An arginase 2 promoter transgenic illuminates immune cell polarisation in zebrafish

The innate immune response to inflammation and infections are complex and represent major challenges for developing much needed new treatments for chronic inflammatory diseases and drug resistant infections. To be ultimately successful, the immune response must be balanced to allow pathogen clearance without excess tissue damage, processes controlled by pro- and anti-inflammatory signals. The roles of anti-inflammatory signalling in raising an appropriate immune response are underappreciated, representing overlooked potential drugs targets. This is especially true in neutrophils, a difficult cell type to study ex vivo due to a short lifespan, dogmatically seen as being highly pro-inflammatory. Here, we have generated and describe the first zebrafish transgenic line that labels expression of an anti-inflammatory gene (TgBAC(arg2:eGFP)sh571) and show that a subpopulation of neutrophils upregulate arginase early after immune challenge with injury and infection. At wound healing stages, arg2:GFP is expressed in subsets of neutrophils and macrophages, potentially representing anti-inflammatory, polarised immune cell populations. Our findings identify nuanced responses to immune challenge in vivo, responses that represent new opportunities for therapeutic interventions during inflammation and infection.

Occurrence of foamy macrophages during the innate response of zebrafish to trypanosome infections

A tightly regulated innate immune response to trypanosome infections is critical to strike a balance between parasite control and inflammation-associated pathology. In this study, we make use of the recently established Trypanosoma carassii infection model in larval zebrafish to study the early response of macrophages and neutrophils to trypanosome infections in vivo. We consistently identified high- and low-infected individuals and were able to simultaneously characterise their differential innate response. Not only did macrophage and neutrophil number and distribution differ between the two groups, but also macrophage morphology and activation state. Exclusive to high-infected zebrafish, was the occurrence of foamy macrophages characterised by a strong pro-inflammatory profile and potentially associated with an exacerbated immune response as well as susceptibility to the infection. To our knowledge, this is the first report of the occurrence of foamy macrophages during an extracellular trypanosome infection.

If it's not one thing, HIF's another: immunoregulation by hypoxia inducible factors in disease

Hypoxia‐inducible factors (HIFs) have emerged in recent years as critical regulators of immunity. Localised, low oxygen tension is a hallmark of inflamed and infected tissues. Subsequent myeloid cell HIF stabilisation plays key roles in the innate immune response, alongside emerging oxygen‐independent roles. Manipulation of regulatory proteins of the HIF transcription factor family can profoundly influence inflammatory profiles, innate immune cell function and pathogen clearance and, as such, has been proposed as a therapeutic strategy against inflammatory diseases. The direction and mode of HIF manipulation as a therapy are dictated by the inflammatory properties of the disease in question, with innate immune cell HIF reduction being, in general, advantageous during chronic inflammatory conditions, while upregulation of HIF is beneficial during infections. The therapeutic potential of targeting myeloid HIFs, both genetically and pharmacologically, has been recently illuminated in vitro and in vivo, with an emerging range of inhibitory and activating strategies becoming available. This review focuses on cutting edge findings that uncover the roles of myeloid cell HIF signalling on immunoregulation in the contexts of inflammation and infection and explores future directions of potential therapeutic strategies.

Visualizing trypanosomes in a vertebrate host reveals novel swimming behaviours, adaptations and attachment mechanisms

Trypanosomes are important disease agents of humans, livestock and cold-blooded species, including fish. The cellular morphology of trypanosomes is central to their motility, adaptation to the host’s environments and pathogenesis. However, visualizing the behaviour of trypanosomes resident in a live vertebrate host has remained unexplored. In this study, we describe an infection model of zebrafish (Danio rerio) with Trypanosoma carassii. By combining high spatio-temporal resolution microscopy with the transparency of live zebrafish, we describe in detail the swimming behaviour of trypanosomes in blood and tissues of a vertebrate host. Besides the conventional tumbling and directional swimming, T. carassii can change direction through a ‘whip-like’ motion or by swimming backward. Further, the posterior end can act as an anchoring site in vivo. To our knowledge, this is the first report of a vertebrate infection model that allows detailed imaging of trypanosome swimming behaviour in vivo in a natural host environment.

Trypanosomes are one-celled parasites that cause the disease trypanosomiasis, which is also known as sleeping sickness. Trypanosomiasis is transmitted to humans and animals by a type of fly, known as tse-tse, which is commonly found in sub-Saharan Africa. A bite from the tse-tse fly transfers the trypanosome cells into the host’s bloodstream, where they spread from the blood to the internal organs and brain. This leads to a long-term illness, which can sometimes result in a coma and eventually death.

Once in the blood trypanosomes move around using a structure similar to an underwater propeller called the flagellum. How the trypanosomes move and behave in the blood determines how the infection will progress. Until now it has only been possible to observe trypanosomes in plastic dishes or in blood drawn from infected patients. However, neither of these settings mimic the conditions of the bloodstream, and it is currently impossible to look inside human hosts to watch how trypanosomes move.

To overcome this hurdle, Doro et al. infected zebrafish with Trypanosoma carassii, a close relative of the sub-Saharan trypanosomes that specifically infects fish. Zebrafish are transparent when young, making it possible to observe the parasite in the blood and tissues of live fish using a microscope.

Doro et al. noticed that Trypanosoma carassii cells adapt to different environments in the host by using different swimming techniques. For example, in small capillaries trypanosomes were dragged along with the blood flow, whilst in larger vessels, when blood flow was slow or there were fewer red blood cells, trypanosomes actively swam against the current. The parasites were also able to change direction by using their flagella in a ‘whip-like’ motion. Lastly, it was discovered that Trypanosoma carassii could rapidly attach to blood vessel walls using one end of its cell body, even when blood flow was strong. This behaviour may help the parasites escape from the bloodstream into the surrounding tissues, making the infection more dangerous.

Studying how trypanosomes infect zebrafish at this high level of detail provides new insights into how these parasites move and behave inside a host. An important question that remains to be answered, is how exactly the trypanosomes leave the bloodstream. A better understanding of the whole infection process may hint at new ways of fighting these deadly infections in future.

Regulation and expression of human Fabs under the control of the Escherichia coli arabinose promoter, PBAD

BACKGROUND

The L-arabinose operon from E. coli contains an inducible promoter PBAD which has been extensively studied for the control of gene expression. PBAD has a number of potential advantages over Plac, and has been used successfully to promote high level expression of recombinant proteins.

OBJECTIVES

The aim of this study was to investigate PBAD as an alternative system to Plac for the bacterial expression of recombinant Fabs.

STUDY DESIGN

The promoter PBAD from the E. coli arabinose operon araBAD and the gene encoding the regulator of this promoter, were cloned into the phagemid expression vector MCO1. Expression of human recombinant tetanus toxoid (TT) and c-erbB2 Fabs under the control of PBAD was compared at two induction temperatures with the same Fabs produced under the control of Plac.

RESULTS

Expression of TT and c-erbB2 Fabs under the control of PBAD was comparable to Fab expression from Plac. However, highly expressed TT Fab under the control of PBAD was localised to the soluble periplasmic fraction whereas under the control of Plac, there was greater leakage of Fab into the culture supernatant. In addition, Fab expression from PBAD could be more tightly repressed than from Plac.

CONCLUSION

PBAD is a useful and cheaply inducible alternative to the more commonly used Plac for the rapid expression of soluble recombinant human antibody fragments.

Production of endometrial matrix metalloproteinases, but not their tissue inhibitors, is modulated by progesterone withdrawal in an in vitro model for menstruation

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are implicated in normal menstruation, but the mechanism of their regulation is not yet clear. Human endometrial stromal cell cultures were established to mimic the events of the late luteal phase of the menstrual cycle: after 6 days of culture with estradiol 17beta (10 nmol/L) and progestin (P, 100 nmol/L), half the cells were subjected to P withdrawal, and medium was harvested on day 10. Decidualization of the cells was verified by PRL immunohistochemistry. Latent MMP-1, -2, -3, and -9 were detected by zymography and quantitated by densitometry, and production of all enzymes was increased on withdrawal of P. This increase was confirmed by enzyme-linked immunosorbent assay for MMP-1. TIMP-1, -2, and -3 also were produced by the cells, with a mean ratio of 3.9:1:1.2, respectively. There was no effect of P withdrawal on either the amount of each TIMP or their relative concentrations. Expression of the messenger RNA for TIMP-1 or TIMP-2 also was not changed by P withdrawal. Thus, withdrawal of P alters the ratio of MMPs to TIMPs in this model in favor of MMPs and, hence, of tissue degradation. However, the focal nature of menstruation-associated MMP activity suggests that P withdrawal is unlikely to be the only factor responsible for in vivo induction of MMPs at menstruation.