A respiratory chain controlled signal transduction cascade in the mitochondrial intermembrane space mediates hydrogen peroxide signaling.

Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) govern cellular homeostasis by inducing signaling. H2O2 modulates the activity of phosphatases and many other signaling molecules through oxidation of critical cysteine residues, which led to the notion that initiation of ROS signaling is broad and nonspecific, and thus fundamentally distinct from other signaling pathways. Here, we report that H2O2 signaling bears hallmarks of a regular signal transduction cascade. It is controlled by hierarchical signaling events resulting in a focused response as the results place the mitochondrial respiratory chain upstream of tyrosine-protein kinase Lyn, Lyn upstream of tyrosine-protein kinase SYK (Syk), and Syk upstream of numerous targets involved in signaling, transcription, translation, metabolism, and cell cycle regulation. The active mediators of H2O2 signaling colocalize as H2O2 induces mitochondria-associated Lyn and Syk phosphorylation, and a pool of Lyn and Syk reside in the mitochondrial intermembrane space. Finally, the same intermediaries control the signaling response in tissues and species responsive to H2O2 as the respiratory chain, Lyn, and Syk were similarly required for H2O2 signaling in mouse B cells, fibroblasts, and chicken DT40 B cells. Consistent with a broad role, the Syk pathway is coexpressed across tissues, is of early metazoan origin, and displays evidence of evolutionary constraint in the human. These results suggest that H2O2 signaling is under control of a signal transduction pathway that links the respiratory chain to the mitochondrial intermembrane space-localized, ubiquitous, and ancient Syk pathway in hematopoietic and nonhematopoietic cells.

Cytoplasmic Ig alpha serine/threonines fine-tune Ig alpha tyrosine phosphorylation and limit bone marrow plasma cell formation.

Igα serine 191 and 197 and threonine 203, which are located in proximity of the Igα ITAM, dampen Igα ITAM tyrosine phosphorylation. In this study, we show that mice with targeted mutations of Igα S191, 197, and T203 displayed elevated serum IgG2c and IgG2b concentrations and had elevated numbers of IgG2c- and IgG2b-secreting cells in the bone marrow. BCR-induced Igα tyrosine phosphorylation was slightly increased in splenic B cells. Our results suggest that Igα serine/threonines limit formation of IgG2c- and IgG2b-secreting bone marrow plasma cells, possibly by fine-tuning Igα tyrosine-mediated BCR signaling.

Utility of CD200 immunostaining in the diagnosis of primary mediastinal large B cell lymphoma: comparison with MAL, CD23, and other markers.

CD200, an immunoglobulin superfamily membrane glycoprotein, is expressed in a number of B cell lymphoproliferative disorders, including primary mediastinal large B cell lymphoma, but not diffuse large B cell lymphoma, based on a preliminary study. Here, we compare the expression of CD200 with other markers of primary mediastinal large B cell lymphoma, including MAL and CD23, in formalin-fixed, paraffin-embedded histologic sections from a series of 35 cases of primary mediastinal large B cell lymphoma and 30 cases of diffuse large B cell lymphoma. CD200 exhibits the greatest staining sensitivity of the markers studied: 94%, compared with CD23 (69%), MAL (86%), TRAF (86%), and REL (77%). It exhibits staining specificity of 93%, similar to that of CD23 (93%) and MAL (97%), and greater than that of TRAF (77%) and REL (83%). We conclude that CD200 is a practical and useful marker for the diagnosis of primary mediastinal large B cell lymphoma.

Complement regulator CD59 protects against angiotensin II-induced abdominal aortic aneurysms in mice.

BACKGROUND: Complement system, an innate immunity, has been well documented to play a critical role in many inflammatory diseases. However, the role of complement in the pathogenesis of abdominal aortic aneurysm, which is considered an immune and inflammatory disease, remains obscure. METHODS AND RESULTS: Here, we evaluated the pathogenic roles of complement membrane attack complex and CD59, a key regulator that inhibits the membrane attack complex, in the development of abdominal aortic aneurysm. We demonstrated that in the angiotensin II-induced abdominal aortic aneurysm model, deficiency of the membrane attack complex regulator CD59 in ApoE-null mice (mCd59ab(-/-)/ApoE(-/-)) accelerated the disease development, whereas transgenic overexpression of human CD59 (hCD59(ICAM-2+/-)/ApoE(-/-)) in this model attenuated the progression of abdominal aortic aneurysm. The severity of aneurysm among these 3 groups positively correlates with C9 deposition, and/or the activities of MMP2 and MMP9, and/or the levels of phosphorylated c-Jun, c-Fos, IKK-alpha/beta, and p65. Furthermore, we demonstrated that the membrane attack complex directly induced gene expression of matrix metalloproteinase-2 and -9 in vitro, which required activation of the activator protein-1 and nuclear factor-kappaB signaling pathways. CONCLUSIONS: Together, these results defined the protective role of CD59 and shed light on the important pathogenic role of the membrane attack complex in abdominal aortic aneurysm.

RUNX transcription factors: association with pediatric asthma and modulated by maternal smoking.

Intrauterine smoke exposure (IUS) is a strong risk factor for development of airways responsiveness and asthma in childhood. Runt-related transcription factors (RUNX1-3) have critical roles in immune system development and function. We hypothesized that genetic variations in RUNX1 would be associated with airway responsiveness in asthmatic children and that this association would be modified by IUS. Family-based association testing analysis in the Childhood Asthma Management Program genome-wide genotype data showed that 17 of 100 RUNX1 single-nucleotide polymorphisms (SNPs) were significantly (P < 0.03-0.04) associated with methacholine responsiveness. The association between methacholine responsiveness and one of the SNPs was significantly modified by a history of IUS exposure. Quantitative PCR analysis of immature human lung tissue with and without IUS suggested that IUS increased RUNX1 expression at the pseudoglandular stage of lung development. We examined these associations by subjecting murine neonatal lung tissue with and without IUS to quantitative PCR (N = 4-14 per group). Our murine model showed that IUS decreased RUNX expression at postnatal days (P)3 and P5 (P < 0.05). We conclude that 1) SNPs in RUNX1 are associated with airway responsiveness in asthmatic children and these associations are modified by IUS exposure, 2) IUS tended to increase the expression of RUNX1 in early human development, and 3) a murine IUS model showed that the effects of developmental cigarette smoke exposure persisted for at least 2 wk after birth. We speculate that IUS exposure-altered expression of RUNX transcription factors increases the risk of asthma in children with IUS exposure.

Complement regulator CD59 protects against atherosclerosis by restricting the formation of complement membrane attack complex.

Complement is a central effector system within the immune system and is implicated in a range of inflammatory disorders. CD59 is a key regulator of complement membrane attack complex (MAC) assembly. The atherogenic role of terminal complement has long been suspected but is still unclear. Here, we demonstrate that among mice deficient in apolipoprotein (Apo)E, the additional loss of murine CD59 (mCd59ab(-/-)/ApoE(-/-)) accelerated advanced atherosclerosis featuring occlusive coronary atherosclerosis, vulnerable plaque, and premature death and that these effect could be attenuated by overexpression of human CD59 in the endothelium. Complement inhibition using a neutralizing anti-mouse C5 antibody attenuated atherosclerosis in mCd59ab(-/-)/ApoE(-/-) mice. Furthermore, MAC mediated endothelial damage and promoted foam cell formation. These combined results highlight the atherogenic role of MAC and the atheroprotective role of CD59 and suggest that inhibition of MAC formation may provide a therapeutic approach for the treatment of atherosclerosis.

Characteristic expression patterns of TCL1, CD38, and CD44 identify aggressive lymphomas harboring a MYC translocation.

The distinction between Burkitt (BL) or atypical Burkitt/Burkitt-like lymphomas harboring a MYC translocation (MYC+) and diffuse large B-cell lymphomas (DLBCLs) with high proliferation fractions but without a MYC translocation (MYC-) can be difficult using standard morphologic and immunohistochemical criteria. Recently, unique gene expression profiles differentiating BL and DLBCL were reported and include higher transcript levels of T-cell leukemia-1 (TCL1) and CD38 and lower transcript levels of CD44 in MYC+ BL relative to MYC- DLBCL. We examined a cohort of 67 cytogenetically defined aggressive lymphomas using immunohistochemical techniques for expression of TCL1, CD38, and CD44 and found distinct expression patterns between MYC+ and MYC- tumors. Furthermore, these markers are better predictors of MYC status than combined staining for CD10 and BCL2. Thus staining for TCL1, CD38, and CD44 are useful ancillary tests to identify B-cell tumors for which confirmatory cytogenetic and/or fluorescent in situ hybridization studies assessing the status of the MYC locus should be pursued.

SYK kinase mediates brown fat differentiation and activation.

Brown adipose tissue (BAT) metabolism influences glucose homeostasis and metabolic health in mice and humans. Sympathetic stimulation of ß-adrenergic receptors in response to cold induces proliferation, differentiation, and UCP1 expression in pre-adipocytes and mature brown adipocytes. Here we show that spleen tyrosine kinase (SYK) is upregulated during brown adipocyte differentiation and activated by ß-adrenergic stimulation. Deletion or inhibition of SYK, a kinase known for its essential roles in the immune system, blocks brown and white pre-adipocyte proliferation and differentiation in vitro, and results in diminished expression of Ucp1 and other genes regulating brown adipocyte function in response to ß-adrenergic stimulation. Adipocyte-specific SYK deletion in mice reduces BAT mass and BAT that developed consisted of SYK-expressing brown adipocytes that had escaped homozygous Syk deletion. SYK inhibition in vivo represses ß-agonist-induced thermogenesis and oxygen consumption. These results establish SYK as an essential mediator of brown fat formation and function.

Programmed death-1 (PD-1) is a marker of germinal center-associated T cells and angioimmunoblastic T-cell lymphoma.

Programmed death-1 (PD-1), a member of the CD28 costimulatory receptor family, is expressed by germinal center-associated T cells in reactive lymphoid tissue. In a study of a wide range of lymphoproliferative disorders, neoplastic T cells in 23 cases of angioimmunoblastic lymphoma were immunoreactive for PD-1, but other subtypes of T cell and B cell non-Hodgkin lymphoma, as well as classic Hodgkin lymphoma, did not express PD-1. The pattern of PD-1 immunostaining of neoplastic cells in angioimmunoblastic lymphoma was similar to that reported for CD10, a recently described marker of neoplastic T cells in angioimmunoblastic lymphoma. Tumor-associated follicular dendritic cells in cases of angioimmunoblastic lymphoma were found to express PD-L1, the PD-1 ligand. In addition, PD-1-positive reactive T cells formed rosettes around neoplastic L&H cells in 14 cases of nodular lymphocyte predominant Hodgkin lymphoma studied. These findings, along with data from previous studies, suggest that angioimmunoblastic lymphoma is a neoplasm of germinal center-associated T cells and that there is an association of germinal center-associated T cells and neoplastic cells in nodular lymphocyte predominant Hodgkin lymphoma. PD-1 is a useful new marker for angioimmunoblastic lymphoma and lends further support to a model of T-cell lymphomagenesis in which specific subtypes of T cells may undergo neoplastic transformation and result in specific, distinct histologic, immunophenotypic, and clinical subtypes of T-cell neoplasia.

Histochemical analyses of altered fetal lung development following single vs multiple courses of antenatal steroids.

A single course of antenatal steroids is widely used during preterm labor to promote fetal lung maturation. However, little is known regarding efficacy and safety of multiple courses of antenatal steroids. In animal models and clinical trials, treatment with glucocorticoids can inhibit growth. The present study of single- vs multiple-course steroids in pregnant ewes analyzes the effects of steroids vs placebo on fetal lung histopathology. Single-course groups received dexamethasone (Dex) 6 mg or normal saline every 12 hr for 48 hr at 104-106 days of gestation (term = 150 days). Multiple-course groups received the first course at 76-78 days; this was repeated weekly for 5 weeks. At 108 days, lungs were analyzed using immunohistochemistry for alpha-smooth muscle actin, a myofibroblast marker and proliferating cell nuclear antigen. Cell injury/death was evaluated using TdT-mediated dUTP digoxigenin nick end labeling (TUNEL) analysis. Although fetal growth was restricted by either single or multiple courses of Dex, alveolar development was accelerated as measured by mean linear intercepts. Alveolar walls were thinner, developing septa were longer, and septal myofibroblasts were increased for both Dex groups compared with controls. Cell proliferation increased following multiple steroid courses, especially in the distal parenchyma, with a corresponding decrease in apoptosis. These observations suggest that Dex promotes alveolarization, whether given in single or multiple courses.

T-bet, a T cell-associated transcription factor, is expressed in Hodgkin's lymphoma.

T-bet, a T-box transcription factor, is expressed in CD4+ T lymphocytes committed to Th1 T-cell development and may participate in immunoglobulin class switching in B lymphocytes. T-bet is also expressed in a subset of T-cell lymphomas, particularly those that express other markers of Th1 T cell differentiation, and in a subset of B-cell non-Hodgkin's lymphomas. Because of the evidence that Hodgkin's lymphoma is a neoplasm of B cells, we examined cases of Hodgkin's lymphoma for T-bet expression by immunohistochemical staining and found that neoplastic cells in most cases of classic Hodgkin's lymphoma (33 of 37 cases, 89%), including nodular sclerosis type (17 of 21 cases, 81%) and mixed cellularity type (15 of 15, 100%), express T-bet. Neoplastic cells in most cases of nodular lymphocyte-predominant Hodgkin's lymphoma (15 of 18, 83%), a distinct clinical entity that differs from classic Hodgkin's lymphoma, also express T-bet. A Hodgkin's lymphoma-derived cell line, L1236, expresses T-bet by Western blot analysis as well as by immunohistochemical staining. In contrast, almost all cases of diffuse large B-cell lymphoma and most cases of anaplastic large cell lymphoma, neoplasms that may be confused with Hodgkin's lymphoma, are negative for T-bet. On that basis, T-bet should serve as a useful new marker for the diagnosis of Hodgkin's lymphoma. In addition, because T-bet expression is not detectable in the majority of reactive B cells, including germinal-center B cells, but is characteristically expressed by the neoplastic cells in Hodgkin's lymphoma, thought to be derived from germinal-center B cells, T-bet may play a role in Hodgkin's lymphoma oncogenesis.

The CD45 isoform B220 identifies select subsets of human B cells and B-cell lymphoproliferative disorders.

The B220 isoform of CD45, a pan B-cell marker in mice, is expressed by only a subset of human B cells that do not express the memory B-cell marker CD27, suggesting that it is a differentiation-specific isoform of CD45. We examined normal human peripheral blood B cells, secondary lymphoid tissue, and a range of human B-cell lymphoproliferative disorders for the expression of B220 by flow cytometric immunophenotyping and immunohistochemical staining. We found that a subset of human B cells in peripheral blood is positive for B220 by flow cytometric immunophenotypic analysis. In reactive lymphoid tissues, B220 is expressed by B cells occupying the mantle zones and by a subpopulation of germinal center cells, but, in contrast, marginal zone B cells in the spleen do not express B220. Of 94 cases of B-cell lymphoproliferative disorders, 33 (35%) were positive for B220 by flow cytometric immunophenotypic analysis, including most cases of marginal zone lymphoma, follicular lymphoma, and lymphoplasmacytic lymphoma. In contrast, all cases of precursor B lymphoblastic leukemia/lymphoma, mantle cell lymphoma, and chronic lymphocytic leukemia/small lymphocytic lymphoma were negative for B220. Immunohistochemical staining for B220 correlated with flow cytometric analysis for all cases studied by both methods. Our data demonstrate that B220 is expressed in a select subset of normal, reactive B cells in a pattern that is consistent with a marker of naive B cells. However, this restricted expression pattern is not seen in B-cell lymphoproliferative disorders. Discordance between the B220 expression patterns of normal mantle and marginal zone B cells and their respective neoplastic counterparts may aid in the distinction between normal and neoplastic proliferations at these anatomical sites.

Mucin core peptide expression can help differentiate Barrett's esophagus from intestinal metaplasia of the stomach.

It is important to distinguish Barrett's esophagus (BE) from intestinal metaplasia related to carditis because these conditions have a different natural history, risk of malignancy, and treatment. However, the distinction between these entities is difficult both clinically and pathologically. The aim of this study was to evaluate and compare the immunostaining pattern of five mucin core polypeptides in BE to cases of carditis or antritis with intestinal metaplasia. Routinely processed mucosal biopsies from 22 patients with intestinal-type BE, 24 patients with cardia intestinal metaplasia (10 Helicobacter pylori positive), 17 patients with antral intestinal metaplasia (all H. pylori positive), 20 control patients with a normal antrum, and 22 control patients with a normal cardia were immunostained with monoclonal antibodies against MUC1, MUC2, MUC3, MUC5AC, and MUC6 mucin core polypeptides. Staining was evaluated separately for goblet cells and non-goblet columnar cells and compared between all groups. A significantly higher number of BE cases (P < 0.05) showed goblet cell staining for MUC1 (55%) or MUC6 (32%) compared with patients with carditis with intestinal metaplasia (MUC1 14%, MUC6 7%) or antritis with intestinal metaplasia (MUC1 6%, MUC6 0%). BE also showed a higher frequency of MUC1 and MUC6 positivity in non-goblet columnar cells compared with carditis and antritis cases with intestinal metaplasia. Only cases of BE showed combined MUC1 and MUC6 staining (sensitivity 23%, specificity 100%). The sensitivity and specificity of MUC1 staining for BE are 55% and 96%, respectively, and for MUC6 staining 30% and 96%, respectively. Interestingly, normal gastric cardia mucosa also showed a significantly higher prevalence of MUC2 and MUC3 expression in glandular epithelium (29% and 38%, respectively) compared with the antrum (0% for both markers) (P < 0.05). In conclusion, MUC1 and MUC6 expression in BE is distinct from that of the cardia and antrum with intestinal metaplasia; thus, immunophenotyping for these markers may have some value in a subset of patients in helping to separate BE from patients with intestinal metaplasia of the cardia. Columnar epithelium in the "normal" gastric cardia has a partially intestinalized phenotype and, as a result, may represent an early form of metaplastic epithelium.

CD69 expression correlates with expression of other markers of Th1 T cell differentiation in peripheral T cell lymphomas.

CD69, a marker of early T cell activation, is associated with Th1 T cell differentiation. Previously we found that peripheral T cell lymphomas could be subdivided based on the expression of markers of Th1 versus Th2 differentiation, including CXCR3, CD134/OX40, CCR4, and CD30. Here we report immunohistochemical staining for CD69 in frozen and paraffin sections of peripheral T cell lymphomas that exhibit immunoreactivity for markers of Th1 or Th2 differentiation. CD69 expression correlated with immunoreactivity for other Th1 differentiation markers in 18 of 19 frozen specimens of peripheral T cell lymphomas (P = 0.0005). In 10 of these cases in which paraffin-embedded tissue was available for study, CD69 immunohistochemical staining of paraffin sections correlated with frozen section expression. CD69 immunostaining was performed on paraffin sections from 53 additional cases of peripheral T cell lymphoma and correlated with immunoreactivity for other Th1 differentiation markers (P < 0.0001) and was associated with specific subtypes of peripheral T cell lymphoma, including angioimmunoblastic lymphoma, Lennert's lymphoma, and mycosis fungoides/Sezary syndrome, previously noted to express Th1 differentiation-associated markers. Anaplastic large cell lymphoma, both systemic and cutaneous, which typically exhibits immunoreactivity for markers of Th2 expression, was negative for CD69 immunostaining in 22 of 24 cases. CD69 immunostaining results support previous findings that a subset of T cell lymphomas exhibits immunophenotypic features of either Th1 or Th2 T cell differentiation. In addition, CD69 is a useful immunohistochemical marker for specific T cell lymphomas in frozen and paraffin-embedded tissue.

CCR6 is a functional chemokine receptor that serves to identify select B-cell non-Hodgkin's lymphomas.

Several recent studies have revealed important contributions of chemokines and their receptors to the development and progression of both hematopoietic and nonhematopoietic neoplasms. The chemokine receptor CCR6 is unusual in that it mediates leukocyte chemotaxis in response to a single chemokine, CCL20 (macrophage inhibitory factor-3alpha), as well as in response to a family of antimicrobial peptides termed "beta-defensins." CCR6 is critical for mucosal immunity, and expression of the receptor is tightly regulated on hematopoietic cells. Here we characterize the expression of CCR6 on B cells and B-cell non-Hodgkin's lymphomas. We demonstrate that CCR6 expression is limited to cells comprising the mantle and marginal zones of the secondary lymphoid tissues and serves to identify the majority of mantle cell, marginal zone, and mucosa-associated lymphoid tissue lymphomas. Furthermore, we show that CCR6 serves as a functional chemokine receptor when expressed by neoplastic cells. Finally, we establish that the cognate ligand for CCR6 is present on mucosal epithelium infiltrated by neoplastic cells in select extranodal lymphomas. Thus, CCR6 is a useful new marker identifying a subset of B-cell non-Hodgkin's lymphomas and likely contributes to the localization of select extranodal lymphomas at mucosal sites.

CXCR4/CD184 immunoreactivity in T-cell non-Hodgkin lymphomas with an overall Th1- Th2+ immunophenotype.

We performed an immunohistochemical analysis of CXCR4/CD184 expression in frozen and paraffin-embedded sections of human peripheral T-cell lymphomas that exhibit a composite Th1 T-cell-like or Th2 T-cell-like immunophenotype, based on expression of Th1-associated markers (CXCR3, OX40/CD134, and CD69) and Th2-associated markers (CD30 and CCR4). In 66 cases examined, CXCR4/CD184 expression correlated significantly with immunoreactivity for other markers of Th2 differentiation (P < .0001). Anaplastic large cell lymphoma, which typically expresses markers of Th2 differentiation, was immunoreactive for CXCR4/CD184 in 22 (88%) of 25 cases. Tumors previously identified as exhibiting a composite Th1-like immunophenotype, which include angioimmunoblastic lymphoma, lymphoepithelioid lymphoma, and other peripheral T-cell lymphomas now termed unspecified, were positive for CXCR4/CD184 in 7 (17%) of 41 cases. These results are consistent with previous findings that a subset of peripheral T-cell lymphomas can be divided into Th1-like and Th2-like categories based on immunoreactivity with a limited set of markers. Our findings also suggest that CXCR4/CD184, which is expressed by a number of malignant neoplasms and may have a role in tumor metastasis, may have a similar function in CXCR4+ T-cell non-Hodgkin lymphomas.

T-bet, a T-cell-associated transcription factor, is expressed in a subset of B-cell lymphoproliferative disorders.

T-bet, a T-box transcription factor, is expressed in CD4+ T lymphocytes committed to Th1 T-cell development and in a subset of T-cell non-Hodgkin lymphomas. Recent evidence indicates that T-bet also is expressed in B lymphocytes and might participate in immunoglobulin class switching. We examined T-bet expression in 116 cases of B-cell lymphoproliferative disorders by immunostaining and found that T-bet was expressed consistently in precursor B-cell lymphoblastic leukemia/lymphoblastic lymphoma (14/14 cases) in contrast with precursor T-cell lymphoblastic leukemia/lymphoblastic lymphoma, which is consistently T-bet- (13 cases), as previously reported. T-bet is expressed in memory B cell-derived neoplasms (chronic lymphocytic leukemia, marginal zone lymphoma, hairy cell leukemia; 35/42 cases) but not in cases of mantle cell, follicular, and large cell lymphoma (43 cases). Expression of T-bet in precursor B-cell lymphoblastic leukemia/lymphoblastic lymphoma was confirmed by Western blot analysis. The expression of T-bet in a significant subset of B-cell lymphoproliferative disorders but not in the vast majority of reactive B cells suggests it might have a role in the oncogenesis of T-bet+ B-cell neoplasms. In addition, T-bet should serve as a useful new marker for the diagnosis and subtyping of B-cell lymphoproliferative disorders.

Differential expression of T-bet, a T-box transcription factor required for Th1 T-cell development, in peripheral T-cell lymphomas.

We studied T-bet expression in 91 cases of peripheral T-cell lymphoma (PTCL) by immunostaining and found expression in 42 cases (46%), including all 5 lymphoepithelioid lymphoma cases and 12 (86%) of 14 angioimmunoblastic lymphoma cases, but only 9 (25%) of 36 anaplastic large cell lymphoma cases. Expression of T-bet in PTCL correlates with expression of other markers of Th1 T-cell differentiation, including CXCR3 (P < .0001), CD69 (P = .0013), LEF-1 (P = .0007), and OX40/CD134 (P = .005), and absence of expression of markers of Th2 T-cell differentiation, including CD30 (P = .0001) and CXCR4 (P = .0144). Of 22 cases of PTCL immunoreactive for all Th1-associated markers previously studied and nonreactive for Th2-associated markers, 20 (91%) were immunoreactive for T-bet. Of 22 PTCL cases immunoreactive for Th2-associated markers studied and nonreactive for all Th1-associated markers studied, 4 (18%) were immunoreactive for T-bet. The remaining 47 PTCL cases (52%) exhibited incomplete or mixed staining for Th1- and Th2-associated markers, with 18 (38%) of 47 immunoreactive for T-bet. T-bet is a new marker that may contribute to the diagnosis and subtyping of PTCLs. T-bet expression in these neoplasms provides further support for a model of PTCL in which tumor subsets express markers of, and may be derived from, Th1- or Th2-committed T cells.

CD148 and CD27 are expressed in B cell lymphomas derived from both memory and naïve B cells.

CD148 and CD27 are activation antigens involved in B cell and T cell activation and development. They have been recently proposed as markers of normal human memory B cells corresponding to the presence of somatically hypermutated IgV genes. We undertook an immunohistochemical study of CD148 and CD27 expression on neoplastic B cells in 116 cases of B cell non-Hodgkin's lymphoma. All cases of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma, Burkitt's lymphoma, and the vast majority of cases of marginal zone B cell lymphoma and most cases of plasmacytoma/myeloma expressed CD148 and CD27. Follicular lymphoma and diffuse large B cell lymphoma were also immunoreactive for CD148 and CD27 with some variation and discordance in expression. Cases of precursor B-lymphoblastic lymphoma/leukemia did not express CD148 or CD27. Our findings demonstrate that CD148 and CD27 are expressed in a wide range of B cell non-Hodgkin's lymphomas, and, therefore, do not serve to distinguish between neoplastic cells of naïve and memory B cell derivation.

HP-1γ Controls High-Affinity Antibody Response to T-Dependent Antigens.

In vitro observations suggest a role for the mouse heterochromatin protein 1γ (HP-1γ) in the immune system. However, it has not been shown if and how HP-1γ contributes to immunity in vivo. Here we show that in mice, HP-1γ positively regulates the germinal center reaction and high-affinity antibody response to thymus (T)-dependent antigens by limiting the size of CD8(+) regulatory T-cell (Treg) compartment without affecting progenitor B- or T-cell-development. Moreover, HP-1γ does not control cell proliferation or class switch recombination. Haploinsufficiency of cbx-3 (gene encoding HP-1γ) is sufficient to expand the CD8(+) Treg population and impair the immune response in mice despite the presence of wild-type HP-1α and HP-1ß. This is the first in vivo evidence demonstrating the non-redundant role of HP-1γ in immunity.