Properties of human blood monocytes. II. Monocytes from healthy adults are highly heterogeneous within and among individuals

Human monocyte subtype expression of neuroinflammation and regeneration-related genes is linked to age and sex

Stroke is a leading cause of disability and the third cause of death. The immune system plays an essential role in post-stroke recovery. After an ischemic stroke, monocytes infiltrate the injured brain tissue and can exacerbate or mitigate the damage. Ischemic stroke is more prevalent in the aged population, and the aging brain exhibits an altered immune response. There are also sex disparities in ischemic stroke incidence, outcomes, and recovery, and these differences may be hormone-driven and determined by genetic and epigenetic factors. Here, we studied whether human peripheral blood monocyte subtype (classical, intermediate, and non-classical) expression of neuronal inflammation- and regeneration-related genes depends on age and sex. A FACS analysis of blood samples from 44 volunteers (male and female, aged 28 to 98) showed that in contrast to other immune cells, the proportion of natural killer cells increased in females. The proportion of B-cells decreased in both sexes with age, and subtypes of monocytes were not linked to age or sex. Gene expression analysis by qPCR identified several genes differentially correlating with age and sex within different monocyte subtypes. Interestingly, ANXA1 and CD36 showed a consistent increase with aging in all monocytes, specifically in intermediate (CD36) and intermediate and non-classical (ANXA1) subtypes. Other genes (IL-1β, S100A8, TNFα, CD64, CD33, TGFβ1, TLR8, CD91) were differentially changed in monocyte subtypes with increased aging. Most age-dependent gene changes were differentially expressed in female monocytes. Our data shed light on the nuanced interplay of age and sex in shaping the expression of inflammation- and regeneration-related genes within distinct monocyte subtypes. Understanding these dynamics could pave the way for targeted interventions and personalized approaches in post-stroke care, particularly for the aging population and individuals of different sexes.

Assessment of inter-operator variability in peripheral monocyte subset gating strategy using flow cytometry in patients with suspected acute stroke

BACKGROUND

Innovative tools to reliably identify patients with acute stroke are needed. Peripheral monocyte subsets, that is, classical-Mon1, intermediate-Mon2, and non-classical-Mon3, with their activation marker expression analyzed using flow-cytometry (FCM) could be interesting cell biomarker candidates.

AIM

To assess the inter-operator variability in a new peripheral monocyte subset gating strategy using FCM in patients with suspected acute stroke.

METHODS

In BOOST-study ("Biomarkers-algOrithm-for-strOke-diagnoSis-and Treatment-resistance-prediction," NCT04726839), patients ≥18 years with symptoms suggesting acute stroke within the last 24 h were included. Blood was collected upon admission to emergency unit. FCM analysis was performed using the FACS-CANTO-II® flow-cytometer and Flow-Jo™-software. Analyzed markers were CD45/CD91/CD14/CD16 (monocyte backbone) and CD62L/CD11b/HLA-DR/CD86/CCR2/ICAM-1/CX3CR1/TF (activation markers). Inter-operator agreement (starting from raw-data files) was quantified by the measure distribution and, for each patient, the coefficient of variation (CV).

RESULTS

Three operators analyzed 20 patient blood samples. Median inter-operator CVs were below the pre-specified tolerance limits (10% [for Mon1 counts], 20% [Mon2, Mon3 counts], 15% [activation marker median-fluorescence-intensities]). We observed a slight, but systematic, inter-operator effect. Overall, absolute inter-operator differences in fractions of monocyte subsets were <0.03.

CONCLUSION

Our gating strategy allowed monocyte subset gating with an acceptable inter-operator variability. Although low, the inter-operator effect should be considered in monocyte data analysis of BOOST-patients.

CD163 as a Potential Biomarker of Monocyte Activation in Ischemic Stroke Patients

In ischemic stroke patients, a higher monocyte count is associated with disease severity and worse prognosis. The complex correlation between subset phenotypes and functions underscores the importance of clarifying the role of monocyte subpopulations. We examined the subtype-specific distribution of the CD163+ and CD80+ circulating monocytes and evaluated their association with the inflammatory status in 26 ischemic stroke patients and 16 healthy controls. An increased percentage of CD163+/CD16+ and CD163+/CD14++ events occurred 24 and 48 h after a stroke compared to the controls. CD163+ expression was more pronounced in CD16+ non-classical and intermediate monocytes, as compared to CD14+ classical subtype, 24 h after stroke. Conversely, the percentage of CD80+/CD16+ events was unaffected in patients; meanwhile, the percentage of CD80+/CD14+ events significantly increased only 24 h after stroke. Interleukin (IL)-1beta, TNF-alpha, and IL-4 mRNA levels were higher, while IL-10 mRNA levels were reduced in total monocytes from patients versus controls, at either 24 h or 48 h after stroke. The percentage of CD163+/CD16+ events 24 h after stroke was positively associated with NIHSS score and mRS at admission, suggesting that stroke severity and disability are relevant triggers for CD163+ expression in circulating CD16+ monocytes.

Identification of Novel Human Monocyte Subsets and Evidence for Phenotypic Groups Defined by Interindividual Variations of Expression of Adhesion Molecules

Monocytes contribute to immune responses as a source for subsets of dendritic cells and macrophages. Human blood monocytes are classified as classical, non-classical and intermediate cells. However, the particular functions of these subsets have been hard to define, with conflicting results and significant overlaps. One likely reason for these ambiguities is in the heterogeneity of these monocyte subsets regrouping cells with divergent functions. To better define monocyte populations, we have analysed expression of 17 markers by multicolour flow cytometry in samples obtained from 28 control donors. Data acquisition was tailored to detect populations present at low frequencies. Our results reveal the existence of novel monocyte subsets detected as larger CD14⁺ cells that were CD16⁺ or CD16^neg. These large monocytes differed from regular, smaller monocytes with respect to expression of various cell surface molecules, such as FcR, chemokine receptors, and adhesion molecules. Unsupervised multidimensional analysis confirmed the existence of large monocytes and revealed interindividual variations that were grouped according to unique patterns of expression of adhesion molecules CD62L, CD49d, and CD43. Distinct inflammatory responses to TLR agonists were found in small and large monocytes. Overall, refining the definition of monocyte subsets should lead to the identification of populations with specific functions.

Age-related M1/M2 phenotype changes in circulating monocytes from healthy/unhealthy individuals

Macrophage polarization is a candidate biomarker of disease-related inflammatory status, but its modulation during aging has not been investigated. To do this, the M1/M2 profile was assessed by CD80/CD163 gating in classical (CD14⁺⁺CD16^-), intermediate (CD14⁺⁺CD16⁺), and non-classical (CD14^lowCD16⁺) monocytes from 31 healthy subjects (CTRs) of different ages. Cytofluorimetric analysis showed a significantly different CD80/CD163 distribution in the three subsets, as more than 80% of classical and intermediate monocytes were CD80⁺CD163⁺, whereas most non-classical monocytes were CD80^-CD163^- and CD163⁺. Non-classical CD163⁺ monocytes were significantly higher whereas classical CD163⁺ and CD80^-CD163^- monocytes significantly lower in older than younger CTRs (cut-off, 65 years), suggesting different age-related trends for M2 subsets. To establish whether an M1/M2 imbalance could be associated with disease, 21 patients with acute myocardial infarction (AMI) were compared with older CTRs. The AMI patients showed a significantly decreased proportion of CD163⁺CD80⁺ and an increased proportion of CD163⁺ and CD163^-CD80^- cells among classical monocytes, opposite trends to those observed in healthy aging. Moreover, a significantly greater proportion of intermediate and non-classical CD80⁺ monocytes suggested a shift to a pro-inflammatory phenotype. Overall, CD163/CD80 cytofluorimetric characterization of circulating monocytes provides additional information about their polarization and could be an innovative tool to monitor aging.

Long-Term Clinical and Immunological Profile of Kidney Transplant Patients Given Mesenchymal Stromal Cell Immunotherapy

We report here the long-term clinical and immunological results of four living-donor kidney transplant patients given autologous bone marrow-derived mesenchymal stromal cells (MSCs) as part of a phase 1 study focused on the safety and feasibility of this cell therapy. According to study protocols implemented over time, based on initial early safety findings, the patients were given MSC at day 7 posttransplant (n = 2) or at day −1 pretransplant (n = 2) and received induction therapy with basiliximab and low-dose rabbit anti-thymocyte globulin (RATG) or RATG alone, and were maintained on low-dose ciclosporin (CsA)/mycophenolate mofetil (MMF). All MSC-treated patients had stable graft function during the 5- to 7-year follow-up, without increased susceptibility to infections or neoplasm. In three MSC recipients, but not historical control patients, circulating memory CD8⁺ T cell percentages remained lower than basal, coupled with persistent reduction of ex vivo donor-specific cytotoxicity. Two patients showed a long-lasting increase in the regulatory T cell/memory CD8⁺ T cell ratio, paralleled by high circulating levels of naïve and transitional B cells. In one of these two patients, CsA was successfully discontinued, and currently the low-dose MMF monotherapy is on the tapering phase. The study shows that MSC therapy is safe in the long term and could promote a pro-tolerogenic environment in selected patients. Extensive immunomonitoring of MSC-treated kidney transplant recipients could help selection of patients for safe withdrawal of maintenance immunosuppressive drugs (NCT00752479 and NCT02012153).

CD14++ CD16- monocytes are the main source of 11β-HSD type 1 after IL-4 stimulation

The anti-inflammatory actions of IL-4 are well established through earlier findings. However, the exact mechanism it uses to downregulate the pro-inflammatory cytokine production through monocytes and macrophages is poorly understood. In this study, we examined the effect of IL-4 in the induction of 11β-HSD1 in the two main classes of monocytes, CD14⁺⁺ CD16^- (CD14) and CD14⁺ CD16⁺ (CD16). Peripheral Blood Mononuclear Cells (PBMCs) were isolated from 17 healthy donors and were sorted into CD14 and CD16 subpopulations using cell sorting. Effect of IL-4 on 11β-HSD1-enzyme activity was measured in sorted and unsorted monocytes using Homogeneous Time-Resolved Fluorescence (HTRF) and M1/M2 polarization analysis was performed by flow cytometry. Our results indicate that CD14 cells are the major source of 11β-HSD1 enzyme after IL-4 stimulation and that M2 phenotype is not a pre-requisite for its synthesis.

Congenital disorder of glycosylphosphatidylinositol (GPI)-anchor biosynthesis--The phenotype of two patients with novel mutations in the PIGN and PGAP2 genes

BACKGROUND

Glycosylphosphatidylinositol (GPI)-anchor deficiencies are a new subclass of congenital disorders of glycosylation. About 26 genes are involved in the GPI-anchor biosynthesis and remodeling pathway, of which mutations in thirteen have been reported to date as causative of a diverse spectrum of intellectual disabilities. Since the clinical phenotype of these disorders varies and the number of described individuals is limited, we present new patients with inherited GPI-anchor deficiency (IGD) caused by mutations in the PGAP2 and PIGN genes.

PATIENTS AND METHODS

The first girl presented with profound psychomotor retardation, low birth parameters, and chest deformities already existing in neonatal period. The disease course was slowly progressive with severe hypotonia, chronic fever, and respiration insufficiency at the age of 6. The second girl showed profound psychomotor retardation, marked hypotonia, and high birth weight (97 centile). Dysmorphy was mild or absent in both girls. Whole exome sequencing revealed novel variants in the genes PGAP2 (c.2T>G and c.221G>A) and PIGN (c.790G>A and c.932T>G). Impaired GPI binding were was subsequently uncovered, although the hyperactivity of alkaline phosphatase (a GPI-anchored protein) occurred only in first case.

CONCLUSIONS

Based on our results we can conclude that: 1. GPI-anchor biosynthesis disorders may represent a relatively frequent and overlooked metabolic defect; 2. The utility of GPI binding assessment as a screening test for this group of rare diseases requires further studies.

Quantitative whole-cell MALDI-TOF MS fingerprints distinguishes human monocyte sub-populations activated by distinct microbial ligands

BACKGROUND

Conventionally, human monocyte sub-populations are classified according to surface marker expression into classical (CD14(++)CD16(-)), intermediate (CD14(++)CD16(+)) and non-classical (CD14(+)CD16(++)) lineages. The involvement of non-classical monocytes, also referred to as proinflammatory monocytes, in the pathophysiology of diseases including diabetes mellitus, atherosclerosis or Alzheimer's disease is well recognized. The development of novel high-throughput methods to capture functional states within the different monocyte lineages at the whole cell proteomic level will enable real time monitoring of disease states.

RESULTS

We isolated and characterized (pan-) monocytes, mostly composed of classical CD16(-) monocytes, versus autologous CD16(+) subpopulations from the blood of healthy human donors (n = 8) and compared their inflammatory properties in response to lipopolysaccharides and M.tuberculosis antigens by multiplex cytokine profiling. Following resting and in vitro antigenic stimulation, cells were recovered and subjected to whole-cell mass spectrometry analysis. This approach identified the specific presence/absence of m/z peaks and therefore potential biomarkers that can discriminate pan-monocytes from their CD16 counterparts. Furthermore, we found that semi-quantitative data analysis could capture the subtle proteome changes occurring upon microbial stimulation that differentiate resting, from lipopolysaccharides or M. tuberculosis stimulated monocytic samples.

CONCLUSIONS

Whole-cell mass spectrometry fingerprinting could efficiently distinguish monocytic sub-populations that arose from a same hematopoietic lineage. We also demonstrate for the first time that mass spectrometry signatures can monitor semi-quantitatively specific activation status in response to exogenous stimulation. As such, this approach stands as a fast and efficient method for the applied immunology field to assess the reactivity of potentially any immune cell types that may sustain health or promote related inflammatory diseases.

Monocyte subsets in schistosomiasis patients with periportal fibrosis

A major issue with Schistosoma mansoni infection is the development of periportal fibrosis, which is predominantly caused by the host immune response to egg antigens. Experimental studies have pointed to the participation of monocytes in the pathogenesis of liver fibrosis. The aim of this study was to characterize the subsets of monocytes in individuals with different degrees of periportal fibrosis secondary to schistosomiasis. Monocytes were classified into classical (CD14⁺⁺CD16⁻), intermediate (CD14⁺⁺CD16⁺), and nonclassical (CD14⁺CD16⁺⁺). The expressions of monocyte markers and cytokines were assessed using flow cytometry. The frequency of classical monocytes was higher than the other subsets. The expression of HLA-DR, IL-6, TNF-α, and TGF-β was higher in monocytes from individuals with moderate to severe fibrosis as compared to other groups. Although no differences were observed in receptors expression (IL-4R and IL-10R) between groups of patients, the expression of IL-12 was lower in monocytes from individuals with moderate to severe fibrosis, suggesting a protective role of this cytokine in the development of fibrosis. Our data support the hypothesis that the three different monocyte populations participate in the immunopathogenesis of periportal fibrosis, since they express high levels of proinflammatory and profibrotic cytokines and low levels of regulatory markers.