Differential signal transduction, membrane trafficking, and immune effector functions mediated by FcgammaRI versus FcgammaRIIa.

Receptors for the fragment crystallizable region of immunoglobulin-G (FcgammaRs) play an important role in linking the humoral and cellular arms of the immune response. In this study, we present a comprehensive functional comparison of 2 human Fc-receptors, FcgammaRI and FcgammaRIIa. Activation of FcgammaRI results in a novel signaling cascade that links phospholipase D1 to sphingosine kinase-1 in U937 cells and primary human monocytes. This induces the expression of proinflammatory mediators and is associated with trafficking of immune complexes into human leukocyte antigen-DM positive antigen-processing compartments coupled with improved MHC class II-mediated antigen presentation to T lymphocytes. In contrast, activation of FcgammaRIIa elicits signaling through phospholipase Cgamma1, resulting in increases in intracellular calcium, activation of nicotinamide adenine dinucleotide phosphate-oxidative burst, and differential membrane trafficking combined with impaired antigen presentation and proinflammatory cytokine expression. These data provide a mechanistic insight into the disparate activities associated with Fc receptors in immunity, namely, reinforcement of immune responses through stimulation of proinflammatory signaling and antigen presentation, versus the maintenance of immunologic homeostasis through the noninflammatory clearance of immune complexes.

Genome-wide gene expression profiling of human mast cells stimulated by IgE or FcepsilonRI-aggregation reveals a complex network of genes involved in inflammatory responses.

BACKGROUND: Mast cells are well established effectors of IgE-triggered allergic reactions and immune responses to parasitic infections. Recent studies indicate that mast cells may play roles in adaptive and innate immunity, suggesting an innovative view of the regulation of immune responses. Here, we profiled the transcriptome of human mast cells sensitized with IgE alone, or stimulated by FcepsilonRI aggregation. RESULTS: Our data show that among 8,793 genes examined, 559 genes are differentially regulated in stimulated mast cells when compared with resting/unstimulated mast cells. The major functional categories of upregulated genes include cytokines, chemokines, and other genes involved in innate and adaptive immune-responses. We observed the increased expression of over 63 gene-transcripts following IgE-sensitization alone. Our data was validated using Real-Time-PCR; ELISA and western blot. We confirmed that IgE alone does not trigger mast cell-immediate responses, such as calcium signals, degranulation or protein-phosphorylation. CONCLUSION: This report represents a substantial advance in our understanding of the genome wide effects triggered by "passive sensitization" or active stimulation of human mast cells, supporting mast cells' potential involvement in a wide range of inflammatory responses.

Expression profile of immune response genes in patients with Severe Acute Respiratory Syndrome.

BACKGROUND: Severe acute respiratory syndrome (SARS) emerged in later February 2003, as a new epidemic form of life-threatening infection caused by a novel coronavirus. However, the immune-pathogenesis of SARS is poorly understood. To understand the host response to this pathogen, we investigated the gene expression profiles of peripheral blood mononuclear cells (PBMCs) derived from SARS patients, and compared with healthy controls. RESULTS: The number of differentially expressed genes was found to be 186 under stringent filtering criteria of microarray data analysis. Several genes were highly up-regulated in patients with SARS, such as, the genes coding for Lactoferrin, S100A9 and Lipocalin 2. The real-time PCR method verified the results of the gene array analysis and showed that those genes that were up-regulated as determined by microarray analysis were also found to be comparatively up-regulated by real-time PCR analysis. CONCLUSIONS: This differential gene expression profiling of PBMCs from patients with SARS strongly suggests that the response of SARS affected patients seems to be mainly an innate inflammatory response, rather than a specific immune response against a viral infection, as we observed a complete lack of cytokine genes usually triggered during a viral infection. Our study shows for the first time how the immune system responds to the SARS infection, and opens new possibilities for designing new diagnostics and treatments for this new life-threatening disease.

Epstein-Barr virus-associated T/natural killer-cell lymphoproliferative disorder in children and young adults has similar molecular signature to extranodal nasal natural killer/T-cell lymphoma but shows distinctive stem cell-like phenotype.

We performed gene expression profiling in Epstein-Barr virus (EBV)-associated T/natural killer (NK)-cell lymphoproliferative disorder in children and young adults (TNKLPDC) in order to understand the molecular pathways deregulated in this disease and compared it with nasal-type NK/T-cell lymphoma (NKTL). The molecular and phenotypic signature of TNKLPDC is similar to NKTL, with overexpression of p53, survivin and EZH2. Down-regulation of EZH2 in TNKLPDC cell lines led to an increase in apoptosis and decrease in tumor viability, suggesting that EZH2 may be important for the survival of TNKLPDC cells and hence potentially a useful therapeutic target. Notably, our gene expression profiling revealed a distinctive enrichment of stem cell related genes in TNKLPDC compared to NKTL. This was validated by a significantly higher expression of aldehyde dehydrogenase 1 (ALDH1) in TNKLPDC cell lines compared to NKTL cell lines. The novel discovery of cancer stem cell properties in TNKLPDC has potential therapeutic implications in this group of disorders.

Clonogenic multiple myeloma cells have shared stemness signature associated with patient survival.

Multiple myeloma is the abnormal clonal expansion of post germinal B cells in the bone marrow. It was previously reported that clonogenic myeloma cells are CD138-. Human MM cell lines RPMI8226 and NCI H929 contained 2-5% of CD138- population. In this study, we showed that CD138- cells have increased ALDH1 activity, a hallmark of normal and neoplastic stem cells. CD138-ALDH+ cells were more clonogenic than CD138+ALDH- cells and only CD138- cells differentiated into CD138+ populations. In vivo tumor initiation and clonogenic potentials of the CD138- population was confirmed using NOG mice. We derived a gene expression signature from functionally validated and enriched CD138- clonogenic population from MM cell lines and validated these in patient samples. This data showed that CD138- cells had an enriched expression of genes that are expressed in normal and malignant stem cells. Differentially expressed genes included components of the polycomb repressor complex (PRC) and their targets. Inhibition of PRC by DZNep showed differential effect on CD138- and CD138+ populations. The 'stemness' signature derived from clonogenic CD138- cells overlap significantly with signatures of common progenitor cells, hematopoietic stem cells, and Leukemic stem cells and is associated with poorer survival in different clinical datasets.