired glucose tolerance and 60 age and sex-matched control subjects were given 75 g oral glucose tolerance test. Fasting serum leptin (IRMA), insulin and C-peptide were measured along with fasting and 2 h plasma glucose. The relation between these variables was studied by univariate and multiple regression analysis.Results: Type 2 diabetes was associated with marked (50–60%) reduction in serum leptin levels, in both men and women. Women, but not men, with impaired glucose tolerance exhibited 60% lower leptin. Serum leptin levels were positively correlated to body mass index (BMI; r = 0.501, p = 0.001) and calculated body fat percent (r = 0.525, p = 0.001) in all the study subjects with a better correlation in the normal subjects (r = 0.562 for BMI and 0.735 for body fat). On the other hand, serum leptin showed significant correlation to serum insulin (r = 0.362, p = 0.008) only in subjects with diabetes or IGT. In the multiple regression model, BMI was the only independent predictor of leptin, in all the subjects. However, in subjects with diabetes or impaired glucose tolerance, waist circumference (p = 0.003), gender (p = 0.007) and body fat (p = 0.009) were significant predictors of leptin, besides BMI. Gender-specific multiple regression revealed serum insulin as an independent predictor of leptin in men (p = 0.026). Therefore, lower serum leptin levels in diabetes is partly due to increased waist circumference, decreased BMI and male sex. These observations are consistent with the view that leptin levels in this cohort of non-obese Indians from Mumbai exhibit gender-specific relationship partly attributed to changes in serum insulin and waist circumference in men and to changes in BMI, in women.     

Memory T cells protect against Plasmodium vivax infection

Immunity induced by Plasmodium vivax infection leads to memory T cell recruitment activated during "relapse" or "re-infection". This study aims to characterise memory T cells in patients with acute or convalescent P. vivax infection. Lymphocytes were collected from patients infected by P. vivax, immune controls and naive controls. The proportion of immature memory T cells, expressing CD45RO(+)CD27(+), and mature cells lacking CD27 was assessed. A statistically significant increase in the median percentage of memory T cell subsets expressing CD4(+) was observed in material from patients with an acute infection compared with that from either naive or immune controls. The high percentage of memory T cells in infected patients was maintained until 60 days post treatment. The immune controls living in a malaria endemic area had a somewhat increased proportion of memory T cell subsets expressing CD8(+). An approximately three-fold increase of these cell types was shown in patients with an acute infection and the level persisted until 60 days post treatment. Phenotypic characterisation of the peripheral lymphocytes during acute infection revealed that a large fraction of the lymphocytes carried the gammadelta phenotypes suggesting a role for these cells in the early response against P. vivax. Very low levels of P. vivax specific antibody were found. This might suggest that cell-mediated immunity may play a greater role in the development of naturally acquired protection against P. vivax infection than humoral immunity. Our results provide further insight into the mechanism of cell-mediated immunity to P. vivax infection that could be important for the future development of a successful vaccine and anti-malarial drug designation.     

Functions of the segment polarity genes midline and H15 in Drosophila melanogaster neurogenesis

The Drosophila melanogaster ventral nerve cord derives from neural progenitor cells called neuroblasts. Individual neuroblasts have unique gene expression profiles and give rise to distinct clones of neurons and glia. The specification of neuroblast identity provides a cell intrinsic mechanism which ultimately results in the generation of progeny which are different from each other. Segment polarity genes have a dual function in early neurogenesis: within distinct regions of the neuroectoderm, they are required both for neuroblast formation and for the specification of neuroblast identity. Previous studies of segment polarity gene function largely focused on neuroblasts that arise within the posterior part of the segment. Here we show that the segment polarity gene midline is required for neuroblast formation in the anterior-most part of the segment. Moreover, midline contributes to the specification of anterior neuroblast identity by negatively regulating the expression of Wingless and positively regulating the expression of Mirror. In the posterior-most part of the segment, midline and its paralog, H15, have partially redundant functions in the regulation of the NB marker Eagle. Hence, the segment polarity genes midline and H15 play an important role in the development of the ventral nerve cord in the anterior- and posterior-most part of the segment.     

Behavioral profiles and stress-induced corticosteroid secretion in male Wistar rats subjected to short and prolonged periods of maternal separation

Early life experiences are important for the development of neurobiobehavioral mechanisms and subsequent establishment of mental functions. In experimental animals, early life experiences can be studied using the maternal separation model. Maternal separation has been described to induce neurobiological changes and thus affect brain function, mental state and behavior. We have established a protocol in order to study the effects of repeated short and prolonged periods of maternal separation during the postnatal period on adult neurochemistry, voluntary ethanol intake and behavior. In the present experiment, we focus on the long-term effects of maternal separation on exploration and risk assessment behavior as well corticosteroid secretion. Rat pups were assigned to 15 min (MS15) or 360 min (MS360) of daily maternal separation and normal animal facility rearing (AFR) during postnatal days 1-21. To establish the adult behavioral profile in male rats, three tests were used: the Concentric Square Field (CSF), the Open Field (OF) and the Elevated Plus-maze (EPM). No differences between the three experimental groups were found in the traditional OF and EPM tests. The CSF test indicated that the MS360 rats were more explorative and expressed an altered risk assessment and risk-taking profile. In response to a restraint stress, MS360 rats had a blunted corticosterone release in contrast to MS15 and AFR rats. In contrast to previous results, the outcome of the present investigation does not support the notion that a prolonged period of maternal separation results in an adult phenotype characterized by an increased emotional reactivity.     

Flow mechanotransduction regulates traction forces, intercellular forces, and adherens junctions

Endothelial cells respond to fluid shear stress through mechanotransduction responses that affect their cytoskeleton and cell-cell contacts. Here, endothelial cells were grown as monolayers on arrays of microposts and exposed to laminar or disturbed flow to examine the relationship among traction forces, intercellular forces, and cell-cell junctions. Cells under laminar flow had traction forces that were higher than those under static conditions, whereas cells under disturbed flow had lower traction forces. The response in adhesion junction assembly matched closely with changes in traction forces since adherens junctions were larger in size for laminar flow and smaller for disturbed flow. Treating the cells with calyculin-A to increase myosin phosphorylation and traction forces caused an increase in adherens junction size, whereas Y-27362 cause a decrease in their size. Since tugging forces across cell-cell junctions can promote junctional assembly, we developed a novel approach to measure intercellular forces and found that these forces were higher for laminar flow than for static or disturbed flow. The size of adherens junctions and tight junctions matched closely with intercellular forces for these flow conditions. These results indicate that laminar flow can increase cytoskeletal tension while disturbed flow decreases cytoskeletal tension. Consequently, we found that changes in cytoskeletal tension in response to shear flow conditions can affect intercellular tension, which in turn regulates the assembly of cell-cell junctions.     

Lack of significant influence for FcγRIIa-RH131 or hemoglobin AA/AS polymorphisms on immunity and susceptibility to uncomplicated malaria and existence of marked linkage between the two polymorphisms in Daraweesh

Malaria signature on human genome is marked by several gene polymorphisms. HemoglobinAS (HbAS) is known to protect against severe malaria, but barely proved to protect against uncomplicated malaria (UM). Similarly, the influence of FcγRIIa-RH131 polymorphism on malaria is controversial. Polymorphisms in both genes were examined and levels of IgG subclasses against four malaria antigens were measured for 250 Fulani’s from Daraweesh, eastern Sudan. Morbidity data for up to nine years was available for 214 donors. Number of malaria episodes experienced by each individual during the study period was used as indicator for susceptibility to UM. PCR and RFLP were used for donors DNA genotyping and ELISA for antibodies measurement. Results revealed that neither FcγRIIa-RH131 alleles/genotypes nor HbAA/AS was significantly associated with malaria morbidity or with levels of IgG to test antigens. Both polymorphisms were in Hardy–Weinberg Equilibrium, interestingly, there was strong association between the two polymorphisms (linkage disequilibrium – LD) with D′ = 0.89. The association between the two polymorphisms was confirmed by analysis of independent material from a neighboring village. In conclusion, in Daraweesh both FcγRIIa-RH131 and HbAA/AS genotypes, independently or together, were not major markers for UM susceptibility, however, marked LD was observed between the two polymorphisms.