On the dynamics of predation risk perception for a vigilant forager

There has been much recent interest in modelling epidemics on networks, particularly in the presence of substantial clustering. Here, we develop pairwise methods to answer questions that are often addressed using epidemic models, in particular: on the basis of potential observations early in an outbreak, what can be predicted about the epidemic outcomes and the levels of intervention necessary to control the epidemic? We find that while some results are independent of the level of clustering (early growth predicts the level of ‘leaky’ vaccine needed for control and peak time, while the basic reproductive ratio predicts the random vaccination threshold) the relationship between other quantities is very sensitive to clustering.     

Inactivation and reactivation of a variant-specific antigen gene in cyclically transmitted Trypanosoma brucei.

In Trypanosoma brucei, the activation of the variant-specific antigen gene AnTat 1.1 proceeds by the synthesis of an additional gene copy, the AnTat 1.1 ELC, which is transposed to a new location, the expression site, where it is transcribed. Using the AnTat 1.1 variant to infect flies, we investigated the fate of the AnTat 1.1 ELC during cyclic transmission of T. brucei. We show here that the AnTat 1.1 ELC is conserved in procyclic trypanosomes, obtained either from the midgut of infected Glossina or from cultures, and in metacyclic trypanosomes, although the AnTat 1.1 serotype is not detected among metacyclic antigen types. This same AnTat 1.1 ELC, which is thus silent as the parasite develops in the insect vector, can be reactivated without duplication during the first parasitemia wave following cyclical transmission. This re-expression of the conserved ELC accounts for the early appearance of the 'ingested' antigenic type after passage through the fly.     

Changes in "template-bound" and "free" RNA polymerase activities in isolated nuclei from Xenopus laevis embryos

Nuclei have been isolated from Xenopus laevis embryos and incubated under conditions allowing RNA synthesis to proceed for more than 3 h. The RNA molecules synthesized on the endogenous template are stable, heterogeneous in size and correspond to the activities of the three RNA polymerases.In these in vitro conditions we have determined the extent of activity of the three RNA polymerases during the embryonic development from blastula to swimming tadpole. Our results on isolated nuclei are in good agreement with the changes in RNA synthesis which take place during normal embryonic development.We have measured both the “template-bound” and the “free” activities of each of the three RNA polymerases during development. Amongst the total RNA polymerase activities engaged on the template, the proportion of polymerase I increases as development proceeds: at the blastula stage, there is practically no RNA polymerase I engaged on the template, whereas in swimming tadpoles, RNA polymerase I amounts to about 90% of the RNA polymerases bound to the DNA. Conversely, RNA polymerase I represents the major part of free RNA polymerases in blastula nuclei.Autoradiography of incubated nuclei shows that, at least in swimming tadpoles nuclei, both “free” and “template-bound” RNA polymerase I are localized in the nucleoli.The evolution of “template-bound” RNA polymerase II activity during development is quite different from that of RNA polymerase I: RNA polymerase II activity represents 75% of engaged polymerase activity in blastulae and only 47% at the swimming tadpoles stage.The results suggest that part of the “free” RNA polymerase I activity might progressively become “template-bound” during embryogenesis.     

Molecular Consequences of Proprotein Convertase 1/3 (PC1/3) Inhibition in Macrophages for Application to Cancer Immunotherapy: A Proteomic Study

Macrophages provide the first line of host immune defense. Their activation triggers the secretion of pro-inflammatory cytokines and chemokines recruiting other immune cells. In cancer, macrophages present an M2 anti-inflammatory phenotype promoting tumor growth. In this way, strategies need to be develop to reactivate macrophages. Previously thought to be expressed only in cells with a neural/neuroendocrine phenotype, the proprotein convertase 1/3 has been shown to also be expressed in macrophages and regulated as a function of the Toll-like receptor immune response. Here, we investigated the intracellular impact of the down-regulation of the proprotein convertase 1/3 in NR8383 macrophages and confirmed the results on macrophages from PC1/3 deficient mice. A complete proteomic study of secretomes and intracellular proteins was undertaken and revealed that inhibition of proprotein convertase 1/3 orient macrophages toward an M1 activated phenotype. This phenotype is characterized by filopodial extensions, Toll-like receptor 4 MyD88-dependent signaling, calcium entry augmentation and the secretion of pro-inflammatory factors. In response to endotoxin/lipopolysaccharide, these intracellular modifications increased, and the secreted factors attracted naïve T helper lymphocytes to promote the cytotoxic response. Importantly, the application of these factors onto breast and ovarian cancer cells resulted in a decrease viability or resistance. Under inhibitory conditions using interleukin 10, PC1/3-knockdown macrophages continued to secrete inflammatory factors. These data indicate that targeted inhibition of proprotein convertase 1/3 could represent a novel type of immune therapy to reactivate intra-tumoral macrophages.Innate immunity is the first line of immune defense and is common to all metazoans (1, 2). In this immune system, macrophages play a crucial role in the maintenance of tissue homeostasis. These cells are involved in almost every disease through their immunological and wound-healing functions (1, 2). During a pathogenic infection, trauma or neurodegeneration, macrophages are recruited and activated contributing to the phagocytosis of pathogens and the secretion of cytokines and chemokines activating other immune cells. Macrophages can develop into classically pro-inflammatory (M1) or alternatively (M2) activated macrophages. M1 macrophages are characterized by the secretion of pro-inflammatory cytokines whereas M2 macrophages secrete anti-inflammatory cytokines (3). Stimulation of macrophages with LPS activates TLR4 signaling leading to the nucleus translocation of NF-κB or IRF3 which activate genes encoding proteins involved in innate immune response (4). Many of these proteins are secreted (cytokines, chemokines…) to attract and activate other immune cells like T lymphocytes. In tumors, macrophages are oriented toward the M2 phenotype and promote cancer growth by suppressing immune cells function (5). Current research in the therapeutic field focus on ways to reactivate macrophages.Surprisingly, we have shown that during immune responses, macrophages secrete typical neuroendocrine molecules (6–8), such as neuropeptides (9) or the proprotein convertases (PC)¹ PC2 and PC1/3 and that PC1/3 is an important regulator of innate immune responses (10–12). Proprotein convertases cleave precursor proteins which can lead to the activation, inactivation or functional changes. PC2 and PC1/3 operate within the regulated secretory pathway. Their expression is not restricted to neuroendocrine tissues, they are also expressed in macrophages and lymphocytes (12). In a previous study from our group, PC1/3 knockout (KO) in mice challenged with LPS caused innate immune defects and uncontrolled cytokine secretion (10). Th1 pathway is enhanced in PC1/3 KO mice. Following LPS treatment, PC1/3 colocalized with TLR4 in the endosomal compartment (11). We concluded that PC1/3 contributes to the regulation of TLR4 signaling and the resulting cytokine secretion.The NR8383 rat pulmonary macrophage cell line was previously shown as a good model to study the role of PC1/3 in the macrophage innate immune response (13). In the present study, we developed a PC1/3-knockdown (K_D) NR8383 cell line using lentiviral-delivered shRNAs. Our aim is to understand the cellular impact of PC1/3 inhibition in macrophages and the consequences on their activation. Proteomic analysis of secreted proteins allowed us to identify pro-inflammatory cytokines and alarmins already at 24h of LPS stimulation in PC1/3-K_D secretomes which was confirmed by cytokines array. Proteomic studies of PC1/3-K_D NR8383 cellular extracts revealed an important perturbation in the intracellular trafficking machinery through the disorganization of cytoskeletal protein expression. These results were confirmed on macrophages from PC1/3 KO mice. Cytokines secretion and cytoskeleton reorganization can be linked to intracellular calcium increase in PC1/3-K_D cells. Moreover, we showed that MyD88-dependant TLR4 signaling was sustained when PC1/3 is down-regulated. We describe here that inhibition of PC1/3 induced classically activated phenotype (M1) in macrophages. The chemotactic and anti-tumor properties of the PC1/3-K_D macrophage secretome promoted the cytotoxic immune response and inhibited cancer cell viability. The down-regulation of PC1/3 could be used in cancer immunotherapy to reactivate macrophages.     

Detecting predators and locating competitors while foraging: an experimental study of a medium-sized herbivore in an African savanna

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.