Absence of platelet CD40L identifies patients with X-linked hyper IgM syndrome

The hyper IgM syndromes: Epidemiology, pathogenesis, clinical manifestations, diagnosis and management

Hyper Immunoglobulin M syndrome (HIGM) is a rare primary immunodeficiency disorder characterized by low or absent levels of serum IgG, IgA, IgE and normal or increased levels of serum IgM. Various X-linked and autosomal recessive/dominant mutations have been reported as the underlying cause of the disease. Based on the underlying genetic defect, the affected patients present a variety of clinical manifestations including pulmonary and gastrointestinal complications, autoimmune disorders, hematologic abnormalities, lymphoproliferation and malignancies which could be controlled by multiple relevant therapeutic approaches. Herein, the epidemiology, pathogenesis, clinical manifestations, diagnosis, management, prognosis and treatment in patients with HIGM syndrome have been reviewed.

Specific binding of hypochlorite-oxidized HDL to platelet CD36 triggers proinflammatory and procoagulant effects

OBJECTIVE

Oxidative stress and systemic inflammation negatively affect several protective functions of high density lipoproteins (HDL) and oxidative modification of HDL by the inflammation-derived oxidant hypochlorite converts HDL into a potent platelet agonist. Therefore it was the aim of this work to clarify if these platelet-activating effects result from specific binding of hypochlorite-oxidized HDL (hyp-OxHDL) to the platelet surface and to identify responsible receptors.

METHODS

Binding and functional studies were performed with hyp-OxHDL in absence and presence of (potential) competitors in normal and CD36-deficient human platelets. Platelet aggregation was quantified by light transmission aggregometry. Surface expression of CD62P, phosphatidylserine and CD40L was quantified by flow cytometry.

RESULTS

Binding studies reveal that hyp-OxHDL show specific and saturable high-affinity binding to the platelet surface. Hyp-OxHDL trigger platelet aggregation and in a dose dependent way provoke the release of significant amounts of CD40L as well as phosphatidylserine on the platelet surface. Blocking specific binding of hyp-OxHDL to the platelet surface interferes with the ability of hyp-OxHDL to stimulate human platelets. CD36-deficient human platelets show markedly reduced binding of hyp-OxHDL. Upon addition of hypochlorite-oxidized HDL, CD36-deficient platelets do not aggregate and completely fail to release CD40L or phosphatidylserine.

CONCLUSIONS

From these results we conclude that specific binding of hyp-OxHDL to platelet CD36 is essential for the proinflammatory and procoagulant effects of hyp-OxHDL shown within this work. The contribution of other receptors besides CD36 to specific binding of hyp-OxHDL to the platelet membrane appears to be minimal, at best.

Age-related Epstein-Barr virus (EBV)-associated B-cell lymphoproliferative disorders: comparison with EBV-positive classic Hodgkin lymphoma in elderly patients

Age-related Epstein-Barr virus-associated B-cell lymphoproliferative disorder (aEBVLPD) is a disease group characterized by EBV-associated large B-cell lymphoma in elderly without predisposing immunodeficiency. In nearly one- third of cases, aEBVLPD occurs as a polymorphous subtype with reactive cell-rich components, bearing a morphologic similarity to classic Hodgkin lymphoma (cHL). The aim of this study was to clarify clinicopathologic differences between the polymorphic subtype of aEBVLPD (n = 34) and EBV(+) cHL (n = 108) in patients aged 50 years or older. Results showed that aEBVLPD was more closely associated with aggressive clinical parameters than cHL, with a higher age at onset (71 vs 63 years); lower male predominance (male-female ratio, 1.4 vs 3.3); and a higher rate of involvement of the skin (18% vs 2%), gastrointestinal tract (15% vs 4%), and lung (12% vs 2%). aEBVLPD was histopathologically characterized by a higher ratio of geographic necrosis, greater increase (> 30%) in cytotoxic T cells among background lymphocytes, higher positivity for CD20 and EBNA2, and absence of CD15 expression. As predicted by the clinical profile, aEBVLPD had a significantly poorer prognosis than EBV(+) cHL (P < .001). The polymorphous subtype of aEBVLPD constitutes an aggressive group with an immune response distinct from EBV(+) cHL, and requires the development of innovative therapeutic strategies.

Nuclear factor of activated T cells (NFAT) mediates CD154 expression in megakaryocytes

Platelets are an abundant source of CD40 ligand (CD154), an immunomodulatory and proinflammatory molecule implicated in the onset and progression of several inflammatory diseases, including systemic lupus erythematosus (SLE), diabetes, and cardiovascular disease. Heretofore considered largely restricted to activated T cells, we initiated studies to investigate the source and regulation of platelet-associated CD154. We found that CD154 is abundantly expressed in platelet precursor cells, megakaryocytes. We show that CD154 is expressed in primary human CD34+ and murine hematopoietic precursor cells only after cytokine-driven megakaryocyte differentiation. Furthermore, using several established megakaryocyte-like cells lines, we performed promoter analysis of the CD154 gene and found that NFAT, a calcium-dependent transcriptional regulator associated with activated T cells, mediated both differentiation-dependent and inducible megakaryocyte-specific CD154 expression. Overall, these data represent the first investigation of the regulation of a novel source of CD154 and suggests that platelet-associated CD154 can be biochemically modulated.

Platelet and soluble CD40L in meningococcal sepsis

OBJECTIVE

To determine the influence of meningococcal sepsis on levels of platelet derived CD40L and on endothelial CD40 expression.

DESIGN AND SETTING

Prospective observational study in two tertiary paediatric intensive care units.

PATIENTS AND PARTICIPANTS

63 children with meningococcal sepsis and 10 age-matched controls.

MEASUREMENTS AND RESULTS

(a) sCD40L ELISA of plasma from patients with meningococcal sepsis (n = 49) and age matched controls (n = 10). This demonstrated higher sCD40L levels in patients (median 0.29 ng/ml, IQR 0.2-0.41) than controls (0.09 ng/ml, 0.08-0.12). However, there was no relationship between plasma sCD40L level and platelet count or disease severity. (b) Flow cytometry of fresh blood from patients with meningococcal sepsis (n = 11) and age-matched controls (n = 10) for membrane bound CD40L and CD62P on circulating platelets. This demonstrated low levels of CD40L and CD62P in patients and controls. CD40L+ platelets were 3.5% (3.0-4.8) in patients and 4.9% (3.5-4.3) in controls. CD62P+ platelets were 10.7% (6.4-12.8) in patients and 7.9% (5.9-13.0) in controls. (c) Immunohistochemistry of skin biopsy specimens from six patients, staining for endothelial CD40 expression at sites of microthrombus formation, which demonstrated preserved CD40 expression in vascular endothelium at sites of microthrombus formation.

CONCLUSIONS

The elevated sCD40L level in meningococcal sepsis implies release of sCD40L from platelets. However, there was no relationship between plasma sCD40L level and the degree of thrombocytopenia or disease severity. Furthermore, platelet surface bound CD40L was similar in controls and patients. Thus, further investigation is needed to determine whether platelet CD40L contributes to inflammation and thrombosis in MCS.

Analysis of serum soluble CD40 ligand (sCD40L) in the patients undergoing allogeneic stem cell transplantation: platelet is a major source of serum sCD40L

CD40 ligand (CD40L) is expressed not only on activated T cells but also on activated platelets. A soluble CD40 ligand (sCD40L) is released from the activated T cells and platelets by ill-defined proteolytic process in vitro. It has been reported that sCD40L is elevated in the serum of patients with systemic lupus erythematosus, unstable angina, essential thrombocythemia, and autoimmune thrombocytopenic purupura. However, source of sCD40L in vivo remains to be elucidated. We investigated the serial sCD40L in the serum in patients undergoing allogeneic stem cell transplantation and compared with the platelets number and soluble IL2R, which is a marker of activated T cells. The value of sCD40L was well correlated with platelet number or thrombopoiesis. In cases of severe graft vs. host disease with markedly increased sIL2R, sCD40L was not increased in vivo. These results indicate that sCD40L in vivo is released mainly from the platelets or in the process of platelet production but not from the activated T cells.

Current applications of flow cytometry in the diagnosis of primary immunodeficiency diseases

CONTEXT

To review the applications of flow cytometry in the diagnosis and management of primary immunodeficiency disease.

DATA SOURCES

Articles describing the use of flow cytometry in the diagnosis of several primary immunodeficiency diseases were obtained through the National Library of Medicine database.

STUDY SELECTION

Publications that described novel and known applications of flow cytometry in primary immunodeficiency disease were selected. Review articles were included. Articles describing the different immunodeficiency diseases and methods of diagnosis were also selected.

DATA EXTRACTION

Approximately 100 data sources were analyzed, and those with the most relevant information were selected.

DATA SYNTHESIS

The diagnosis of many primary immunodeficiency diseases requires the use of several laboratory tests. Flow cytometry has become an important part of the workup of individuals suspected to have such a disorder. Knowledge of the pathogenesis of many of these diseases continues to increase, hence we acquire a better understanding of the laboratory tests that may be helpful in diagnosis.

CONCLUSIONS

Flow cytometry is applicable in the initial workup and subsequent management of several primary immunodeficiency diseases. As our understanding of the pathogenesis and management of these diseases increases, the use of many of these assays may become routine in hospitals.

CD40 is constitutively expressed on platelets and provides a novel mechanism for platelet activation

CD40 is a 48-kDa phosphorylated transmembrane glycoprotein belonging to the TNF receptor superfamily. CD40 has been demonstrated on a range of cell types, and it has an important role in adaptive immunity and inflammation. CD40 has recently been described on platelets but platelet activation by CD40 has not been described. In the present study, we use flow cytometry and immunoblotting to confirm that platelets constitutively express surface CD40. CD40 mRNA was undetectable, suggesting that the protein is synthesized early in platelet differentiation by megakaryocytes. Ligation of platelet CD40 with recombinant soluble CD40L trimer (sCD40LT) caused increased platelet CD62P expression, alpha-granule and dense granule release, and the classical morphological changes associated with platelet activation. CD40 ligation also caused beta3 integrin activation, although this was not accompanied by platelet aggregation. These actions were abrogated by the CD40L blocking antibody TRAP-1 and the CD40 blocking antibodies M2 and M3, showing that activation was mediated by CD40L binding to platelet CD40. beta3 integrin blockade with eptifibatide had no effect, indicating that outside-in signaling via alphaIIbbeta3 was not contributing to these CD40-mediated effects. CD40 ligation led to enhanced platelet-leukocyte adhesion, which is important in the recruitment of leukocytes to sites of thrombosis or inflammation. Our results support a role for CD40-mediated platelet activation in thrombosis, inflammation, and atherosclerosis.

Senile EBV+ B-cell lymphoproliferative disorders: a clinicopathologic study of 22 patients

Twenty-two Epstein-Barr virus-associated B-cell lymphoproliferative disorders (LPDs) without predisposing immunodeficiencies were evaluated clinically and pathologically. All patients were Japanese and negative for anti-human immunodeficiency virus antibody. They were all more than 60 years old with a median age of 75.5 years. Eighteen (82%) patients showed extranodal involvement. Biopsied specimens contained variable numbers of centroblasts, immunoblasts, and Reed-Sternberg-like giant cells often with necrosis and an angiocentric pattern. The 13 cases showing polymorphous composition and inflammatory background were categorized as polymorphic LPD subtype. The other nine cases contained diffuse proliferative lesions of large lymphoid cells and were categorized as large cell lymphoma subtype. Tumor cells expressed CD20 and/or CD79a, and in situ hybridization showed them to be associated with Epstein-Barr virus. LMP1 was detected in all cases and EBNA2 in seven. Eighteen patients initially received combination chemotherapy, and 12 achieved complete remission. However, six patients were refractory to chemotherapy and four patients with complete remission later relapsed. Eight of the 18 patients who received chemotherapy showed an aggressive disease course within a year after the diagnosis. There was a significant difference in prognosis between the group with polymorphic LPDs and the one with large cell lymphomas (p = 0.003). Although the disease profile of the 22 cases was analogous to that of immunodeficiency-associated B-cell LPDs, none of the patients showed evidence of underlying immunodeficiency-related diseases. These findings suggest that Epstein-Barr virus-associated LPD without immunodeficiency mainly occurs in elderly patients. Further investigations are needed to clarify the pathogenesis of this disease and to determine the optimal treatment strategy.

The hyper IgM syndrome

The hyper IgM syndrome is a rare, inherited immune deficiency disorder resulting from defects in the CD40 ligand/CD40-signaling pathway. X-linked hyper IgM is caused by defects in the CD40 ligand gene, while autosomal recessive hyper IgM is caused by defects in the CD40-activated RNA-editing enzyme, activation-induced cytidine deaminase, which is required for immunoglobulin isotype switching and somatic hypermutation in B cells. The loss of interaction between CD40 and its ligand in X-linked hyper IgM results in an impairment of T cell function, of B cell differentiation, and of monocyte function, while only B cell differentiation appears to be affected in autosomal recessive hyper IgM. With genetic defects in the hyper IgM syndrome identified, it is possible to diagnose patients definitely, to perform genetic screening, and to delineate the clinical manifestations of this syndrome. Further research may lead to novel and definitive therapeutic options for patients with hyper IgM syndrome.

Platelet and leucocyte activation in childhood sickle cell disease: association with nocturnal hypoxaemia

We hypothesized that vaso-occlusive events in childhood sickle cell disease (SCD) may relate to inflammatory cell activation as well as interactions between sickle erythrocytes and vascular endothelium. Peripheral blood was examined from 24 children with SCD, of whom 12 had neurological sequelae and seven had frequent painful crises, and 10 control subjects. Platelet (CD62P and CD40L expression) and granulocyte (CD11b expression) activation and levels of platelet-erythrocyte and platelet-granulocyte complexes were determined by flow cytometry. Platelets (P = 0.019), neutrophils (P = 0.02) and monocytes (P = 0.001) were more activated and there were increased platelet-erythrocyte complexes (P = 0.026) in SCD patients compared with controls. Platelet-granulocyte complexes were not raised. There were no differences between the different groups of SCD. As hypoxia activates monocytes, platelets and endothelial cells and causes sickling of SCD erythrocytes, we also investigated 20 SCD patients with overnight pulse oximetry. Minimum overnight saturation correlated with the level of platelet-erythrocyte complexes (Spearman's rho -0.668, P < 0.02), neutrophil CD11b (Spearman's rho -0.466, P = 0.038) and monocyte CD11b (Spearman's rho -0.652, P = 0. 002). These findings provide important clues about the mechanism by which SCD patients may become predisposed to vaso-occlusive events.