Role of FcgammaRI (CD64) in erythrocyte elimination and its up-regulation in thalassaemia

The effects of Phorbol 12-myristate 13-acetate concentration on the expression of miR-155 and miR-125b and their macrophage function-related genes in the U937 cell line

The phorbol 12-myristate 13-acetate (PMA)-induced U937 cell line has been widely used as an in vitro model for studying the functions of human macrophages. However, there are several concentrations of PMA commonly used to drive the differentiation of monocytic cell line to macrophage. Also, the expression of microRNA-155 (miR-155) and miR-125b in PMA-treated human monocytic cell line has not yet been reported. The five usual concentrations of PMA for stimulating macrophage differentiation are 10, 25, 50, 100, and 200 nM. In this study we compared the expression levels of miR-155, miR-125b and their related genes involved in macrophage functions in U937-derived cells after treatment with those five concentrations. The morphological study results showed that the five concentrations of PMA could induce macrophage differentiation in a similar manner. Moreover, cell proliferation and viability were not significantly different among these five conditions excepted the lower cell viability at 200 nM of PMA treatment. The five concentrations of PMA could upregulate the expression of miR-155 and miR-125b and increase the phagocytic activity of U937-derived cells in dose-reversal manner. The upregulation of miR-155 was correlated with increased expression levels of TNFα and decreased expression levels of BACH1 and CEBPβ, while the reduction of IRF4 was correlated with increased expression levels of miR-125b. Our study found that PMA could stimulate macrophage differentiation in a broad range of concentrations, however, the lower concentration could upregulate the higher expression of both miR-155 and miR-125b, and that correlated with the phagocytic functional activity of U937-derived macrophages.

Anemia Severity in β-Thalassemia Correlates with Elevated Levels of microRNA-125b in Activated Phagocytic Monocytes

β-Thalassemia (β-thal), is an inherited blood disorder caused by reduced or absent synthesis of β-globin chains leading to imbalance of globin chain synthesis. The clearance of β-thalassemic abnormal red blood cells (RBCs) that result from excessive unbound α-globin is mainly achieved by activated monocytes. The phagocytic activity of β-thal monocytes significantly increases when co-cultured with normal and β-thal RBC individuals compare to that of normal monocytes co-cultured with normal RBCs. The present study indicates that microRNA (miR) plays a role in monocyte activation. In this study, we identified the higher miR-125b expression in CD14 marker-positive monocytic cells of β-thal patients. Moreover, miR-125b expression levels positively correlate with the phagocytic activity of monocytes. Remarkably, miR-125b expression levels are negatively correlated with RBC count, hemoglobin (Hb) and hematocrit [or packed cell volume (PCV)], which are the indices for the severity of anemia. From these findings, our future studies will be to prove the hypothesis that miR-125b expression in activated monocytes may be a genetic modifier related to the severity of anemia in β-thal patients.

Intracellular iron overload leading to DNA damage of lymphocytes and immune dysfunction in thalassemia major patients

OBJECTIVES

To investigate the cause and effects of intracellular iron overload in lymphocytes of thalassemia major patients.

METHODS

Sixty-six thalassemia major patients having iron overload and 10 age-matched controls were chosen for the study. Blood sample was collected, and serum ferritin, oxidative stress; lymphocyte DNA damage were examined, and infective episodes were also counted.

RESULTS

Case-control analysis revealed significant oxidative stress, iron overload, DNA damage, and rate of infections in thalassemia cases as compared to controls. For cases, oxidative stress (ROS) and iron overload (serum ferritin) showed good correlation with R²  = 0.934 and correlation between DNA damage and ROS gave R²  = 0.961. We also demonstrated that intracellular iron overload in thalassemia caused oxidative damage of lymphocyte DNA as exhibited by DNA damage assay. The inference is further confirmed by partial inhibition of such damage by chelation of iron and the concurrent lowering of the ROS level in the presence of chelator deferasirox.

CONCLUSION

Therefore, intracellular iron overload caused DNA fragmentation, which may ultimately hamper lymphocyte function, and this may contribute to immune dysfunction and increased susceptibility to infections in thalassemia patients as indicated by the good correlation (R²  = 0.91) between lymphocyte DNA damage and rate of infection found in this study.

MiR-155 enhances phagocytic activity of β-thalassemia/HbE monocytes via targeting of BACH1

Abnormal red blood cell (RBC) clearance in β-thalassemia is triggered by activated monocytes. Recent reports indicate that miRNA (miR-) plays a role in monocyte activation. To study phagocytic function, we co-cultured monocytes of normal, non-splenectomized and splenectomized β-thalassemia/HbE individuals with RBCs obtained from normal, non-splenectomized and splenectomized β-thalassemia/HbE individuals. The phagocytic activity of β-thalassemia/HbE monocytes co-cultured with β-thalassemia/HbE RBCs was significantly higher than that of normal monocytes co-cultured with normal RBCs. Upregulation of monocyte miR-155 was observed in β-thalassemia/HbE patients. Increased miR-155 was associated with reductions in BTB and CNC Homology1 (BACH1) target gene expression and increased phagocytic activity of β-thalassemia/HbE monocytes. Taken together, these findings suggested that increased miR-155 expression in activated monocytes leads to enhanced phagocytic activity via BACH-1 regulation in β-thalassemia/HbE. This provides novel insights into the phagocytic clearance of abnormal RBCs in β-thalassemia/HbE.

FcγRI (CD64): an identity card for intestinal macrophages

Macrophages are becoming increasingly recognized as key cellular players in intestinal immune homeostasis. However, differentiating between macrophages and dendritic cells (DCs) is often difficult, and finding a specific phenotypic signature for intestinal macrophage identification has remained elusive. In this issue of the European Journal of Immunology, Tamoutounour et al. [Eur. J. Immunol. 2012. 42: 3150-3166] identify CD64 as a specific macrophage marker that can be used to discriminate DCs from macrophages in the murine small and large intestine, under both steady-state and inflammatory conditions. The authors also propose a sequential 'monocyte-waterfall' model for intestinal macrophage differentiation, with implications for immune tolerance and inflammation at the gut mucosal interface. This Commentary will discuss the advantages and potential limitations of CD64 as a marker for intestinal macrophages.

Infections in thalassemia and hemoglobinopathies: focus on therapy-related complications

The clinical approach to thalassemia and hemoglobinopathies, specifically Sickle Cell Disease (SCD), based on transfusions, iron chelation and bone marrow transplantation has ameliorated their prognosis. Nevertheless, infections still may cause serious complications in these patients. The susceptibility to infections in thalassemia and SCD arises both from a large spectrum of immunological abnormalities and from exposure to specific infectious agents. Four fundamental issues will be focused upon as central causes of immune dysfunction: the diseases themselves; iron overload, transfusion therapy and the role of the spleen. Thalassemia and SCD differ in their pathogenesis and clinical course. It will be outlined how these differences affect immune dysfunction, the risk of infections and the types of most frequent infections in each disease. Moreover, since transfusions are a fundamental tool for treating these patients, their safety is paramount in reducing the risks of infections. In recent years, careful surveillance worldwide and improvements in laboratory tests reduced greatly transfusion transmitted infections, but the problem is not completely resolved. Finally, selected topics will be discussed regarding Parvovirus B19 and transfusion transmitted infections as well as the prevention of infectious risk postsplenectomy or in presence of functional asplenia.

Impaired phagocyte antibacterial effector functions in beta-thalassemia: a likely factor in the increased susceptibility to bacterial infections

Bacterial diseases are serious complications of beta-thalassemia syndromes but the mechanisms underlying the increased susceptibility to these infections are not fully understood. Factors which are likely to be involved are anemia, splenectomy, iron-overload and alterations in innate/adaptive immune responses. There is substantial evidence that a defect in innate effector functions of phagocytes (neutrophils, monocytes/macrophages) plays an important role in the weakened resistance to pathogenic bacteria and is at least in part due to iron overload. There is substantial evidence of an iron-related defect in bacterial phagocytosis by neutrophils. Moreover, reduced chemotaxis by these phagocytes has been repeatedly demonstrated. Similarly, an impairment of monocyte bacterial phagocytosis and generation of anti-bacterial compounds have recently been delineated but any relation to iron overload needs to be established. Additional mechanisms of defective innate immune responses such as altered expression of pathogen recognising receptors and function seem possible and have to be explored. Further insight into innate phagocyte effector functions in beta-thalassemia is essential for understanding the increased susceptibility to bacterial infections and their management.

The importance of erythroid expansion in determining the extent of apoptosis in erythroid precursors in patients with β-thalassemia major

Beta-thalassemia major is characterized by ineffective erythropoiesis leading to severe anemia and extensive erythroid expansion. The ineffective erythropoiesis is in part due to accelerated apoptosis of the thalassemic erythroid precursors; however, the extent of apoptosis is surprisingly variable. To understand this variability as well as the fact that some patients undergoing allogeneic marrow transplantation are resistant to the myeloablative program, we attempted more quantitative analyses. Two groups of patients totaling 44 were studied, along with 25 healthy controls, and 7 patients with hemolysis and/or ineffective erythropoeisis. By 2 flow cytometric methods, thalassemic erythroid precursors underwent apoptosis at a rate that was 3 to 4 times normal. Because thalassemic marrow has between 5- to 6-fold more erythroid precursors than healthy marrow, this translated into an absolute increase in erythroid precursor apoptosis of about 15-fold above our healthy controls. In searching for the causes of the variability in thalassemic erythroid precursor apoptosis, we discovered tight direct correlations between the relative and absolute extent of apoptosis and the extent of erythroid expansion as measured either by the absolute number of marrow erythroid precursors or by serum soluble transferrin receptor levels. These results could mean that the most extreme rates of erythroid proliferation lend themselves to cellular errors that turn on apoptotic programs. Alternatively, extreme rates of erythroid hyperplasia and apoptosis might be characteristic of more severely affected patients. Lastly, extreme erythroid hyperplasia could generate such numbers of apoptotic erythroid precursors that marrow macrophages are overwhelmed, leaving more apoptotic cells in the sample.

The importance of erythroid expansion in determining the extent of apoptosis in erythroid precursors in patients with β-thalassemia major

Beta-thalassemia major is characterized by ineffective erythropoiesis leading to severe anemia and extensive erythroid expansion. The ineffective erythropoiesis is in part due to accelerated apoptosis of the thalassemic erythroid precursors; however, the extent of apoptosis is surprisingly variable. To understand this variability as well as the fact that some patients undergoing allogeneic marrow transplantation are resistant to the myeloablative program, we attempted more quantitative analyses. Two groups of patients totaling 44 were studied, along with 25 healthy controls, and 7 patients with hemolysis and/or ineffective erythropoeisis. By 2 flow cytometric methods, thalassemic erythroid precursors underwent apoptosis at a rate that was 3 to 4 times normal. Because thalassemic marrow has between 5- to 6-fold more erythroid precursors than healthy marrow, this translated into an absolute increase in erythroid precursor apoptosis of about 15-fold above our healthy controls. In searching for the causes of the variability in thalassemic erythroid precursor apoptosis, we discovered tight direct correlations between the relative and absolute extent of apoptosis and the extent of erythroid expansion as measured either by the absolute number of marrow erythroid precursors or by serum soluble transferrin receptor levels. These results could mean that the most extreme rates of erythroid proliferation lend themselves to cellular errors that turn on apoptotic programs. Alternatively, extreme rates of erythroid hyperplasia and apoptosis might be characteristic of more severely affected patients. Lastly, extreme erythroid hyperplasia could generate such numbers of apoptotic erythroid precursors that marrow macrophages are overwhelmed, leaving more apoptotic cells in the sample.