B-cells and their targeting in rheumatoid arthritis--current concepts and future perspectives

Rheumatoid arthritis (RA) is a chronic, autoimmune disease that affects primarily the joints and without proper treatment results in their progressive destruction. In addition to T-cells, B-cells play a central role in the pathogenesis of this disease. The synovial tissue is an active site of B-cell accumulation, plasma cell differentiation and in situ antibody-production in RA. As part of the complex role of B-cells in the joints and synovial membrane of RA patients, B cells secrete chemokines and cytokines and may function as antigen presenting cells. The multifaceted pathogenic function of B-cells identifies them as excellent targets for immunosuppressive therapy. B-cell targeting involves a wide spectrum of molecules, for example the B-cell antigen CD20 that allows specific and effective B-cell depletion. Another target, CD79, expressed by B-cell and plasma cell precursors is an obvious candidate that induces apoptosis as well as inhibition of B-cell receptor (BCR) activation and possibly depletion of ectopic germinal centers (GC). Inhibition of B-cell co-stimulatory molecules such as CD40, CD80/86 and ICOS, can lead to diminished B-cell activation. Moreover, anti-chemokine and anti-cytokine therapies can be efficacious in RA by the disruption of B-cell activation and autoantibody production, B-cell synovial migration and ectopic GC formation. Finally, targeting the signal transduction pathways required for proximal BCR signaling has also been found efficacious in early clinical trials in RA. Even so, some B cells inhibit immune responses, these regulatory B cells may play a part in immune regulation in patients and it is unclear what effects B cell depletion strategies have in terms of such B cell subsets. This review discusses current strategies of targeting B-cells as therapeutic candidates in the management of RA. Better insights into the pathogenic role of B-cells provide efficacious opportunities to improve both therapy and prognosis of patients with RA.     

Primary cutaneous B-cell lymphoma with abundant reactive gamma/delta T-cells within the skin lesion and peripheral blood

T-cell/histiocyte-rich diffuse large B-cell lymphoma is characterized by abundant reactive T-cell and histiocyte infiltration within nodal diffuse large B-cell lymphoma, and only limited cases of primary cutaneous T-cell-rich B-cell lymphoma have been documented. These reactive T-cells usually show a T-helper phenotype. Gamma/delta T-cell is a functionally distinct T-cell lineage, which constitutes on average 5% of all T-cells in the peripheral blood. Herein, we report the first documented case of primary cutaneous malignant B-cell lymphoma with abundant reactive gamma/delta⁺ T-cells within the skin lesion and peripheral blood. An 80-year-old Japanese male presented with a gradually enlarged knee nodule. Histopathological study revealed diffuse infiltration of lymphoid cells in the dermis and subcutis. Proliferation of large-sized atypical lymphoid cells was observed among medium-sized lymphocytes with convoluted nuclei. Immunohistochemically, these large-sized atypical lymphocytes were CD20⁺, and relatively many gamma/delta⁺ cell infiltration was also noted. Flowcytometric analysis revealed deviation of lambda+ cells (lambda/kappa 58) and increase of CD3⁺ gamma/delta⁺ cells (6%). Peripheral blood had CD3⁺ gamma/delta⁺ cells (28.8%). Rearrangement of immunoglobulin heavy chain, but not of T-cell receptor beta and gamma chains, was observed. Accordingly, an ultimate diagnosis of cutaneous B-cell lymphoma with abundant reactive gamma/delta⁺ cells was made. Recent studies have shown reactive gamma/delta⁺ T-cell infiltration and/or elevation in the peripheral blood in patients with various types of carcinoma, and that they play a role in the pathogenesis of some carcinomas. Therefore, additional analysis is needed to clarify the role of reactive gamma/delta⁺ T-cells in malignant lymphoma.     

T-cell/histiocyte-rich large B-cell lymphoma is a disseminated aggressive neoplasm: differential diagnosis from Hodgkin's lymphoma

AIMS: An accurate diagnosis of T-cell/histiocyte-rich large B-cell lymphoma needs to take into consideration those forms of Hodgkin's lymphoma also characterized by a predominance of small lymphocytes and histiocytes, i.e. nodular lymphocyte predominance Hodgkin's lymphoma and lymphocyte-rich classical Hodgkin's lymphoma. We have studied the clinical, phenotypic and genetic features of a series of 12 cases of T-cell/histiocyte-rich large B-cell lymphoma along with 18 cases of Hodgkin's lymphoma for comparative purposes. METHODS AND RESULTS: Of the Hodgkin's lymphoma cases, there were 11 lymphocyte predominance type and seven classic type. T-cell/histiocyte-rich large B-cell lymphomas presented usually in advanced stages (III or IV in 11/12 cases), frequently with 'B' symptoms (6/9 cases), and followed a more aggressive course than Hodgkin's lymphoma (4/8 patients died due to the tumour in T-cell/histiocyte-rich large B-cell lymphoma versus 0/15 in Hodgkin's lymphoma). T-cell/histiocyte-rich large B-cell lymphoma cases showed diffuse effacement of the nodal architecture by a proliferation of scattered large atypical B-cells obscured by a background of small T-lymphocytes (more CD8+, TIA1+ than CD57+). Five cases showed also a prominent histiocytic component. The large B-cells expressed CD45 and often EMA (6/10 cases). On the other hand, CD 30, CD15 and latent infection by Epstein-Barr virus (EBV) were generally lacking. bc l6 and CD10 were, respectively, detected in 6/6 and 1/5 cases. Conventional polymerase chain reaction (PCR) showed monoclonal immunoglobulin heavy chain (IgH) gene rearrangements in all T-cell/histiocyte-rich large B-cell lymphomas studied (5/5), but did not detect any case with t(14;18) involving the major breakpoint region (0/4). CONCLUSIONS: The differential diagnosis of T-cell/histiocyte-rich large B-cell lymphoma from Hodgkin's lymphoma is facilitated by the integration of different immunophenotypic, molecular and clinical findings. T-cell/histiocyte-rich large B-cell lymphoma is a monoclonal neoplasm of bc l6+ B-cells with a phenotypic profile similar to lymphocyte predominance Hodgkin's lymphoma, suggesting a germinal centre origin and a possible relation to this disease. Therefore, in order to distinguish it from lymphocyte predominance Hodgkin's lymphoma, characterization of the reactive background, IgH gene rearrangement studies by conventional PCR and clinical features are more useful. In contrast, T-cell/histiocyte-rich large B-cell lymphoma can be distinguished from classical Hodgkin's lymphoma thanks to the presence of monoclonal IgH rearrangement and the CD 30-CD15-CD45+EMA+ immunophenotypic profile of the neoplastic cells in T-cell/histiocyte-rich large B-cell lymphoma.     

Advantages of targeting B cell receptor complex to treat B-cell derived autoimmune diseases and lymphomas

Antibodies produced by B-cells provide protection from infectious agents. However, impaired cell death signaling pathways in B-cells can lead to cancer, immunodeficiency or autoimmune diseases. B-cell signaling molecules such as CD20, CD19, Btk, and BAFF-R are targeted by therapeutic drugs and used to treat B-cell derived lymphomas or autoimmune diseases. Nevertheless, B-cells could develop resistance to these therapeutic drugs or the therapeutic drugs may have off-target effects. For instance, repeated rituximab (anti-CD20 antibody) treatment may lead to the loss of its target cell surface molecule, CD20. In addition, in B-cell malignancies, loss of CD19 expression has been observed. Another target molecule, Btk is expressed not only in B-cells but also in mast cells, macrophages, and dendritic cells. Thus, targeting Btk could negatively regulate the functions of innate immunity. The expression of BAFF-R is thought to be restricted to B-cells but it is also expressed on T-cells. Targeting BAFF-R, therefore, may lead to depletion of T-cells in addition to B-cells. B cell receptor (BCR) expression and signaling, however, are critically important for development, differentiation and survival of B-cells. Moreover, BCR is exclusively expressed on B-cells, which makes it an excellent target to avoid off-target effects.     

B-cell receptor: from resting state to activate

B-cell activation is triggered by the binding of antigen to the B-cell receptor (BCR). The early molecular events triggered by BCR binding of ligand have been well-characterized both biochemically and using optical microscopy techniques to visualize B-cell activation as it happens. However, we understand much less about the BCR before activation. For this reason, this review will address recent advances in our view of the structure, organization and dynamics of the resting, unstimulated BCR. These parameters have important implications for our understanding of the initiation of B-cell activation and will be discussed in the context of current models for BCR activation. These models include the conformation-induced oligomerization model, in which binding of antigen to monomeric BCR induces a pulling or twisting force causing conformational unmasking of a clustering interface in the Cμ4 domain. Conversely, the dissociation activation model proposes that BCRs exist in auto-inhibitory oligomers on the resting B-cell surface and binding of antigen promotes the dissociation of the BCR oligomer exposing phosphorylation residues within Igα/Igβ. Finally, the collision coupling model suggests that BCR are segregated from activating co-receptors or kinases and activation is associated with changes in BCR mobility on the cell surface, which allows for the functional interaction of these elements.     

Low CD4+ T-cell counts in HIV patients receiving effective antiretroviral therapy are associated with CD4+ T-cell activation and senescence but not with lower effector memory T-cell function

The adverse effects of immune activation on CD4(+) T-cell recovery and the relationship between CD4(+) T-cell counts and effector T-cell function were examined in HIV-1 patients receiving long-term effective ART. Patients with nadir CD4(+) T-cell counts <100/microl, > 12 months on ART and >6 months with <50 HIV RNA copies/ml were stratified by current CD4(+) T-cell counts and patients from the lowest (n = 15) and highest (n = 12) tertiles were studied. We assessed proliferation (Ki67), activation (HLA-DR, CD38) and replicative senescence (CD57) by flow cytometry and CD4(+) T-cell responses to CMV by IFN-gamma ELISpot. Proportions of CD4(+) T-cells expressing HLA-DR or CD57 were strong univariate predictors of total (P = 0.0002 and P = 0.002) and naive (P < 0.0001 and P < 0.0001, respectively) CD4(+) T-cell counts, suggesting that CD4(+) T-cell activation drives the depletion of naive CD4(+) T-cells. This was clearest in patients with a small/undetectable thymus. IFN-gamma responses to CMV were similar in patients with low or high CD4(+) T-cell counts.     

FK506 attenuates thymic output in patients with myasthenia gravis

Introduction

Myasthenia gravis (MG) is an antibody-mediated, T-cell-dependent autoimmune disease. The symptoms are caused by high-affinity IgG against the muscle acetylcholine receptor (AChR) at the neuromuscular junction. The production of these antibodies in B-cells depends on AChR-specific CD4⁺ T-cells and the thymus gland seems to play a significant role in the pathogenesis of MG. Altered thymic T-cell export seems to be associated with a pathological mechanism in myasthenia gravis. Tacrolimus (FK506) has recently been used to treat MG.

Material and methods

We examined the effects of tacrolimus on thymic T-cell export in patients with MG. Sixteen patients with nonthymomatous and/or thymectomized MG were treated with oral administrations of tacrolimus. To assess the effect of tacrolimus on the thymic output, we assayed the levels of T-cell receptor excision circle (TREC), a molecular marker of thymus emigrants.

Results

T-cell receptor excision circle was not significantly different from those in age-matched controls before tacrolimus therapy, but they were partially decreased 4 months after tacrolimus therapy. T-cell receptor excision circle levels were significantly decreased in the thymomatous group (p < 0.05), but not in the nonthymomatous group. Tacrolimus treatment significantly attenuated TREC levels in cultured CD4^–CD8⁺ cells (p < 0.05), but total cell counts were not significantly changed.

Conclusions

These results indicate that TREC levels may become a marker of the curative effect of tacrolimus therapy for thymomatous MG, and that tacrolimus suppresses not only activating T-lymphocytes, but also naïve T-cells.     

Histiocyte-rich, T-cell-rich B-cell lymphoma: a distinct diffuse large B-cell lymphoma subtype showing characteristic morphologic and immunophenotypic features

AIMS: The clinicopathological features of histiocyte-rich, T-cell-rich B-cell lymphoma (HRTR-BCL) were first recognized in 1992. In this study, 60 cases of HRTR-BCL were analysed in order to provide a detailed morphological and immunophenotypical profile of the disorder. METHODS AND RESULTS: HRTR-BCL is easily distinguished from other B-cell lymphomas rich in stromal T-cells by (i) a diffuse or vaguely nodular growth pattern, (ii) the presence of a minority population of CD15-, CD20+ large neoplastic B-cells, (iii) a prominent stromal component composed of both T-cells and non-epithelioid histiocytes, and (iv) the scarcity of small reactive B-cells. These criteria also enable a reliable distinction from lymphocyte-rich classical Hodgkin's lymphoma (CHL), from lymphocyte-predominant Hodgkin's lymphoma (LPHL), paragranuloma type and from peripheral T-cell lymphoma. Based on the morphology of the neoplastic cells and on their frequent bcl-6 immunoreactivity, we speculate that HRTR-BCL may be derived from a progenitor cell of germinal centre origin. CONCLUSIONS: HRTR-BCL presents characteristic clinical features, affecting predominantly middle-aged men who present with advanced stage disease and are at high risk of treatment failure. Considering these distinctive clinicopathological features, recognizing HRTR-BCL as a lymphoma entity may be justified.     

Loss of HIV-specific memory B-cells as a potential mechanism for the dysfunction of the humoral immune response against HIV

A central, yet unresolved issue in the pathogenesis of HIV disease is the mechanism of antibody perturbation. In this study, HIV-specific memory B-cells were quantified in groups of infected subjects and compared with memory responses to other antigens and antibody titers. HIV-specific memory B-cell responses were vigorous in individuals with CD4⁺ T-cell counts > 350/μl and weak or undetectable in subjects with CD4⁺ T-cell numbers < 200/μl. Memory B-cell loss was permanent, because antiretroviral therapy failed to restore HIV-specific memory responses while influenza- and tetanus toxoid-specific memory B-cells remained unaffected or recovered. Antibody titers to Gag strongly correlated with memory B-cell frequencies. In contrast, Env-specific antibodies were maintained in advanced disease despite low or undetectable levels of memory B-cells. These results provide a potential mechanism by which destruction of HIV-specific CD4⁺ T-cells affects the humoral immune response against HIV and compromises the ability to maintain an effective antibody response.     

B-cell Activation versus Tolerance - The Central Role of Immunoglobulin Receptor Engagement and T-cell Help

The critical variables responsible for the decision between activation and tolerance in the B-cell compartment were studied in the well-characterised hen egg lysozyme: antilysozyme transgenic model. Mature B-cells exposed to a low antigenic signal, which resulted in a receptor occupancy of between 5% and 25%, remained ‘indifferent’ (i.e. were neither activated nor tolerant), had a normal lifespan and recirculated through B-cell follicles. When receptor occupancy reached a critical threshold of approximately 50%, the B-cells became activated and moved to the outer T-cell zones where they died. This threshold appeared to be lower in the case of immature B-cells. On addition of T-cell help, however, the B-cells were rescued, proliferated and secreted antibody. Thus the outcome of the interaction between B-cells and antigen (self or foreign) is determined largely by the degree of antigen receptor engagement and availability of T-cell help.     

CD5+ T-cell/histiocyte-rich large B-cell lymphoma.

CD5 expression in neoplastic large B-cells in T-cell/histiocyte-rich large B-cell lymphoma has not been reported, to the best of our knowledge. Here we describe the first case of CD5+ T-cell/histiocyte-rich large B-cell lymphoma that is well documented by histomorphology, immunohistochemistry, flow cytometry immunophenotyping and sorting, and immunoglobulin heavy-chain gene rearrangement study by polymerase chain reaction. The expression of CD5 in large neoplastic B-cells was demonstrated by immunohistochemistry and multicolor flow cytometry. The clonal nature of the CD5+ neoplastic B-cells was confirmed by rearranged immunoglobulin heavy (IgH) chain with polymerase chain reaction (PCR) of flow cytometry-sorted CD5+/CD19+/kappa+ cells. The CD5+ neoplastic large B-cells expressed bcl-6 and MUM1/IRF4 but not CD138 by immunohistochemistry. This suggests that the neoplastic cells may be of late germinal-center B-cell/ early post-germinal center B-cell origin. The patient responded to chemotherapy, CHOP (Cytoxan, doxorubicin, vincristine, and prednisone), and Rituxan very well and is currently in complete remission clinically. We propose that the current case, CD5+ T-cell/histiocyte-rich large B-cell lymphoma, represents a variant of recently reported de novo CD5+ diffuse large B-cell lymphomas. Our patient has had an excellent response to treatment; however, the clinical and biologic significance of CD5 expression in T-cell/histiocyte-rich large B-cell lymphoma requires further studies. Awareness of the CD5+ T-cell/histiocyte-rich large B-cell lymphoma variant will prompt pathologists to perform CD5 immunohistochemical stain in cases of T-cell/histiocyte-rich large B-cell lymphoma. This will lead to identifying more cases to understand the clinical and biologic characteristics of this variant.     

Viral interactions with B-cells contribute to increased regulatory T-cells during chronic HCV infection

Hepatitis C virus (HCV) has a propensity to establish chronic infection that is characterized by attenuated virus-specific T-cell responses. Mechanisms leading to T-cell attenuation are poorly understood and likely involve dysfunctional interactions between antigen-presenting cells (APC) and effector/regulatory T-cells. Reports on dendritic cells (DC) have described only minor dysfunction during HCV infection. However, there is a paucity of reports regarding B-cell function, despite clear associations with B-cell-related secondary sequelae. In this study we evaluated the state of B-cells during chronic HCV infection, and observed a diminished ability to respond to mitogenic stimuli, correlating with increased apoptosis. This was in contrast to their ex vivo phenotype, which indicated ongoing chronic activation in vivo. There was a high association of HCV-positive strand RNA with B-cells in a subset of HCV patients. Interestingly, ex-vivo-derived HCV RNA-positive B-cells induced significantly greater proliferation in allogeneic T-cells than in HCV-negative B-cells, correlating with an increased generation of CD4(+)CD25(+)FOXP3(+) regulatory T-cells (Tregs). In-vitro exposure of healthy peripheral blood mononuclear cells (PBMC) to HCV resulted in robust activation of resting B-cells. These HCV-exposed B-cells also showed an enhanced ability to generate Tregs. Our results provide strong evidence for a novel and paradoxical link between HCV-induced enhanced APC function and the generation of Tregs.     

Primary T-cell rich B-cell lymphoma of the common bile duct

A 34-year-old woman was hospitalized for the investigation of a one-month history of intestinal disorders, gastric heaviness and transitory icteric episodes. Extensive clinical investigations suggested the diagnosis of gall bladder carcinoma or sclerosing cholangitis. At laparotomy, the proximal part of common bile duct was markedly thickened by a white, firm, fish-flesh like tumour extending in to the cystic duct, gall bladder wall and to the liver. Histological study showed a diffuse lymphoid proliferation of the common bile duct mainly composed of small cells mixed with scattered large atypical cells. Immunohistochemistry revealed that most of the small cells expressed T-cell markers with predominant CD 4 and - T-cell receptors and without phenotypic gap, whereas large atypical cells showed monotypic B phenotype with co-expression of and heavy chains and light chain restriction. No evidence of primary nodal lymphoma was found during extensive clinical, radiological, sonographic or scanographic examinations. Sequential chemotherapy (MACOP-B) was instituted and the patient was still alive 4 years after diagnosis. Morphological and immunohistochemistry findings fulfilled criteria for a primary high grade B-cell lymphoma (centroblastic type, Kiel classification) from common bile duct concealed by numerous small reactive T-cells, so called T-cell rich B-cell lymphoma, not previously described in this location.     

Activation of CD4+ and CD8+ lymphocyte subsets by streptozotocin in the popliteal lymph node assay. II. Comparison with acute graft-vs-host reaction in H-2 incompatible F1 mouse hybrids.

Changes in lymphocyte subsets during an acute GVH reaction were compared to STZ-induced PLN response in mice. The GVH reaction was induced locally by sc injection of parental C57Bl/6 [B6] spleen cells into (C57Bl/6 x DBA/2) F1 footpad [B6D2F1]. Early cell activation and time-related changes in T- and B-lymphocyte subsets were monitored during the onset of the GVH reaction by flow cytometry and immunophenotyping. Examination of cell size and chromatin decondensing for T- and B-cell subsets showed differences in activation profile during the early phase of the GVH reaction. The present study provides direct evidence for early in vivo activation of both CD4+ and CD8+ T-cells. Our data confirm the central role of T-cell activation in the induction of a GVH reaction and suggest that recirculatory host B-cells can play an important role in early GVH node enlargement. Overall, our comparative analysis supports the concept of polyclonal T-cell activation for both STZ-related and GVH-induced lymphoproliferation. Chemicals-induced lymphoproliferation leading to autoimmune reactions is a challenging issue. A number of drugs and chemicals have been tested in the PLNA assay for lymphoproliferative potential. We previously reported the activation and proliferation of T-cell subsets following STZ injection into murine footpads. The STZ-induced PLN enlargement and proliferation characteristics of T- and B-cell subsets were postulated to be similar to those of an acute allogeneic GVHR. In the present study, a cytometric analysis of T- and B-cell subsets in PLNs was performed during an acute allogeneic GVHR, for comparison purposes. Such a reaction results in a massive node enlargement five to ten times that seen after stimulation with conventional antigens. Acute GVHR is believed to be a direct consequence of the high frequency of alloreactive donor T-cells inducing a massive proliferation of B-cells, almost exclusively of host origin, in GVHR nodes. It is now widely accepted that donor T-cells activated as the result of exposure to foreign MHC antigens in the recipient, secrete various cytokines which assist the host B-cells and bypass the normal B-T cell cooperation. Induction of an acute GVHR, as in the parental B6--->recipient B6D2F1 model, requires the injection of CD4+ and CD8+ donor T-cells into an F1 recipient that differs from the parent at both MHC class I and II loci.(ABSTRACT TRUNCATED AT 400 WORDS)     

Aberrant T-cell antigen receptor-mediated responses in autoimmune lymphoproliferative syndrome

Autoimmune Lymphoproliferative Syndrome (ALPS) is a disorder of defective lymphocyte apoptosis due to mutations of the Fas receptor and other molecules in the Fas signaling pathway. In addition to accumulation of CD4(-) CD8(-) double-negative (DN) T cells, many patients display a dysregulated cytokine pattern with dysfunctional T cells, suggesting Fas defects may impact pathways of T-cell activation/differentiation. Here, we report two novel mutations in the Fas receptor resulting in an ALPS phenotype. Utilizing flow cytometry, we found anti-CD3 activated CD4(+) T cells from these patients were incapable of fully upregulating activation markers (CD25, CD69, and CD40L) or producing interferon-gamma and IL-2. Additionally, DN T cells were unable to transduce proximal T-cell antigen receptor signals or produce cytokines. Furthermore, DN T cells overexpressed CD57 and phenotypically resembled end-stage effector cells. As DN T cells were essentially anergic, the clinical manifestations of autoimmunity are more likely to be a consequence of aberrant cytokine secretion within the CD4(+) T-cell subpopulation.     

Visualizing a role for the actin cytoskeleton in the regulation of B-cell activation

Summary: Appropriate activation of B cells is required for mounting protective humoral immune responses. B-cell activation is initiated following specific recognition of antigen by the B-cell receptor (BCR) and results in the generation of antibody-secreting plasma cells and long-lived memory cells. Initial imaging approaches revealed that B cells undergo dramatic molecular and morphological reorganizations following recognition of antigen. A number of these studies pointed to a role for the underlying cytoskeleton in regulating early events of B-cell activation. More recently, groundbreaking advances in imaging technologies have enabled direct visualization of the role for the cytoskeleton in regulating events at the B-cell membrane. Indeed, we have demonstrated that an ezrin-defined actin network shapes BCR diffusion and signaling both in the resting state and following antigen-induced activation. Importantly, alongside these in vitro imaging approaches, it has been demonstrated that mutations in cytoskeleton regulators such as CD19, dedicator of cytokinesis 8 (DOCK8), and Wiskott-Aldrich syndrome protein (WASp) are often associated with antibody deficiency syndromes in humans, establishing the importance of cytoskeleton reorganizations in conferring effective adaptive immunity.     

Response differences between human CD4(+) and CD8(+) T-cells during CD28 costimulation: implications for immune cell-based therapies and studies related to the expansion of double-positive T-cells during aging

Since CD28 costimulation is critical for T-cell activation, there is great interest in CD28 as a target for immuntherapeutic approaches. We show that stimulation of human CD4(+) and CD8(+) T-cells differs in their responsiveness to stimulation with anti-CD3/CD28-coated beads, as surrogate antigen-presenting cells. While the CD4(+) subset responded with sustained proliferation, CD8(+) T-cells grew for a limited period only and failed to produce IL-2 beyond the first few days in culture. This decrease is accompanied with an increased rate of apoptosis in CD8(+) T-cells despite Bcl-x(L) expression. The CD8(+) but not the CD4(+) subset developed a reversible double-positive phenotype during CD28 costimulation. This finding may have some bearing on the appearance of double-positive T-cells in human peripheral blood. This double-positive subset was shown to undergo a statistically significantly increase during aging in humans. Taken together, the above data have important implications for immunotherapy and immune senescence.     

SLAP, a regulator of immunoreceptor ubiquitination, signaling, and trafficking

Summary:  Src-like adapter proteins (SLAP and SLAP-2) constitute a family of proteins that are expressed in a variety of cell types but are studied most extensively in lymphocytes. They have been shown to associate with proximal components of the T-cell receptor (TCR) and B-cell receptor (BCR) signaling complexes. An interaction of SLAP with c-Cbl leads to the ubiquitination and degradation of phosphorylated components of the TCR- and BCR-signaling complexes. The absence of this process in immature SLAP-deficient T and B cells leads to increased immunoreceptor levels due to decreased intracellular retention and degradation. We propose a model in which SLAP-dependent regulation of immunoreceptor levels allows for finer control of immunoreceptor signaling. Thus, SLAP functions to dampen immunoreceptor signaling, thereby influencing lymphocyte development and repertoire selection.