Impacts of extreme climate on Australia's green cover (2003-2018): A MODIS and mascon probe

Australia as a continent represents a semi-arid environment that is generally water-limited. Changes in rainfall pattern will inevitably occur due to rising temperatures caused by climate change, which has a direct impact on the distribution of Australia's vegetation (green cover). As variability in rainfall continues to increase, i.e., in frequency and/or magnitude, due to climate change, extreme climate events such as droughts are predicted to become more pervasive and severe that will have an adverse effect on vegetation. This study investigates the effects of extreme climate on Australia's green cover during 2003-2018 for the end of rainy seasons of April and October in the northern and southern parts, respectively, to (i) determine the state of vegetation and its changes, (ii) identify "hotspots", i.e., regions that constantly experienced statistically significant decrease in NDVI, and (iii), relate changes in the identified hotspots to GRACE-hydrological changes. These are achieved through the exploitation of the statistical tools of Principal Component Analysis (PCA) and Mann-Kendel Test on Gravity Recovery and Climate Experiment (GRACE) hydrological products on the one hand, and the utilization of Australia's rainfall product and Moderate Resolution Imaging Spectroradiometer Normalized Difference Vegetation Index (MODIS-NDVI) used here with its native spatial resolution of 0.002413^∘ × 0.002413^∘ on the other hand. Differences between 3-year intervals from 2003 to 2018 for both April and October datasets are used to quantify vegetation variations. Through area change analysis, the vegetation differences (2003-2018) indicate that April exhibited larger increase (13.77% of total vegetation area) than decrease (7.83%) compared to October, which experienced slightly larger decrease (9.41%) than increase (8.71%). South Australia and Western Australia emerge as "hotspots" in which vegetation statistically decreased in October, with no noticeable change in April. GRACE-based hydrological changes in both hotspots reflect a decreasing trend (2003-2009) and increasing trend (2009-2012) that peaks in 2011, which then transitions towards a gradually decreasing trend after 2012. Australia-wide climate variability (ENSO and IOD) influenced vegetation variations during the data period 2003 to 2018.

Anakinra in hospitalized patients with severe COVID-19 pneumonia requiring oxygen therapy: Results of a prospective, open-label, interventional study

Objective

The aim of this study was to evaluate the efficacy of anakinra in patients who were admitted to hospital for severe COVID-19 pneumonia requiring oxygen therapy.

Methods

A prospective, open-label, interventional study in adults hospitalized with severe COVID-19 pneumonia was conducted. Patients in the interventional arm received subcutaneous anakinra (100 mg twice daily for 3 days, followed by 100 mg daily for 7 days) in addition to standard treatment. Main outcomes were the need for mechanical ventilation and in-hospital death. Secondary outcomes included successful weaning from supplemental oxygen and change in inflammatory biomarkers. Outcomes were compared with those of historical controls who had received standard treatment and supportive care.

Results

A total of 69 patients were included: 45 treated with anakinra and 24 historical controls. A need for mechanical ventilation occurred in 14 (31%) of the anakinra-treated group and 18 (75%) of the historical cohort (p < 0.001). In-hospital death occurred in 13 (29%) of the anakinra-treated group and 11 (46%) of the historical cohort (p = 0.082). Successful weaning from supplemental oxygen to ambient air was attained in 25 (63%) of the anakinra-treated group compared with 6 (27%) of the historical cohort (p = 0.008). Patients who received anakinra showed a significant reduction in inflammatory biomarkers.

Conclusion

In patients with severe COVID-19 pneumonia and high oxygen requirement, anakinra could represent an effective treatment option and may confer clinical benefit.

Trial registration number

ISRCTN74727214.

Endocrinological Abnormalities and Growth Impairment in Human Immunodeficiency Virus-Infected Children

Background Pediatric human immunodeficiency virus (HIV) is an important emerging disease and many children are surviving into adulthood with effective antiretroviral therapy. Growth dysregulation is common in these children and endocrine abnormalities are likely to be a possible comorbidity. There is a paucity of data on these endocrinological abnormalities in this population. Against this background, a study to evaluate the endocrinological profile in HIV-infected children and its relationship with growth failure was performed.

Methods A cross-sectional descriptive study was performed in children less than 18 years attending the pediatric HIV clinic at a tertiary care hospital in central India. Blood samples for T3, T4, thyroid-stimulating hormone (TSH), growth hormone (GH), dehydroepiandrosterone (DHEA), cortisol, and insulin-like growth factor-binding protein 3 (IGFBP3) were collected during routine visit, preserved at –70°C, and subsequently assayed. Statistical analysis for the data with respect to the endocrinological abnormalities and growth failure was performed.

Results A total of 100 children were included in the study. The prevalence of growth failure was high. Nineteen percent children had height less than − 3 standard deviation (SD) and 59% children had height less than 2SD. The prevalence of endocrinological abnormalities was also high. Fifty-four percent children had low T3 levels, 12% had low T4 levels, 4% had high TSH levels, 44% had low cortisol levels, and 25% had low DHEA. Fifty-eight percent children had low GH levels, while IGFBP3 levels were low in the entire cohort. There was a statistically significant association between growth failure and levels of T3 and GH.

Conclusion Our results show a high prevalence of growth failure and endocrinological abnormalities in HIV-infected children. A significant association between growth failure and endocrine abnormalities was found for T3 and GH.

Prevalence, predictors and challenges of gestational diabetes mellitus screening among pregnant women in northern Tanzania

OBJECTIVES

To determine the prevalence and predictors of gestational diabetes mellitus (GDM) as well as acceptability of returning for glucose tolerance testing among pregnant women in Moshi municipality, northern Tanzania.

METHODS

Cross-sectional study from October 2015 to April 2016 among women with gestation age of 24-28 weeks of pregnancy attending at Kilimanjaro Christian Medical Centre (KCMC) referral hospital, Majengo and Pasua Health Centres. Women were interviewed and requested to return the next day (window within a month, depending on gestational age) for fasting plasma glucose (FPG) testing, followed immediately by a 75 g oral glucose tolerance test (OGTT). GDM was diagnosed using the 2013 WHO criteria. Logistic regression was conducted to reveal independent predictors for GDM.

RESULTS

Of 433 interviewed women, 100 (23%) did not return for FPG and OGTT testing. The prevalence of GDM among the 333 screened women was 19.5%, and 3% had diabetes in pregnancy (DIP). GDM was significantly associated with age ≥35 years (adjusted OR 6.75), pre-pregnancy obesity (AOR 2.22) and history of abortion (AOR 2.36).

CONCLUSION

Prevalence of GDM is high in Moshi. We recommend introduction of routine screening for hyperglycaemia during pregnancy along with strategies for follow-up to prevent long-term effects of GDM and DIP in women and their children.

Chest wall lymphomas: Fine needle aspiration cytodiagnosis and review of the literature

OBJECTIVE

Compared to other chest wall malignancies, lymphoma is a common disease. However, published literature on a series of lymphoma cases involving the chest wall is scarce. The aim of the present study, was to describe experience with chest wall swellings diagnosed as lymphoid neoplasms on fine needle aspiration (FNA) cytology.

METHODS

Eleven chest wall swellings were diagnosed as lymphoid neoplasms on FNA over a period of 15 years (January 2000-December 2014). The age of patients ranged from 19 to 73 years (median, 46). The male-to -emale ratio was 7:4. Ten cases had an anterior or lateral chest wall mass, and one swelling was in the scapular region. Six cases had concurrent lymphadenopathy, and one had bone involvement. The FNA smears were reviewed and classified under WHO Classification of Hematopoietic Neoplasms. The histopathological diagnoses were available in eight cases.

RESULTS

The preliminary cytodiagnoses in 11 cases of chest wall lymphoid neoplasms were anaplastic large cell lymphoma (ALCL) in two cases, and ALCL/malignant melanoma, ALCL/T-cell-rich-B-cell lymphoma (TCRBCL)/Hodgkin's lymphoma (HL), plasmacytoma/neuroendocrine carcinoma, Hodgkin's lymphoma, small cell NHL/CLL, NHL, suggestive of NHL, post-transplant peripheral T-cell lymphoma (PTCL), and a malignant plasma cell tumour in one case each. The reviewed cytodiagnoses of lymphoid neoplasms were as follows: ALCL ( five cases), centroblastic lymphoma (two cases), and small cell lymphoma/CLL, post-transplant peripheral T-cell lymphoma, Hodgkin's lymphoma and plasmacytoma (one case each). Histopathological diagnoses available in eight cases confirmed the presence of lymphoid neoplasms.

CONCLUSION

A variety of lymphoid neoplasms involved the chest wall, and among them, ALCL was a common form.

CD11c-Expressing Cells Affect Regulatory T Cell Behavior in the Meninges during Central Nervous System Infection

Regulatory T cells (Tregs) play an important role in the CNS during multiple infections, as well as autoimmune inflammation, but the behavior of this cell type in the CNS has not been explored. In mice, infection with Toxoplasma gondii leads to a Th1-polarized parasite-specific effector T cell response in the brain. Similarly, Tregs in the CNS during T. gondii infection are Th1 polarized, as exemplified by their T-bet, CXCR3, and IFN-γ expression. Unlike effector CD4⁺ T cells, an MHC class II tetramer reagent specific for T. gondii did not recognize Tregs isolated from the CNS. Likewise, TCR sequencing revealed minimal overlap in TCR sequence between effector T cells and Tregs in the CNS. Whereas effector T cells are found in the brain parenchyma where parasites are present, Tregs were restricted to the meninges and perivascular spaces. The use of intravital imaging revealed that activated CD4⁺ T cells within the meninges were highly migratory, whereas Tregs moved more slowly and were found in close association with CD11c⁺ cells. To test whether the behavior of Tregs in the meninges is influenced by interactions with CD11c⁺ cells, mice were treated with anti-LFA-1 Abs to reduce the number of CD11c⁺ cells in this space. The anti-LFA-1 treatment led to fewer contacts between Tregs and the remaining CD11c⁺ cells and increased the speed of Treg migration. These data suggest that Tregs are anatomically restricted within the CNS, and their interaction with CD11c⁺ populations regulates their local behavior during T. gondii infection.

TLR4-Dependent Secretion by Hepatic Stellate Cells of the Neutrophil-Chemoattractant CXCL1 Mediates Liver Response to Gut Microbiota

Background & Aims

The gut microbiota significantly influences hepatic immunity. Little is known on the precise mechanism by which liver cells mediate recognition of gut microbes at steady state. Here we tested the hypothesis that a specific liver cell population was the sensor and we aimed at deciphering the mechanism by which the activation of TLR4 pathway would mediate liver response to gut microbiota.

Methods

Using microarrays, we compared total liver gene expression in WT versus TLR4 deficient mice. We performed in situ localization of the major candidate protein, CXCL1. With an innovative technique based on cell sorting, we harvested enriched fractions of KCs, LSECs and HSCs from the same liver. The cytokine secretion profile was quantified in response to low levels of LPS (1ng/mL). Chemotactic activity of stellate cell-derived CXCL1 was assayed in vitro on neutrophils upon TLR4 activation.

Results

TLR4 deficient liver had reduced levels of one unique chemokine, CXCL1 and subsequent decreased of neutrophil counts. Depletion of gut microbiota mimicked TLR4 deficient phenotype, i.e., decreased neutrophils counts in the liver. All liver cells were responsive to low levels of LPS, but hepatic stellate cells were the major source of chemotactic levels of CXCL1. Neutrophil migration towards secretory hepatic stellate cells required the TLR4 dependent secretion of CXCL1.

Conclusions

Showing the specific activation of TLR4 and the secretion of one major functional chemokine—CXCL1, the homolog of human IL-8-, we elucidate a new mechanism in which Hepatic Stellate Cells play a central role in the recognition of gut microbes by the liver at steady state.

Diverse roles for T-bet in the effector responses required for resistance to infection

The transcription factor T-bet has been most prominently linked to NK and T cell production of IFN-γ, a cytokine required for the control of a diverse array of intracellular pathogens. Indeed, in mice challenged with the parasite Toxoplasma gondii, NK and T cell responses are characterized by marked increases of T-bet expression. Unexpectedly, T-bet(-/-) mice infected with T. gondii develop a strong NK cell IFN-γ response that controls parasite replication at the challenge site, but display high parasite burdens at secondary sites colonized by T. gondii and succumb to infection. The loss of T-bet had a modest effect on T cell production of IFN-γ but did not impact on the generation of parasite-specific T cells. However, the absence of T-bet resulted in lower T cell expression of CD11a, Ly6C, KLRG-1, and CXCR3 and fewer parasite-specific T cells at secondary sites of infection, associated with a defect in parasite control at these sites. Together, these data highlight T-bet-independent pathways to IFN-γ production and reveal a novel role for this transcription factor in coordinating the T cell responses necessary to control this infection in peripheral tissues.

Improved delivery of the OVA-CD4 peptide to T helper cells by polymeric surface display on Salmonella

Background

Autotransporter proteins represent a treasure trove for molecular engineers who modify Gram-negative bacteria for the export or secretion of foreign proteins across two membrane barriers. A particularly promising direction is the development of autotransporters as antigen display or secretion systems. Immunologists have been using ovalbumin as a reporter antigen for years and have developed sophisticated tools to detect specific T cells that respond to ovalbumin. Although ovalbumin-expressing bacteria are being used to trace T cell responses to colonizing or invading pathogens, current constructs for ovalbumin presentation have not been optimized.

Results

The activation of T helper cells in response to ovalbumin was improved by displaying the OVA-CD4 reporter epitope as a multimer on the surface of Salmonella and fused to the autotransporter MisL. Expression was optimized by including tandem in vivo promoters and two post-segregational killing systems for plasmid stabilization.

Conclusions

The use of an autotransporter protein to present relevant epitope repeats on the surface of bacteria, combined with additional techniques favoring stable and efficient in vivo transcription, optimizes antigen presentation to T cells. The technique of multimeric epitope surface display should also benefit the development of new Salmonella or other enterobacterial vaccines.

The aryl hydrocarbon receptor promotes IL-10 production by NK cells

The cytokine IL-10 has an important role in limiting inflammation in many settings, including toxoplasmosis. In the present studies, an IL-10 reporter mouse was used to identify the sources of this cytokine following challenge with Toxoplasma gondii. During infection, multiple cell types expressed the IL-10 reporter but NK cells were a major early source of this cytokine. These IL-10 reporter(+) NK cells expressed high levels of the IL-12 target genes T-bet, KLRG1, and IFN-γ, and IL-12 depletion abrogated reporter expression. However, IL-12 signaling alone was not sufficient to promote NK cell IL-10, and activation of the aryl hydrocarbon receptor (AHR) was also required for maximal IL-10 production. NK cells basally expressed the AHR, relevant chaperone proteins, and the AHR nuclear translocator, which heterodimerizes with the AHR to form a competent transcription factor. In vitro studies revealed that IL-12 stimulation increased NK cell AHR levels, and the AHR and AHR nuclear translocator were required for optimal production of IL-10. Additionally, NK cells isolated from T. gondii-infected Ahr(-/-) mice had impaired expression of IL-10, which was associated with increased resistance to this infection. Taken together, these data identify the AHR as a critical cofactor involved in NK cell production of IL-10.

The cytokines interleukin 27 and interferon-γ promote distinct Treg cell populations required to limit infection-induced pathology

Interferon-γ (IFN-γ) promotes a population of T-bet(+) CXCR3(+) regulatory T (Treg) cells that limit T helper 1 (Th1) cell-mediated pathology. Our studies demonstrate that interleukin-27 (IL-27) also promoted expression of T-bet and CXCR3 in Treg cells. During infection with Toxoplasma gondii, a similar population emerged that limited T cell responses and was dependent on IFN-γ in the periphery but on IL-27 at mucosal sites. Transfer of Treg cells ameliorated the infection-induced pathology observed in Il27(-/-) mice, and this was dependent on their ability to produce IL-10. Microarray analysis revealed that Treg cells exposed to either IFN-γ or IL-27 have distinct transcriptional profiles. Thus, IFN-γ and IL-27 have different roles in Treg cell biology and IL-27 is a key cytokine that promotes the development of Treg cells specialized to control Th1 cell-mediated immunity at local sites of inflammation.

Generalized Lévy walks and the role of chemokines in migration of effector CD8+ T cells

Chemokines play a central role in regulating processes essential to the immune function of T cells^1-3, such as their migration within lymphoid tissues and targeting of pathogens in sites of inflammation. Here we track T cells using multi-photon microscopy to demonstrate that the chemokine CXCL10 enhances the ability of CD8⁺ T cells to control the pathogen T. gondii in the brains of chronically infected mice. This chemokine boosts T cell function in two different ways: it maintains the effector T cell population in the brain and speeds up the average migration speed without changing the nature of the walk statistics. Remarkably, these statistics are not Brownian; rather, CD8⁺ T cell motility in the brain is well described by a generalized Lévy walk. According to our model, this surprising feature enables T cells to find rare targets with more than an order of magnitude more efficiency than Brownian random walkers. Thus, CD8⁺ T cell behavior is similar to Lévy strategies reported in organisms ranging from mussels to marine predators and monkeys^4-10, and CXCL10 aids T cells in shortening the average time to find rare targets.

Validation of the Roche AMPLICOR HIV DNA test version 1.5 for early infant diagnosis of HIV in Papua New Guinea

Human immunodeficiency virus (HIV) is a significant public health issue in Papua New Guinea (PNG). After heterosexual transmission (90%), the second most common route of transmission is vertically from mother to child (3.5%). Before the introduction of molecular methods of HIV testing in PNG, diagnosing exposed infants was problematic because there were no reliable assays available for accurate early infant HIV detection. This study aimed to validate and assess a global gold standard for virological early infant HIV diagnosis in PNG: the AMPLICOR HIV DNA v1.5 assay (Roche) using dried blood spot (DBS) specimens. The assay was validated in three ways: by testing well-characterized DBS and kit controls and by blinded retesting of 42 patient specimens. The assay was further investigated by comparison with a serological assay. The results indicated that the assay was robust and highly reproducible using DBS and kit controls, with 100% sensitivity and specificity. Of the 42 infant DBS specimens that were retested blindly, 100% of the test results were concordant with diagnostic results. Among the 42 infant specimens tested with the Amplicor HIV DNA v1.5 assay we found that 33% of infants (n = 14) were HIV PCR positive and 67% (n = 28) negative. The earliest point of HIV detection established for this study was three months of age. This pilot study indicates that HIV-infected infants in PNG can be effectively diagnosed using virological testing and can thus be started earlier on treatment than was previously possible with serological testing.

Analysis of behavior and trafficking of dendritic cells within the brain during toxoplasmic encephalitis

Under normal conditions the immune system has limited access to the brain; however, during toxoplasmic encephalitis (TE), large numbers of T cells and APCs accumulate within this site. A combination of real time imaging, transgenic reporter mice, and recombinant parasites allowed a comprehensive analysis of CD11c⁺ cells during TE. These studies reveal that the CNS CD11c⁺ cells consist of a mixture of microglia and dendritic cells (DCs) with distinct behavior associated with their ability to interact with parasites or effector T cells. The CNS DCs upregulated several chemokine receptors during TE, but none of these individual receptors tested was required for migration of DCs into the brain. However, this process was pertussis toxin sensitive and dependent on the integrin LFA-1, suggesting that the synergistic effect of signaling through multiple chemokine receptors, possibly leading to changes in the affinity of LFA-1, is involved in the recruitment/retention of DCs to the CNS and thus provides new insights into how the immune system accesses this unique site.

Toxoplasmic encephalitis (TE), caused by the protozoan parasite Toxoplasma gondii, can be potentially life threatening especially in immuno-compromised individuals. Immune cells including dendritic cells have been shown to accumulate in the brain during chronic toxoplasmosis; however, little is known about their function, their behavior in vivo, and the mechanisms by which they migrate into the brain. In the present studies, we utilize a combination of real time imaging, transgenic reporter mice, and recombinant parasites to reveal the distinct behavior and morphologies of dendritic cells within the brain and their ability to interact with parasites and effector T cells during TE. The CNS DCs were also found to exhibit a unique chemokine receptor expression pattern during infection, and the migration of DCs into the brain was mediated through a pertussis toxin (which blocks signaling downstream of several chemokine receptors) sensitive process and dependent on the integrin LFA-1. There is currently a poor understanding of the events that lead to DC recruitment to the CNS during inflammation in general, and our studies provide new insights into the mechanisms by which antigen-presenting cells gain access to the brain during infection.

Evaluation of an electrostatic dust removal system with potential application in next-step fusion devices

The ability to manage inventories of carbon, tritium, and high-Z elements in fusion plasmas depends on means for effective dust removal. A dust conveyor, based on a moving electrostatic potential well, was tested with particles of tungsten, carbon, glass, and sand. A digital microscope imaged a representative portion of the conveyor, and dust particle size and volume distributions were derived before and after operation. About 10 mm(3) volume of carbon and tungsten particles were moved in under 5 s. The highest driving amplitude tested of 3 kV was the most effective. The optimal driving frequency was 210 Hz (maximum tested) for tungsten particles, decreasing to below 60 Hz for the larger sand particles. Measurements of particle size and volume distributions after 10 and 100 cycles show the breaking apart of agglomerated carbon and the change in particle distribution over short timescales (<1 s).

Advances in imaging the innate and adaptive immune response to Toxoplasma gondii

Toxoplasma gondii is an intracellular protozoan parasite that infects a wide variety of warm-blooded hosts and can have devastating effects in the developing fetus as well as the immunocompromised host. An appreciation of how this organism interacts with the host immune system is crucial to understanding the pathogenesis of this disease. The last decade has been marked by the application of various imaging techniques, such as bioluminescent imaging as well as confocal and multiphoton microscopy to study toxoplasmosis. The ability to manipulate parasites to express fluorescent/bioluminescent markers or model antigens/enzymes combined with the development of reporter mice that allow the detection of distinct immune populations have been crucial to the success of many of these studies. These approaches have permitted the visualization of parasites and immune cells in real-time and provided new insights into the nature of host-pathogen interactions. This article highlights some of the advances in imaging techniques, their strengths and weaknesses, and how these techniques have impacted our understanding of the interaction between parasites and various immune populations during toxoplasmosis.

Dendritic cells distinguish individual chemokine signals through CCR7 and CXCR4

Dendritic cells (DCs) respond to chemotactic signals to migrate from sites of infection to secondary lymphoid organs where they initiate the adaptive immune response. The key chemokines directing their migration are CCL19, CCL21, and CXCL12, but how signals from these chemokines are integrated by migrating cells is poorly understood. Using a microfluidic device, we presented single and competing chemokine gradients to murine bone-marrow derived DCs in a controlled, time-invariant microenvironment. Experiments performed with counter-gradients revealed that CCL19 is 10-100-fold more potent than CCL21 or CXCL12. Interestingly, when the chemoattractive potencies of opposing gradients are matched, cells home to a central region in which the signals from multiple chemokines are balanced; in this region, cells are motile but display no net displacement. Actin and myosin inhibitors affected the speed of crawling but not directed motion, whereas pertussis toxin inhibited directed motion but not speed. These results provide fundamental insight into the processes that DCs use to migrate toward and position themselves within secondary lymphoid organs.

Evidence-based management of heart failure in clinical practice: a review of device-based therapy use

BACKGROUND

Heart failure is a growing health issue and is associated with significant mortality risk. Device therapy is efficacious in preventing sudden death in patients with heart failure; however, this evidence comes from rigorous clinical trials. It is unclear how device therapy is utilized in 'real-world' practice. The primary objective was to characterize patterns of device use in patients with heart failure at risk of sudden death and to identify barriers to guideline-driven prescription of implantable cardioverter-defibrillators.

METHODS

We report a cross-sectional study of patients attending general cardiology clinic over a 3-month period.

RESULTS

Of 1003 consecutive patients attending the cardiology clinic, 176 had heart failure. Of these, 66 were potentially eligible for device therapy, but only 16 of these had actually undergone device implantation. Potentially eligible non-recipients were older (P < 0.001), more likely to have ischaemic cardiomyopathy (P= 0.002), less likely to be prescribed spironolactone (P= 0.005) or warfarin (P= 0.02), and less likely to have a widened QRS > 120 ms (P= 0.005). There was a high prevalence of underuse of evidence-based pharmacotherapies among patients with heart failure.

CONCLUSION

There is substantial underuse of device therapy in patients with heart failure. Strikingly, whereas patients with symptoms of heart failure were more likely to receive a device, those being managed for ischaemic heart disease were not. There is also a high prevalence of failure to prescribe evidence-based pharmacotherapy in a tertiary hospital general cardiology clinic. This may be explained in part by the lack of a patient database to record treatment contraindications and to alert clinicians to possible gaps in patient therapy.

Behavior and function of CD11c+ cells within the brain during chronic Toxoplasmosis (44.8)

Under normal conditions the brain is an immune-privileged site, however during toxoplasmic encephalitis (TE), there is significant increase in the proportion of T cells and antigen presenting cells (APCs) within the brain. Using a combination of real time imaging techniques, transgenic reporter mice, and recombinant parasites, the current studies have characterized the in vivo phenotype and function of CD11c+ cells present within the brain during this infection. These approaches have revealed the presence of an extensive network consisting of microglia and dendritic cells (including myeloid, lymphoid and plasmacytoid subsets) during TE. The CNS resident CD11c+ cells are functional APCs, as revealed by their ability to stimulate naïve antigen specific T cells in vitro. Further, real time imaging studies showed that these cells interacted with antigen specific T cells (for short durations) suggesting in vivo antigen presentation capabilities. The present studies have also identified a distinct chemokine receptor expression pattern on CD11c+ cells isolated from the brain, suggesting the importance of these receptors in trafficking of these cells into the inflamed brain. Using an adoptive transfer system, we show that the migration of DCs into the brain is Pertussis toxin sensitive. This latter model provides an opportunity to define the chemokine receptors responsible for the recruitment and retention of DCs in the brain.

Dynamic Imaging of CD8(+) T cells and dendritic cells during infection with Toxoplasma gondii

To better understand the initiation of CD8⁺ T cell responses during infection, the primary response to the intracellular parasite Toxoplasma gondii was characterized using 2-photon microscopy combined with an experimental system that allowed visualization of dendritic cells (DCs) and parasite specific CD8⁺ T cells. Infection with T. gondii induced localization of both these populations to the sub-capsular/interfollicular region of the draining lymph node and DCs were required for the expansion of the T cells. Consistent with current models, in the presence of cognate antigen, the average velocity of CD8⁺ T cells decreased. Unexpectedly, infection also resulted in modulation of the behavior of non-parasite specific T cells. This TCR-independent process correlated with the re-modeling of the lymph node micro-architecture and changes in expression of CCL21 and CCL3. Infection also resulted in sustained interactions between the DCs and CD8⁺ T cells that were visualized only in the presence of cognate antigen and were limited to an early phase in the response. Infected DCs were rare within the lymph node during this time frame; however, DCs presenting the cognate antigen were detected. Together, these data provide novel insights into the earliest interaction between DCs and CD8⁺ T cells and suggest that cross presentation by bystander DCs rather than infected DCs is an important route of antigen presentation during toxoplasmosis.

Toxoplasma gondii is a protozoan parasite that can infect a wide range of hosts, including humans. Infection with T. gondii is potentially life threatening in immuno-compromised individuals and it can be detrimental during pregnancy, often leading to abortion of the fetus. Dendritic cells are thought to play a vital role in the development of protective immunity to Toxoplasma gondii through their ability to produce immunological signals such as cytokines and also process and present parasite derived peptides to T cells. However, little is known about the actual interactions between these cell types in an intact organ, such as the lymph node, during infection. Using the technology of live imaging by 2-photon microscopy we have identified a very early window of time during infection when dendritic cells and T cells make sustained contacts with one another, which appears crucial for the generation of protective responses. We also show that substantial changes are induced in the lymph node micro-architecture as a result of infection, which in turn could have effects on immune responses to secondary pathogens. Understanding the interaction between these immune cells in vivo that leads to resistance to active infection would help in the design of better strategies to develop protective immune responses against this pathogen in immuno-compromised individuals.

Behavior of parasite-specific effector CD8+ T cells in the brain and visualization of a kinesis-associated system of reticular fibers

To understand lymphocyte behavior in the brain, we used two-photon microscopy to visualize effector CD8(+) T cells during toxoplasmic encephalitis. These cells displayed multiple behaviors with two distinct populations of cells apparent: one with a constrained pattern of migration and one with a highly migratory subset. The proportion of these populations varied over time associated with changes in antigen availability as well as T cell expression of the inhibitory receptor PD1. Unexpectedly, the movement of infiltrating cells was closely associated with an infection-induced reticular system of fibers. This observation suggests that, whereas in other tissues pre-existing scaffolds exist that guide lymphocyte migration, in the brain specialized structures are induced by inflammation that guide migration of T cells in this immune-privileged environment.