Deficiency In Phagocytosis Research Articles

Primary immunodeficiency disorders (PID) or inborn errors of immunity : preliminary work West Africa Côte d’Ivoire

Abstract The immune system is a particularly sophisticated protection system. As a true guardian of our health, the immune system defends our body against external or internal aggressions. Sometimes, the immune system is not able to fight because it lacks or does not function properly causing an ineffective or absent immune response. Although more than 400 diseases exist, there is no data available in our country. We analyze through a retrospective study carried out in the pediatric department at Hospital University Center, in Abidjan, between February and April 2022, involving 93 PID suspect children, the epidemiological, clinical, paraclinical and therapeutic aspects. The average age of our patients was 2 years with extremes of 22 days to 15 years, with a male predominance: sex ratio of 1.45. The predominant geographical origin was Abidjan (85.32%). Consanguinity was found in 12.9%, death in siblings was found in 3.49% of patients. The most common clinical manifestations were repeated respiratory infections (60.71%), fever (16%), severe infections at least twice a year (13.04%), persistent fungal infections (12.90), thrive retardation in 48.7%. Abnormalities such as hyperleukocytosis (42.4%), neutropenia (29.23%), lymphopenia (16.44%), thrombocytopenia (38.36%) and mostly anemia (62.36%) were noted. Phagocytosis deficiency combined immune deficiencies and humoral deficiencies were respectively found at 95.16%, 89.78%.79.03%. This work draws attention to the importance of PID which are often underdiagnosed, with absent or delayed treatment and poor prognosis. It is important to build a cohort with confirmed data to better support children with PID in our country. no support

Deficient Phagocytosis in Circulating Monocytes from Patients with COVID-19-Associated Mucormycosis.

Cases of rhino-orbital mucormycosis in patients suffering from severe coronavirus disease 2019 (COVID-19) were reported in different parts of the world, especially in India. However, specific immune mechanisms that are linked to susceptibility to COVID-19-associated mucormycosis (CAM) remain largely unexplored. We aimed to explore whether the differential regulation of circulating cytokines in CAM patients had any potential pathogenic links with myeloid phagocyte function and susceptibility to mucormycosis. A small cohort of Indian patients suffering from CAM (N = 9) as well as COVID-19 patients with no evidence of mucormycosis (N = 5) were recruited in the study. Venous blood was collected from the patients as well as from healthy volunteers (N = 8). Peripheral blood mononuclear cells and plasma were isolated. Plasma samples were used to measure a panel of 48 cytokines. CD14+ monocytes were isolated and used for a flow cytometric phagocytosis assay as well as a global transcriptome analysis via RNA-sequencing. A multiplex cytokine analysis of the plasma samples revealed reduction in a subset of cytokines in CAM patients, which is known to potentiate the activation, migration, or phagocytic activity of myeloid cells, compared to the COVID-19 patients who did not contract mucormycosis. Compared to monocytes from healthy individuals, peripheral blood CD14+ monocytes from CAM patients were significantly deficient in phagocytic function. The monocyte transcriptome also revealed that pathways related to endocytic pathways, phagosome maturation, and the cytoskeletal regulation of phagocytosis were significantly downregulated in CAM patients. Thus, the study reports a significant deficiency in the phagocytic activity of monocytes, which is a critical effector mechanism for the antifungal host defense, in patients with CAM. This result is in concordance with results regarding the specific cytokine signature and monocyte transcriptome. IMPORTANCE A number of cases of mucormycosis, often fatal, were reported among severe COVID-19 patients from India as well as from some other parts of the world. However, specific immunocellular mechanisms that underlie susceptibility to this fungal infection in COVID-19 remain largely unexplored. Our study reports a deficiency in phagocytosis by monocytes in COVID-19 patients who are concomitantly afflicted with mucormycosis, with this deficiency being linked to a characteristic monocyte transcriptome as well as a circulating cytokine signature. The functional phenotype and cytokine signature of the monocytes may provide useful biomarkers for detecting potential susceptibility to mucormycosis in COVID-19 as well as in other viral infections.

P142 Inflammatory bowel diseases associated with primary immunodeficiency: a multicenter study

Abstract Background Inflammatory bowel diseases (IBD) associated with primary immunodeficiency (PID) remain poorly known. We aimed to isolate characteristics of IBD associated with PID. Methods Using a GETAID register, we reviewed medical files of recorded patients with PID and IBD (Crohn’s disease, ulcerative colitis (UC) or microscopic colitis) followed in 9 adult university hospitals. Results of genetic investigations were available for 46 patients (62%). Results 74 patients (30 F, 44M) were included with a mean age of 26 years (median: 24 years) at diagnosis of IBD. Forty-four (59%) patients had Crohn’s disease with anoperineal lesions in 12, 26(35%) patients had microscopic (mainly lymphocytic) colitis and 4 patients had UC. PID was predominantly antibody deficiency in 40(54%) patients [34 common variable immunodeficiency, 4 X-linked agammaglobulinemia, 2 selective IgA deficiencies], disease of immune dysregulation in 18(24%) patients [CTLA4, LRBA, NFKB1, TNFAi3, XIAP deficiencies, STAT3 and STAT1 hyperactivation], phagocytosis deficiency in 15(20%) patients (12 chronic granulomatous diseases (CGD), 3 congenital neutropenia] and C1s deficiency (n=1). In order of frequency, Crohn’s disease was associated with antibody deficiencies (52%), phagocytosis deficiencies (29%) and immune dysregulation (18%), microscopic colitis with antibody deficiencies (65%), immune dysregulation (27%) and more rarely with phagocytosis deficiencies (8%) and UC with antibody deficiencies (75%) and immune dysregulation (25%). 46% of patients received immunoglobulin supplementation, 70% steroids, equally corticosteroids and budesonide, 49% biotherapy mainly anti-TNF-alpha antibody (38%) and ustekinumab (16%), 23% immunosuppressive drugs, mainly azathioprine and sirolimus and 18% aminosalicylates. Three patients (2 CGD, 1 XIAP) had been treated with allogeneic stem cell transplantation (SCT) and one patient (TNFRS13B deficiency) with autologous SCT. Eleven (15%) patients had intestinal surgery, mainly ileocecal resection. During follow-up [mean: 16 years], 51% of patients had transient or sustained clinical remission mainly with an anti-TNF-alpha antibody, ustekinumab, steroids (budesonide) and specific therapy (targeted therapy such as abatacept and ASCT), 41% of patients had severe infections, 22% developed neoplasia mainly gastrointestinal dysplasia and/or cancers (n=8), B cell lymphoma (n=3) and 4 patients died. Conclusion At adulthood in our series, IBD associated with PID are mainly Crohn’s disease and lymphocytic colitis. The first most frequent associated PID is antibody deficiency. Biotherapies (anti-TNF-alpha antibody, ustekinumab), steroids and specific therapies are commonly used to induce clinical remission.

LPS‐induced mTORC1 Signaling Activates Lipid Raft‐Actin Cytoskeletal Interactions for Phagocytosis through SREBP‐1a

There is a growing appreciation for a fundamental connection between lipid metabolism and the immune response. Macrophage phagocytosis is a signature innate immune response to pathogen exposure and cytoplasmic membrane expansion is required to engulf the phagocytic target. The sterol regulatory element binding proteins (SREBPs) are key transcriptional regulatory proteins that sense the intracellular lipid environment and modulate expression of key genes of fatty acid and cholesterol metabolism to maintain lipid homeostasis. In this study, we show that TLR4 dependent stimulation of macrophage phagocytosis requires mTORC1‐directed SREBP‐1a dependent lipid synthesis. We also show that the phagocytic defect in macrophages from SREBP‐1a deficient mice results from decreased interaction between membrane lipid rafts and the actin cytoskeleton presumably due to reduced accumulation of newly synthesized fatty acyl chains within major membrane phospholipids. We show that mTORC1 deficient macrophages also have a phagocytosis block downstream from TLR4 signaling, and interestingly, the phagocytosis deficiency in both SREBP‐1a and mTORC1 mutant macrophages can be restored by ectopic SREBP‐1a expression. Taken together, these observations indicate SREBP‐1a is a major downstream effector of TLR4‐mTORC1 directed interactions between membrane lipid rafts and the actin cytoskeleton that are required for pathogen‐stimulated phagocytosis in macrophages.Support or Funding InformationThe National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP)(2016R1A2B4008516). The National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2014R1A5A2010008).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Déficit d’activité microbicide des phagocytes mesuré par cytométrie en flux

Microbicidal activity by phagocytes is critical in protecting against bacterial or fungal infection. It is mainly due to the production or Free radical species induced by the phagocytosis. It is possible to measure directly the capacity to produce free radicles by flow cytometry (FCM) using substrates such as Dihydro-rhodamine 123 (DHR123) that become fluorescent under oxido-reduction in the presence of free radicals. This production can be triggered by bacteria or chemicals but the assay needs standardization to reach an ISO15189 accreditation level for clinical diagnosis. In this paper, we shortly describe the principle of this assay adapted from a commercial kit with some improvements. The test is directly performed on whole blood with a minimal preparation and only 20 minutes of incubation. It is calcium-dependent. As a result, CD16+ granulocytes give a straightforward response under induction by Phorbol Myristate Acetate. The response to E. coli is more heterogeneous and sometimes even stronger. Peripheral blood monocytes only give a low response. Interestingly, the response is significantly reduced in patients who had recent sever sepsis demonstrating immuno-paralysis as previously shown with other parameters. Part of this functional defect is due to a reduced opsonic activity in plasma proteins. The test appears to be robust and quite easy to be implemented in laboratory provided a minimal experience in Flow cytometry and functional tests. It is a good tool to detect primary as well as secondary deficiency in phagocytosis.

Phagocytosis Deficiency of Macrophages in NOD.H-2h4 Mice Accelerates the Severity of Iodine-Induced Autoimmune Thyroiditis.

Apoptosis occurs in many autoimmune diseases. Excess iodine induces thyrocyte apoptosis and increases the incidence and prevalence of autoimmune thyroiditis (AIT). However, the sequence of events between the appearance of thyrocyte apoptosis and the occurrence of thyroiditis remains uncharacterized. Furthermore, few studies have investigated the role of macrophage phagocytosis in the development of AIT. Therefore, we evaluated the relationship between apoptosis and inflammatory infiltration in NOD.H-2h4 mouse thyroids by comparing the sequence of events in tissue samples. We also investigated the role of macrophages by comparing macrophage phagocytosis function in BALB/c, C57BL/6, and NOD.H-2h4 mice treated with different levels of iodine. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays and thyroid inflammatory scores revealed that apoptosis (2weeks) occurred before inflammatory infiltration (4weeks). Phosphatidylserine (PS) expression on the extracellular surface of the cell membrane and double-stranded DNA fragments associated with apoptosis appeared at 2 and 8weeks, respectively. Additionally, although apoptosis was enhanced in the thyroids of mice supplemented with excess iodine (0.05±0.12 vs 1.63±0.82% for BALB/c, 0.09±0.14 vs 1.51±0.34% for C57BL/6, and 0.07±1.11 vs 4.72±0.62% for NOD.H-2h4 mice), only NOD.H-2h4 mouse thyroids presented with inflammation. Furthermore, macrophages from NOD.H-2h4 mice (44.46±1.79%) exhibited decreased phagocytotic activity relative to that in BALB/c (54.21±4.58%) and C57BL/6 (58.96±4.04%) mice. There were no differences in phagocytosis function between NOD.H-2h4 mice supplemented with excess iodine or left untreated (24.50±2.66 vs 21.71±1.79%, p=0.06). In conclusion, deficiencies in the apoptosis clearance of macrophages in NOD.H-2h4 mice may constitute an early pathogenic mechanism in AIT that is not influenced by iodine intake.

Effects of PI3Kδ-RhoA pathway on phagocytosis defect of alveolar macrophages in a mouse model of chronic obstructive pulmonary disease

Objective: To investigate effects of Phosphoinositide3-Kinases (PI3Kδ)-Ras homolog gene family member A(RhoA) pathway on phagocytosis deficiency of alveolar macrophages (AMs) in a mouse model of chronic obstructive pulmonary disease (COPD). Methods: Twenty mice were exposed to cigarette smoking to establish the COPD model, with 20 mice as the control group. AMs were isolated from lung tissue by discontinuous density gradient centrifugation and then divided into a healthy control group, a COPD group, a healthy IC87114 group and a COPD IC87114 group. The culture of IC87114 group was mixed with a final concentration of 1 nmol/L IC87114 for 24 hours. Mean fluorescence intensity (MFI) and the positive percent of AMs engulfing flurescein isothiocyanate-labeled Escherichina coli (FITC-E.coli) (AM%) were detected by flow cytometry. Real-Time PCR(RT-PCR)and Western blot were applied to detect mRNA and protein. G-LISA RhoA Kit was used to detect the activity of RhoA, and laser scanning confocal microscopy was used to observe the cytoskeleton structure of AMs. Results: Phagocytosis of AM: MFI and AM %in the COPD group [(4 512±517), (32.2±4.6)%] were decreased than those in the healthy control group [(9 857±1 042), (68.0±4.0)%, all P<0.01]. Compared with the COPD group, MFI and AM% in the COPD IC87114 group [(6 894±472), (50.6±2.1)%] were increased (all P<0.01). The expressions of mRNA and protein of PI3Kδ in the COPD group (3.14±0.54, 0.84±0.08) were increased than those in the healthy control group (1.00±0.00, 0.57±0.07) (all P<0.01). Compared with the COPD group, the expressions of mRNA and protein of PI3Kδ in the COPD IC87114 group (1.52±0.28, 0.66±0.13) were decreased (all P<0.01). The RhoA mRNA, protein and activity in the COPD group (0.70±0.07, 0.41±0.10, 0.70±0.06) were decreased compared to those in the healthy control group (1.00±0.00, 0.56±0.09, 1.19±0.09) (all P<0.01). Compared with the COPD group, the expression of mRNA, protein and activity of RhoA in the COPD IC87114 group(0.91±0.08, 0.48±0.06, 0.86±0.06) were increased (P<0.01, P<0.05). Cytoskeleton of AM: The pseudopods of the healthy control group and the healthy IC87114 group extended well, and the ability of phagocytosing FITC-E.coli was intact, but there were some defects in the COPD group. Compared with the COPD group, the COPD IC87114 group was better, both in phagocytosing and extending of pseudopods. Negative correlations existed between the mRNA, protein of PI3Kδ with mRNA, protein and activity of RhoA. Negative correlations also existed between the mRNA, protein of PI3Kδ with MFI, but positive correlations between RhoA and MFI were observed in all groups. Conclusion: The phagocytosis of AMs in COPD mice was defective, with abnormal rearrangement of the cytoskeleton. PI3Kδ negatively regulated RhoA, while PI3Kδ over activation resulted in decreasing activity of RhoA and then induced abnormal cytoskeleton rearrangement in AMs, which led to phagocytosis deficiency.IC87114 inhibited PI3Kδ activation, improved the activity of RhoA and partly recovered phagocytosis of AMs.

Effects of mTOR-Cdc42 signaling pathway on phagocytosis of alveolar macrophages in chronic obstructive pulmonary disease mice

Objective: To investigate effects of mammalian target of rapamycin (mTOR)- cell division cycle 42 (Cdc42) signaling pathway on phagocytosis of alveolar macrophages (AMs) in chronic obstructive pulmonary disease (COPD) mice. Methods: Forty mice were randomly divided into control group and model group. Each group contained 20 mice. COPD model group were established by cigarette smoking exposure. AMs were isolated from lung tissue by discontinuous density gradient centrifugation. AMs from control group were divided into health control group and rapamycin control group while AMs from model group were divided into COPD group and rapamycin COPD group. The AMs from rapamycin control group and rapamycin COPD group were incubated with a final concentration of 10 nmol/L rapamycin for 24 hours. Mean fluorescence intensity (MFI) and the positive percent of alveolar macrophage engulfed flurescein isothiocyanate-labeled Escherichina coli (FITC-E.coli) AM (AM%) were detected by flow cytometry. Real time PCR (RT-PCR) and Western blot were applied to detect mRNA and protein. The activity of Cdc42 was detected by G-LISA Small GTPase Activation Assays (G-LISA) Cdc42 Kit. The cytoskeleton structure of AM was observed by laser scanning confocal microscopy. Results: MFI and AM% in COPD group were decreased than those in health control group[4 060±590 vs 9 190±988 and (28.65±1.26)% vs (67.50±4.56)%]; Compared with COPD group, MFI and AM% in rapamycin COPD group[4 856±762, (38.31±1.71)%]were increased (all P<0.05). The expression of mRNA, protein and activity of mTOR in COPD group were increased than those in health control group[(2.62±0.46, 1.30±0.52, 1.46±0.43) vs (1.00±0.00, 0.48±0.27, 0.58±0.26)]; compared with COPD group, the expression of mRNA, protein and activity of mTOR in rapamycin COPD group (1.40±0.36, 0.90±0.66, 0.92±0.28) were decreased (all P<0.05). The Cdc42 mRNA, protein and activity in COPD group were higher than those in health control group[(2.56±0.50, 1.61±0.37, 0.46±0.09) vs (1.00±0.00, 0.67±0.22, 0.30±0.07)](all P<0.01); compared with COPD group, the expression of mRNA, protein and activity of Cdc42 in rapamycin COPD group (1.38±0.34, 0.91±0.48, 0.36±0.06) were decreased (all P<0.01). Filopodia protruding can not be seen in the cytoskeleton of AMs from health control group and rapamycin control group; some filopodia protruding can be seen in AM from COPD group; some long filopodia protruding can be seen in AM from rapamycin COPD group. Negative correlations were existed between the mRNA, protein and activity of mTOR, Cdc42 and MFI in all group. Conclusions: mTOR-Cdc42 signaling pathway is activated and related to phagocytosis deficiency of AM in COPD. It can be inferred that the pathway is involved in the pathogenesis of COPD.

CORRELATION OF THE SHEDDING OF LYMPHOCYTES RECEPTORS WITH PARAMETERS OF IMMUNOLOGIC REACTIVITY IN RESIDENTS OF THE NORTH

The study retrospectively investigated correlation characteristics of membrane and soluble forms of lymphocyte receptors in 78 healthy people living in the city of Arkhangelsk. The results of a statistical analysis allowed to evaluate the relationship of dynamic indices of shedding lymphocyte receptors CD23 and CD80 to the immunological reactivity indices. It was found that the receptors' shedding was not associated with the processes of proliferation and activation of immune cells, and the receptors abscission occurred by postmitotic mature cells. A high ratio reflecting the relationship of shedding activity of membrane forms of lymphocyte with cytokine IL-1 and IL-10 in the extracellular medium was a reflection of the biological processes regulating the in the form of feedback: increasing of receptor concentration in the extracellular medium by means of cytokine blocked cell receptor expression. Low values of the analyzed indices for CD95 receptor indicated that the cells got free from unnecessary receptor substances in the course of performing its function did not undergo apoptosis. Accumulation of receptors extracellular pool was provided by phagocytosis deficiency. Increase of phagocytosis intensity at a maximum concentration of free receptors was due to the necessity of urgent prevention of unwanted substances accumulation in the blood serum.

Neutrophil granulocyte functional status and expression of apoptosis markers in children with type 1 diabetes

In recent years, polymorphonuclear leukocytes have been proven to play an important role in the development of diabetes mellitus (DM). Neutrophil dysfunction contributes to pancreatic tissue damage as well as an increased susceptibility to infection in type 1 DM (T1DM) patients. Objective. The objective of this study was to investigate the functional activity of neutrophil granulocytes (NGs) in children with T1DM. Materials and Methods. This study involved 25 children aged 7?15 years. To evaluate programmed cell death, the number of NGs expressing apoptosis markers (CD95, CD95L and BCL2) was determined. The functional activity of NGs was determined in terms of phagocytosis and the levels of myeloperoxidase, lysosomal cationic proteins and active oxygen radicals. Results. A reduction in the bactericidal activity of NGs with deficiencies in phagocytosis, secretion of active oxygen radicals and functional reserve was found. An increase in the apoptotic potential of NGs was demonstrated, which was accompanied by an increase in CD95 expression and a decrease in BCL2 expression. An increase in the cytotoxic potential of neutrophils in the form of enhanced levels of myeloperoxidase and lysosomal cationic proteins was revealed. Conclusions. Therefore, an increase in the apoptotic potential of NGs associated with functional and metabolic changes may reflect the active involvement of NGs in the immunopathogenesis of T1DM.

Phagocytosis of neonatal pathogens by peripheral blood neutrophils and monocytes from newborn preterm and term infants

Deficiencies in phagocytosis may contribute to the increased susceptibility of infants to early life infections. Data on phagocytosis of the major neonatal pathogens Staphylococcus epidermidis (SE), Staphylococcus aureus (SA), and Escherichia coli (EC) by preterm infant leukocytes are inconsistent. Cord and <24-h peripheral blood were collected from very preterm (<30.1 wks gestational age (GA)) and term (37-42 wks GA) infants. Monocyte and neutrophil phagocytosis of pHrodo-labeled SE, SA, and EC were analyzed using a small-volume flow cytometry assay, with simultaneous characterization of surface activation marker expression. Preterm infants had lower proportions of monocytes and neutrophils capable of phagocytosis than term infants, but preterm infant phagocytes had higher phagocytic capacity. Phagocytosis was strongly correlated between cord and <24-h peripheral blood. Supplementation with exogenous complement significantly increased phagocytosis of EC but not of SE or SA. Monocyte human leukocyte antigen (HLA)-DR expression was lower in preterm infants but did not correlate with phagocytosis. There is no defect in phagocytosis by monocytes and neutrophils from preterm compared with term infants, although preterm infants possess fewer phagocytes, possibly contributing to susceptibility to bacterial infection. Further investigation into the development of postnatal phagocytic competence is warranted.

Novel role of ICAM3 and LFA-1 in the clearance of apoptotic neutrophils by human macrophages

Apoptotic cells express eat-me signals which are recognized by several receptors mainly on professional phagocytes of the mononuclear phagocyte system. This "engulfment synapse" can define a safe and effective clearance of apoptotic cells in order to maintain tissue homeostasis in the entire body. We show that the expression of four genes related to apoptotic cell clearance is strongly up-regulated in human macrophages 30min after administration of apoptotic neutrophils. Out of these the significant role of the up-regulated intercellular adhesion molecule 3 (ICAM3) in phagocytosis of apoptotic neutrophils could be demonstrated in macrophages by gene silencing as well as treatment with blocking antibodies. Blocking ICAM3 on the surface of apoptotic neutrophils also resulted in their decreased uptake which confirmed its role as an eat-me signal expressed by apoptotic cells. In macrophages but not in neutrophils silencing and blocking integrin alphaL and beta2 components of lymphocyte function-associated antigen 1 (LFA-1), which can strongly bind ICAM3, resulted in a decreased phagocytosis of apoptotic cells indicating its possible role to recognize ICAM3 on the surface of apoptotic neutrophils. Finally, we report that engulfing portals formed in macrophages during phagocytosis are characterized by accumulation of ICAM3, integrin alphaL and beta2 which show co-localization on the surface of phagocytes. Furthermore, their simultaneous knock-down in macrophages resulted in a marked deficiency in phagocytosis and a slight decrease in the anti-inflammatory effect of apoptotic neutrophils. We propose that ICAM3 and LFA-1 act as recognition receptors in the phagocytosis portals of macrophages for engulfment of apoptotic neutrophils.

Connexin43 Is Dispensable for Phagocytosis

Macrophages that lack connexin43 (Cx43), a gap junction protein, have been reported to exhibit dramatic deficiencies in phagocytosis. In this study, we revisit these findings using well-characterized macrophage populations. Cx43 knockout (Cx43(-/-)) mice die soon after birth, making the harvest of macrophages from adult Cx43(-/-) mice problematic. To overcome this obstacle, we used several strategies: mice heterozygous for the deletion of Cx43 were crossed to produce Cx43(+/+) (wild type [WT]) and Cx43(-/-) fetuses. Cells isolated from 12- to 14-d fetal livers were used to reconstitute irradiated recipient animals. After reconstitution, thioglycollate-elicited macrophages were collected by peritoneal lavage and bone marrow was harvested. Bone marrow cells and, alternatively, fetal liver cells were cultured in media containing M-CSF for 7-10 d, resulting in populations of cells that were >95% macrophages based on flow cytometry. Phagocytic uptake was detected using flow cytometric and microscopic techniques. Quantification of phagocytic uptake of IgG-opsonized sheep erythrocytes, zymosan particles, and Listeria monocytogenes failed to show any significant difference between WT and Cx43(-/-) macrophages. Furthermore, the use of particles labeled with pH-sensitive dyes showed equivalent acidification of phagosomes in both WT and Cx43(-/-) macrophages. Our findings suggest that modulation of Cx43 levels in cultured macrophages does not have a significant impact on phagocytosis.

Regulation of TREM2 expression by an NF-кB-sensitive miRNA-34a

Genetic deficits and loss of function for the triggering receptor expressed in myeloid cells 2 (TREM2; encoded at chr6p21.1), a transmembrane spanning stimulatory receptor of the immunoglobulin/lectin-like gene superfamily, have been associated with deficiencies in phagocytosis and the innate immune system in Alzheimer's disease. In this study, we provide evidence that TREM2 is downregulated in samples of sporadic Alzheimer hippocampal CA1 compared with age-matched controls. A nuclear factor-кB (NF-кB)-sensitive miRNA-34a (encoded at chr1p36.22), upregulated in Alzheimer's disease, was found to target the 299 nucleotide human TREM2 mRNA 3'-untranslated region (3'-UTR) and downregulate the expression of a TREM2-3'-UTR reporter vector. A stabilized anti-miRNA-34a (AM-34a) quenched this pathogenic response. The results suggest that an epigenetic mechanism involving an NF-кB-mediated, miRNA-34a-regulated downregulation of TREM2 expression may shape innate immune and phagocytic responses that contribute to inflammatory neurodegeneration.

Autoimmune Kidney Disease and Impaired Engulfment of Apoptotic Cells in Mice with Macrophage Peroxisome Proliferator-Activated Receptor γ or Retinoid X Receptor α Deficiency

Autoimmune glomerulonephritis is a common manifestation of systemic lupus erythematosus (SLE). In this study, we show that mice lacking macrophage expression of the heterodimeric nuclear receptors PPARγ or RXRα develop glomerulonephritis and autoantibodies to nuclear Ags, resembling the nephritis seen in SLE. These mice show deficiencies in phagocytosis and clearance of apoptotic cells, and they are unable to acquire an anti-inflammatory phenotype upon feeding of apoptotic cells, which is critical for the maintenance of self-tolerance. These results demonstrate that stimulation of PPARγ and RXRα in macrophages facilitates apoptotic cell engulfment, and they provide a potential strategy to avoid autoimmunity against dying cells and to attenuate SLE.

Yersinia pestis and host macrophages: immunodeficiency of mouse macrophages induced by YscW

The virulence of the pathogenic Yersinia species depends on a plasmid-encoded type III secretion system (T3SS) that transfers six Yersinia outer protein (Yop) effector proteins into the cytoplasm of eukaryotic cells, leading to disruption of host defence mechanisms. It is shown in this study that Yersinia pestis YscW, a protein of the T3SS injectisome, contributes to the induction of a deficiency in phagocytosis in host macrophages and a reduction in their antigen-presenting capacity. A Y. pestis strain lacking yscW had no effect on uptake by host macrophages. In mice infected with wild-type Y. pestis, the yscW mutant or a complement strain, immunodeficiency was observed in host macrophages compared with those from uninfected mice. However, the phagocytosis and antigen presenting capacities of macrophages infected by yscW mutant strain both in vivo and in vitro were significantly higher than those by wild type strain. Consistent with this finding, when YscW was expressed in the RAW264.7 macrophage cell line, phagocytosis and antigen-presenting capacities were significantly lower than those of the control groups. These results indicate that Y. pestis YscW may directly induce immunodeficiency in murine macrophages by crippling their phagocytosis and antigen-presenting capacities. These data provide evidences to Y. pestis pathogenesis that some proteins in T3SS injectisome, such as YscW protein, might play independent roles in disrupting host defense apart from their known functions.

Gas6 and the Tyro 3 receptor tyrosine kinase subfamily regulate the phagocytic function of Sertoli cells

The apoptotic spermatogenic cells and residual bodies are phagocytosed and degraded by Sertoli cells during spermatogenesis. The mechanisms of this process are largely unknown. Here, we demonstrate that Gas6 and its receptors, the Tyro 3 subfamily of receptor tyrosine kinases (RTKs; Tyro 3, Axl, and Mer), regulate the phagocytic function of Sertoli cells. The phagocytic ability of Sertoli cells increased by five times in the presence of Gas6 in serum-free medium when compared with controls. The Sertoli cells lacking Mer showed a 35% reduction in phagocytosis of apoptotic spermatogenic cells when compared with wild-type (WT) controls, whereas the Sertoli cells lacking Tyro 3 or Axl exhibited phagocytic activity comparable with the controls. Notably, the Sertoli cells lacking all three members of the Tyro 3 RTK subfamily showed a dramatic decrease in phagocytic ability of 7.6-fold when compared with WT Sertoli cells. The deficiency in phagocytosis by the triple-mutant Sertoli cells was due to the deficit in binding of the Sertoli cells to apoptotic germ cells. These findings suggest that Mer is responsible for triggering phagocytosis of apoptotic spermatogenic cells by Sertoli cells and that Tyro 3, Axl, and Mer participate in recognizing and binding apoptotic germ cells by Sertoli cells in a redundant manner. Gas6 is a functional ligand of the Tyro 3 RTK subfamily in mediating phagocytic ability of Sertoli cells.

Phagocytosis of apoptotic cells by macrophages from NOD mice is reduced.

Macrophages limit inflammatory responses by clearing apoptotic cells. Deficiencies in apoptotic cell phagocytosis have been linked to autoimmunity. In this study, we determined the efficiency with which macrophages from diabetes-prone NOD and diabetes-resistant NOR, Idd5, Balb/c, and C57BL/6 mice phagocytose apoptotic thymocytes and NIT-1 insulinoma cells. Peritoneal and bone marrow-derived macrophages from NOD mice engulfed fewer apoptotic thymocytes than macrophages from Balb/c mice (P < 0.05). Peritoneal macrophages from NOR and Idd5 NOD congenic mice were more proficient at engulfment than their NOD counterparts. Annexin V blockade diminished apoptotic thymocyte clearance and heat-labile serum factors augmented clearance. Binding of apoptotic thymocytes to NOD macrophages was also reduced, suggesting that the deficiency in phagocytosis may be partly attributable to a recognition defect. Peritoneal macrophages from female Balb/c and NOD mice were equally efficient in the engulfment of microspheres, suggesting that the phagocytic deficiency observed in NOD mice was specific for apoptotic cells. In summary, we have demonstrated a deficiency in phagocytic function of macrophages from NOD mice. Normal and diabetes-prone neonatal rodents have a wave of beta-cell apoptosis coincident with the onset of target organ inflammation. A constitutive defect in the clearance of apoptotic beta-cells may be contributory to the initiation of autoimmunity.

BCG-LYMPHADENITIS IN CHILDREN WITH CHRONIC GRANULOMATOUS DISEASE. 74

For the period 1994-1996, five boys with x-linked recessive form of chronic granulomatosis disease (CGD) were diagnosed and treated in Children's Oncohematology Clinic in Sofia, Bulgaria. The patients were hospitalized for anemia and marked hepatosplenomegaly. All 5 patients had BCG-lymphadenitis and some of them had fistulisation of the lymph nodes. The history of relapsing skin and lung infections, otitis and torpid evolution of a specific lymphadenitis raised the clinical suspicion of CGD. Primary immune deficiency in phagocytosis was documented with a positive NBT-test in all 5 patients, their mothers and some of their relatives.

Deficiencies in collagen phagocytosis by human fibroblasts in vitro: a mechanism for fibrosis?

Degradation of collagen by fibroblast phagocytosis is an important pathway for physiological remodelling of soft connective tissues. Perturbations of this pathway may provide a mechanism for the development of fibrotic lesions. As collagen phagocytosis may be regulated by either a change of the proportions or the activity of phagocytic cells, we quantified phagocytosis with an in vitro model system. Collagen-coated fluorescent latex beads were incubated with human gingival fibroblasts and the fluorescence associated with internalized beads was measured by flow cytometry. Cells from normal tissues that had been incubated with beads for 3 hours contained a mean of 64% phagocytic cells; however, a small subpopulation (10% of phagocytic cells) contained more than threefold higher numbers of beads per cell than the mean. In contrast, cells from fibrotic lesions exhibited a large reduction of the proportions of phagocytic cells (mean = 13.8%) and there were no cells with high numbers of beads. On the basis of 3H-Tdr labeling, cells from fibrotic lesions that had internalized beads failed to proliferate, in contrast to phagocytic cells from normal tissues, which underwent repeated cell divisions. This result was not due to variations of cell cycle phase as there was no preferential internalization of beads during different phases of the cell cycle. The low phagocytic rate of cells from fibrotic lesions was also not due to asymmetric partitioning of phagosomes at mitosis as videocinemicrography of bead-labeled phagosomes in single, pre-mitotic cells demonstrated that > 90% of phagocytic cells equally partitioned beads to daughter cells. To investigate if inhibition of phagocytosis could be replicated in vitro, cells were incubated with the fibrosis-inducing drugs nifedipine or dilantin. These cultures exhibited marked (15-75%), dose-dependent reductions in the proportions of phagocytic cells, but there was no reduction in bead number per cell. Fibrotic lesions appear to contain fibroblasts with marked deficiencies in phagocytosis and the reduced phagocytic activity of these cells may contribute to unbalanced degradation and fibrosis.