Functional Analysis of Phagocyte Activity in Whole Blood from HIV/Tuberculosis-Infected Individuals Using a Novel Flow Cytometry-Based Assay

A review of pulmonary neutrophilia and insights into the key role of neutrophils in particle-induced pathogenesis in the lung from animal studies of lunar dusts and other poorly soluble dust particles

The mechanisms of particle-induced pathogenesis in the lung remain poorly understood. Neutrophilic inflammation and oxidative stress in the lung are hallmarks of toxicity. Some investigators have postulated that oxidative stress from particle surface reactive oxygen species (psROS) on the dust produces the toxicopathology in the lungs of dust-exposed animals. This postulate was tested concurrently with the studies to elucidate the toxicity of lunar dust (LD), which is believed to contain psROS due to high-speed micrometeoroid bombardment that fractured and pulverized lunar surface regolith. Results from studies of rats intratracheally instilled (ITI) with three LDs (prepared from an Apollo-14 lunar regolith), which differed 14-fold in levels of psROS, and two toxicity reference dusts (TiO2 and quartz) indicated that psROS had no significant contribution to the dusts' toxicity in the lung. Reported here are results of further investigations by the LD toxicity study team on the toxicological role of oxidants in alveolar neutrophils that were harvested from rats in the 5-dust ITI study and from rats that were exposed to airborne LD for 4 weeks. The oxidants per neutrophils and all neutrophils increased with dose, exposure time and dust's cytotoxicity. The results suggest that alveolar neutrophils play a critical role in particle-induced injury and toxicity in the lung of dust-exposed animals. Based on these results, we propose an adverse outcome pathway (AOP) for particle-associated lung disease that centers on the crucial role of alveolar neutrophil-derived oxidant species. A critical review of the toxicology literature on particle exposure and lung disease further supports a neutrophil-centric mechanism in the pathogenesis of lung disease and may explain previously reported animal species differences in responses to poorly soluble particles. Key findings from the toxicology literature indicate that (1) after exposures to the same dust at the same amount, rats have more alveolar neutrophils than hamsters; hamsters clear more particles from their lungs, consequently contributing to fewer neutrophils and less severe lung lesions; (2) rats exposed to nano-sized TiO2 have more neutrophils and more severe lesions in their lungs than rats exposed to the same mass-concentration of micron-sized TiO2; nano-sized dust has a greater number of particles and a larger total particle-cell contact surface area than the same mass of micron-sized dust, which triggers more alveolar epithelial cells (AECs) to synthesize and release more cytokines that recruit a greater number of neutrophils leading to more severe lesions. Thus, we postulate that, during chronic dust exposure, particle-inflicted AECs persistently release cytokines, which recruit neutrophils and activate them to produce oxidants resulting in a prolonged continuous source of endogenous oxidative stress that leads to lung toxicity. This neutrophil-driven lung pathogenesis explains why dust exposure induces more severe lesions in rats than hamsters; why, on a mass-dose basis, nano-sized dusts are more toxic than the micron-sized dusts; why lung lesions progress with time; and why dose-response curves of particle toxicity exhibit a hockey stick like shape with a threshold. The neutrophil centric AOP for particle-induced lung disease has implications for risk assessment of human exposures to dust particles and environmental particulate matter.

Practical considerations for a TB controlled human infection model (TB-CHIM); the case for TB-CHIM in Africa, a systematic review of the literature and report of 2 workshop discussions in UK and Malawi

Background: Tuberculosis (TB) remains a major challenge in many domains including diagnosis, pathogenesis, prevention, treatment, drug resistance and long-term protection of the public health by vaccination. A controlled human infection model (CHIM) could potentially facilitate breakthroughs in each of these domains but has so far been considered impossible owing to technical and safety concerns. Methods: A systematic review of mycobacterial human challenge studies was carried out to evaluate progress to date, best possible ways forward and challenges to be overcome. We searched MEDLINE (1946 to current) and CINAHL (1984 to current) databases; and Google Scholar to search citations in selected manuscripts. The final search was conducted 3 rd February 2022. Inclusion criteria: adults ≥18 years old; administration of live mycobacteria; and interventional trials or cohort studies with immune and/or microbiological endpoints. Exclusion criteria: animal studies; studies with no primary data; no administration of live mycobacteria; retrospective cohort studies; case-series; and case-reports. Relevant tools (Cochrane Collaboration for RCTs and Newcastle-Ottawa Scale for non-randomised studies) were used to assess risk of bias and present a narrative synthesis of our findings. Results: The search identified 1,388 titles for review; of these 90 were reviewed for inclusion; and 27 were included. Of these, 15 were randomised controlled trials and 12 were prospective cohort studies. We focussed on administration route, challenge agent and dose administered for data extraction. Overall, BCG studies including fluorescent BCG show the most immediate utility, and genetically modified Mycobacteria tuberculosis is the most tantalising prospect of discovery breakthrough. Conclusions: The TB-CHIM development group met in 2019 and 2022 to consider the results of the systematic review, to hear presentations from many of the senior authors whose work had been reviewed and to consider best ways forward. This paper reports both the systematic review and the deliberations. Registration: PROSPERO ( CRD42022302785; 21 January 2022).

Persistent changes in expression of genes involved in inflammation and fibrosis in the lungs of rats exposed to airborne lunar dust

NASA is currently planning return missions to the Moon for further exploration and research. The Moon is covered by a layer of potentially reactive fine dust, which could pose a toxicological risk of exposure to explorers. To assess this risk, we exposed rats to lunar dust (LD) that was collected during the Apollo14 mission. Rats were exposed to respirable sizes of LD at concentrations of 0, 2.1, 6.8, 20.8, or 60.6 mg/m³ for 4 weeks. One day, and one, four, and thirteen  weeks after exposure, we assessed 44,000 gene transcripts and found the expression of 614 genes with known functions were significantly altered in the rats exposed to the 2 higher concentrations of LD, whereas few changes in gene expression were detected in the group exposed to the lowest concentration of LD. Many of the significant changes in gene expression involved genes known to be associated with inflammation or fibrosis. Four genes encoding pro-inflammatory chemokines were analyzed further using real-time polymerase chain reaction. The expression of these genes was altered in a dose- and time-dependent manner and persistently changed in the lungs of the rats exposed to the two higher concentrations of LD. Their expressions are consistent with changes we detected in pulmonary toxicity biomarkers and pathology in these animals during a previous study. Because Apollo-14 LD contains common mineral oxides similar to an Arizona volcanic ash, besides revealing the toxicity of LD, our findings could help elucidate the genomic and molecular mechanisms involved in pulmonary toxicity induced by terrestrial mineral dusts.

Multiparametric Profiling of Neutrophil Function via a High-Throughput Flow Cytometry-Based Assay

Neutrophils are a vital component of the innate immune system and play an essential function in the recognition and clearance of bacterial and fungal pathogens. There is great interest in understanding mechanisms of neutrophil dysfunction in the setting of disease and deciphering potential side effects of immunomodulatory drugs on neutrophil function. We developed a high throughput flow cytometry-based assay for detecting changes to four canonical neutrophil functions following biological or chemical triggers. Our assay detects neutrophil phagocytosis, reactive oxygen species (ROS) generation, ectodomain shedding, and secondary granule release in a single reaction mixture. By selecting fluorescent markers with minimal spectral overlap, we merge four detection assays into one microtiter plate-based assay. We demonstrate the response to the fungal pathogen, Candida albicans and validate the assay's dynamic range using the inflammatory cytokines G-CSF, GM-CSF, TNFα, and IFNγ. All four cytokines increased ectodomain shedding and phagocytosis to a similar degree while GM-CSF and TNFα were more active in degranulation when compared to IFNγ and G-CSF. We further demonstrated the impact of small molecule inhibitors such as kinase inhibition downstream of Dectin-1, a critical lectin receptor responsible for fungal cell wall recognition. Bruton's tyrosine kinase (Btk), Spleen tyrosine kinase (Syk), and Src kinase inhibition suppressed all four measured neutrophil functions but all functions were restored with lipopolysaccharide co-stimulation. This new assay allows for multiple comparisons of effector functions and permits identification of distinct subpopulations of neutrophils with a spectrum of activity. Our assay also offers the potential for studying the intended and off-target effects of immunomodulatory drugs on neutrophil responses.

Practical considerations for a TB controlled human infection model (TB-CHIM); the case for TB-CHIM in Africa, a systematic review of the literature and report of 2 workshop discussions in UK and Malawi

Background: Tuberculosis (TB) remains a major challenge in many domains including diagnosis, pathogenesis, prevention, treatment, drug resistance and long-term protection of the public health by vaccination. A controlled human infection model (CHIM) could potentially facilitate breakthroughs in each of these domains but has so far been considered impossible owing to technical and safety concerns. Methods: A systematic review of mycobacterial human challenge studies was carried out to evaluate progress to date, best possible ways forward and challenges to be overcome. We searched MEDLINE (1946 to current) and CINAHL (1984 to current) databases; and Google Scholar to search citations in selected manuscripts. The final search was conducted 3 rd February 2022. Inclusion criteria: adults ≥18 years old; administration of live mycobacteria; and interventional trials or cohort studies with immune and/or microbiological endpoints. Exclusion criteria: animal studies; studies with no primary data; no administration of live mycobacteria; retrospective cohort studies; case-series; and case-reports. Relevant tools (Cochrane Collaboration for RCTs and Newcastle-Ottawa Scale for non-randomised studies) were used to assess risk of bias and present a narrative synthesis of our findings. Results: The search identified 1,388 titles for review; of these 90 were reviewed for inclusion; and 27 were included. Of these, 15 were randomised controlled trials and 12 were prospective cohort studies. We focussed on administration route, challenge agent and dose administered for data extraction. Overall, BCG studies including fluorescent BCG show the most immediate utility, and genetically modified Mycobacteria tuberculosis is the most tantalising prospect of discovery breakthrough. Conclusions: The TB-CHIM development group met in 2019 and 2022 to consider the results of the systematic review, to hear presentations from many of the senior authors whose work had been reviewed and to consider best ways forward. This paper reports both the systematic review and the deliberations. Registration: PROSPERO ( CRD42022302785; 21 January 2022).

Defective Monocyte Enzymatic Function and an Inhibitory Immune Phenotype in Human Immunodeficiency Virus-Exposed Uninfected African Infants in the Era of Antiretroviral Therapy

BACKGROUND

Human immunodeficiency virus-exposed uninfected (HEU) infants are a rapidly expanding population in sub-Saharan Africa and are highly susceptible to encapsulated bacterial disease in the first year of life. The mechanism of this increased risk is still poorly understood. We investigated whether human immunodeficiency virus (HIV)-exposure dysregulates HEU immunity, vaccine-antibody production, and human herpes virus amplify this effect.

METHODS

Thirty-four HIV-infected and 44 HIV-uninfected pregnant women were recruited into the birth cohort and observed up to 6 weeks of age; and then a subsequent 43 HIV-infected and 61 HIV-uninfected mother-infant pairs were recruited into a longitudinal infant cohort at either: 5-7 to 14-15; or 14-15 to 18-23 weeks of age. We compared monocyte function, innate and adaptive immune cell phenotype, and vaccine-induced antibody responses between HEU and HIV-unexposed uninfected (HU) infants.

RESULTS

We demonstrate (1) altered monocyte phagosomal function and B-cell subset homeostasis and (2) lower vaccine-induced anti-Haemophilus influenzae type b (Hib) and anti-tetanus toxoid immunoglobulin G titers in HEU compared with HU infants. Human herpes virus infection was similar between HEU and HU infants.

CONCLUSIONS

In the era of antiretroviral therapy-mediated viral suppression, HIV exposure may dysregulate monocyte and B-cell function, during the vulnerable period of immune maturation. This may contribute to the high rates of invasive bacterial disease and pneumonia in HEU infants.

Landscape and age dynamics of immune cells in the Egyptian rousette bat

Bats harbor high-impact zoonotic viruses often in the absence of disease manifestation. This restriction and disease tolerance possibly rely on specific immunological features. In-depth molecular characterization of cellular immunity and imprinting of age on leukocyte compartments remained unexplored in bats. We employ single-cell RNA sequencing (scRNA-seq) and establish immunostaining panels to characterize the immune cell landscape in juvenile, subadult, and adult Egyptian rousette bats (ERBs). Transcriptomic and flow cytometry data reveal conserved subsets and substantial enrichments of CD79a⁺ B cells and CD11b⁺ T cells in juvenile animals, whereas neutrophils, CD206⁺ myeloid cells, and CD3⁺ T cells dominate as bats reach adulthood. Despite differing frequencies, phagocytosis of circulating and tissue-resident myeloid cells and proliferation of peripheral and splenic lymphocytes are analogous in juvenile and adult ERBs. We provide a comprehensive map of the immune landscape in ERBs and show age-imprinted resilience progression and find that variability in cellular immunity only partly recapitulates mammalian archetypes.

Distinct behavior of bovine-associated staphylococci species in their ability to resist phagocytosis and trigger respiratory burst activity by blood and milk polymorphonuclear leukocytes in dairy cows

Mastitis affects a high proportion of dairy cows and is still one of the greatest challenges faced by the dairy industry. Staphylococcal bacteria remain the most important cause of mastitis worldwide. We investigated how distinct staphylococcal species evade some critical host defense mechanisms, which may dictate the establishment, severity, and persistence of infection and the outcome of possible therapeutic and prevention interventions. Thus, the present study investigated variations among distinct bovine-associated staphylococci in their capability to resist phagocytosis and to trigger respiratory burst activity of blood and milk polymorphonuclear neutrophil leukocytes (PMNL) in dairy cows. To do so, PMNL of 6 primiparous and 6 multiparous dairy cows were used. A collection of 38 non-aureus staphylococci (NAS) and 12 Staphylococcus aureus were included. The phagocytosis and intracellular reactive oxygen species (ROS) production by blood and milk PMNL were analyzed by flow cytometry. Phagocytosis, by both blood and milk PMNL, did not differ between S. aureus and NAS as a group, although within-NAS species differences were observed. Staphylococcus chromogenes (a so-called milk-adapted NAS species) better resisted phagocytosis by blood PMNL than the so-called environmental (i.e., Staphylococcus fleurettii) and opportunistic (i.e., Staphylococcus haemolyticus) NAS species. Otherwise, S. haemolyticus was better phagocytosed by blood PMNL than S. aureus, S. fleurettii, and S. chromogenes. No influence of the origin of the isolates within the staphylococci species in the resistance to phagocytosis by blood and milk PMNL was found. Overall, both S. aureus and NAS did not inhibit intracellular ROS production in blood and milk PMNL. Non-aureus staphylococci induced fewer ROS by milk PMNL than S. aureus, which was not true for blood PMNL, although species-specific differences in the intensity of ROS production were observed. Staphylococcus chromogenes induced more blood PMNL ROS than S. fleurettii and S. haemolyticus, and as much as S. aureus. Conversely, S. chromogenes induced fewer milk PMNL ROS than S. aureus. The origin of the isolates within the staphylococci species did not affect the ROS production by blood and milk PMNL. In conclusion, our study showed differences in staphylococci species in evading phagocytosis and triggering ROS production, which may explain the ability of some staphylococci species (i.e., S. aureus and S. chromogenes) to cause persistent infection and induce inflammation.

The whole blood phagocytosis assay: a clinically relevant test of neutrophil function and dysfunction in community-acquired pneumonia

Objective

To refine and validate a neutrophil function assay with clinical relevance for patients with community-acquired pneumonia (CAP).

Design

Two phase cross-sectional study to standardise and refine the assay in blood from healthy volunteers and test neutrophil phagocytic function in hospital patients with CAP.

Participants

Phase one: Healthy adult volunteers (n = 30). Phase two: Critical care patients with severe CAP (n = 16), ward-level patients with moderate CAP (n = 15) and respiratory outpatients (no acute disease, n = 15).

Results

Our full standard operating procedure for the assay is provided. Patients with severe CAP had significantly decreased neutrophil function compared to moderate severity disease (median phagocytic index 2.8 vs. 18.0, p = 0.014). Moderate severity pneumonia neutrophil function was significantly higher than control samples (median 18.0 vs. 1.6, p = 0.015). There was no significant difference between critical care and control neutrophil function (median 2.8 vs. 1.6, p = 0.752).

Conclusions

Our whole blood neutrophil assay is simple, reproducible and clinically relevant. Changes in neutrophil function measured in this pneumonia cohort is in agreement with previous studies. The assay has potential to be used to identify individuals for clinical trials of immunomodulatory therapies, to risk-stratify patients with pneumonia, and to refine our understanding of ‘normal’ neutrophil function in infection.

Defective Phagocytic Properties of HIV-Infected Macrophages: How Might They Be Implicated in the Development of Invasive Salmonella Typhimurium?

Human immunodeficiency virus type 1 (HIV-1) infects and kills T cells, profoundly damaging the host-specific immune response. The virus also integrates into memory T cells and long-lived macrophages, establishing chronic infections. HIV-1 infection impairs the functions of macrophages both in vivo and in vitro, which contributes to the development of opportunistic diseases. Non-typhoidal Salmonella enterica serovar Typhimurium has been identified as the most common cause of bacterial bloodstream infections in HIV-infected adults. In this review, we report how the functions of macrophages are impaired post HIV infection; introduce what makes invasive Salmonella Typhimurium specific for its pathogenesis; and finally, we discuss why these bacteria may be particularly adapted to the HIV-infected host.