T-lymphocyte reconstitution following rigorously T-cell-depleted versus unmodified autologous stem cell transplants

We compared the kinetics of T-cell recovery after extensive ex vivo and in vivo T-cell depleted autologous stem cell transplantation (SCT) for multiple sclerosis (MS; n=8) with unmodified SCT for hematological malignancies (HM; n=39). Both patient group showed a very protracted recovery of 'naive' CD4(+), 45R0(-) ( approximately CD45RA(+)) T-cells. Within the 'primed' CD4(+), 45R0(+) T-cells, the 'central memory' cells expressing the CD62L and CD27 markers were the slowest to recover. The repopulating T-cells were highly activated, as shown by increased expression of HLA-DR and the apoptosis marker CD95. The capability of CD4(+) and CD8(+) T-cells to produce IFN-gamma, IL-2 and TNF-alpha had reached normal ranges from 2 months post SCT onwards. Unexpectedly, the kinetics of T-cell recovery between 3 and 12 months post transplant was similar in T-depleted and unmodified SCT. Before SCT, the HM patients showed lymphopenia of all T-cell subsets, upregulated HLA-DR and CD95 expression and increased cytokine responses. We suggest that the similar kinetics of T-cell recovery in the two patient groups may be explained by the susceptibility to apoptosis of the activated CD4(+) T-cells in the autografts of the HM patients. This susceptibility to apoptosis would interfere with a swift and sustained CD4(+) T-cell regeneration post SCT.

Serum levels of the homeostatic B cell chemokine, CXCL13, are elevated during HIV infection

HIV infection is associated with B cell dysfunction, which includes B cell hyperactivation, hypergammaglobulinemia, impaired production of antibodies against specific antigens, and a loss of B cell memory. Because lymph node architecture is progressively destroyed during HIV infection, it is possible that normal B cell trafficking is impaired as well, which could be a cause or a result of these abnormalities. Because the homeostatic chemokine, CXCL13 (BLC, BCA-1), is a major regulator of B cell trafficking, we assessed circulating levels of this molecule in HIV infection. Serum levels of CXCL13 were seen to be progressively elevated in HIV disease. Serum levels of CXCL13 correlated strongly with those of the inflammation-associated chemokine, inducible protein-10 (IP-10), in subjects who had advanced HIV disease, and more moderately with levels of soluble CD30 (sCD30), sCD27, and sCD23. CXCL13 levels also correlated moderately with viral load and showed a significant decline after use of highly active antiretroviral treatment (HAART). Elevated levels of CXCL13 could cause impaired or altered trafficking of B cells during HIV infection and could contribute to the previously reported loss of CXCR5, the receptor for CXCL13, from the surface of circulating B cells in HIV infection.

Prolonged activation of virus-specific CD8+T cells after acute B19 infection

BACKGROUND

Human parvovirus B19 (B19) is a ubiquitous and clinically significant pathogen, causing erythema infectiosum, arthropathy, transient aplastic crisis, and intrauterine fetal death. The phenotype of CD8+ T cells in acute B19 infection has not been studied previously.

METHODS AND FINDINGS

The number and phenotype of B19-specific CD8+ T cell responses during and after acute adult infection was studied using HLA-peptide multimeric complexes. Surprisingly, these responses increased in magnitude over the first year post-infection despite resolution of clinical symptoms and control of viraemia, with T cell populations specific for individual epitopes comprising up to 4% of CD8+ T cells. B19-specific T cells developed and maintained an activated CD38+ phenotype, with strong expression of perforin and CD57 and downregulation of CD28 and CD27. These cells possessed strong effector function and intact proliferative capacity. Individuals tested many years after infection exhibited lower frequencies of B19-specific cytotoxic T lymphocytes, typically 0.05%-0.5% of CD8+ T cells, which were perforin, CD38, and CCR7 low.

CONCLUSION

This is the first example to our knowledge of an "acute" human viral infection inducing a persistent activated CD8+ T cell response. The likely explanation--analogous to that for cytomegalovirus infection--is that this persistent response is due to low-level antigen exposure. CD8+ T cells may contribute to the long-term control of this significant pathogen and should be considered during vaccine development.

Virus-induced polyclonal B cell activation improves protective CTL memoryvia retained CD27 expression on memory CTL

Different viruses elicit distinct phenotypes of memory cytotoxic T lymphocytes (CTL). This is reflected in differential expression of homing receptors and costimulatory molecules like CD27. Memory CTL retained CD27 following lymphocytic choriomeningitis virus (LCMV) infection, but not after immunization with recombinant vaccinia virus or tumor cells expressing LCMV glycoprotein. Stable CD27 expression on memory CTL required ligation by CD70 expressed on polyclonally activated B cells during the contraction phase. The functional consequence of CD27 expressed on virus-specific CTL was analyzed in CD27-deficient mice. LCMV infection of CD27(-/-) mice revealed that primary CTL activation and expansion as well as elimination of the virus were independent of CD27 expression. In contrast, ligation of CD27 on memory CTL upon secondary antigen encounter increased clonal expansion and improved protection against re-infection. This points to novel B cell-CTL interactions during viral infection and to a beneficial role of polyclonal B cell activation that represents a characteristic of murine LCMV, human immunodeficiency virus and human hepatitis B and C virus infection.

During viral infection of the respiratory tract, CD27, 4-1BB, and OX40 collectively determine formation of CD8+ memory T cells and their capacity for secondary expansion

Independent studies have shown that CD27, 4-1BB, and OX40 can all promote survival of activated CD8+ T cells. We have therefore compared their impact on CD8+ memory T cell formation and responsiveness within one, physiologically relevant model system. Recombinant mice, selectively lacking input of one or two receptors, were challenged intranasally with influenza virus, and the immunodominant virus-specific CD8+ T cell response was quantified at priming and effector sites. Upon primary infection, CD27 and (to a lesser extent) 4-1BB made nonredundant contributions to accumulation of CD8+ virus-specific T cells in draining lymph nodes and lung, while OX40 had no effect. Interestingly though, in the memory response, accumulation of virus-specific CD8+ T cells in spleen and lung critically depended on all three receptor systems. This was explained by two observations: 1) CD27, 4-1BB, and OX40 were collectively responsible for generation of the same memory CD8+ T cell pool; 2) CD27, 4-1BB, and OX40 collectively determined the extent of secondary expansion, as shown by adoptive transfers with standardized numbers of memory cells. Surprisingly, wild-type CD8+ memory T cells expanded normally in primed OX40 ligand- or 4-1BB ligand-deficient mice. However, when wild-type memory cells were generated in OX40 ligand- or 4-1BB ligand-deficient mice, their secondary expansion was impaired. This provides the novel concept that stimulation of CD8+ T cells by OX40 and 4-1BB ligand during priming imprints into them the capacity for secondary expansion. Our data argue that ligand on dendritic cells and/or B cells may be critical for this.

CD27/CFSE-based ex vivo selection of highly suppressive alloantigen-specific human regulatory T cells

Naturally occurring CD4(+)CD25(+) regulatory T cells (Treg) are crucial in immunoregulation and have great therapeutic potential for immunotherapy in the prevention of transplant rejection, allergy, and autoimmune diseases. The efficacy of Treg-based immunotherapy critically depends on the Ag specificity of the regulatory T cells. Moreover, the use of Ag-specific Treg as opposed to polyclonal expanded Treg will reduce the total number of Treg necessary for therapy. Hence, it is crucial to develop ex vivo selection procedures that allow selection and expansion of highly potent, Ag-specific Treg. In this study we describe an ex vivo CFSE cell sorter-based isolation method for human alloantigen-specific Treg. To this end, freshly isolated CD4(+)CD25(+) Treg were labeled with CFSE and stimulated with (target) alloantigen and IL-2 plus IL-15 in short-term cultures. The alloantigen-reactive dividing Treg were characterized by low CFSE content and could be subdivided by virtue of CD27 expression. CD27/CFSE cell sorter-based selection of CD27(+) and CD27(-) cells resulted in two highly suppressive Ag-specific Treg subsets. Each subset suppressed naive and Ag-experienced memory T cells, and importantly, CD27(+) Treg also suppressed ongoing T cell responses. Summarizing, the described procedure enables induction, expansion, and especially selection of highly suppressive, Ag-specific Treg subsets, which are crucial in Ag-specific, Treg-based immunotherapy.

Absence of surface CD27 distinguishes hairy cell leukemia from other leukemic B-cell malignancies

Surface expression of CD27 was evaluated in 75 mature leukemic B-cell neoplasms. All cases other than hairy cell leukemia (HCL) expressed CD27. Intensity was significantly higher in chronic lymphocytic leukemia. Lack of CD27 in 17/17 HCL contrasted with expression of this marker in 5/5 splenic lymphomas with villous lymphocytes. Lack of CD27 is a new distinctive feature of HCL among B-cell malignancies.

Generation of migratory antigen-specific plasma blasts and mobilization of resident plasma cells in a secondary immune response

Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19(+)/CD27(high)/intracellular immunoglobulin G(high) (IgG(high))/HLA-DR(high)/CD38(high)/CD20(-)/CD95(+) tetanus toxin-specific antibody-secreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19(+)/CD27(high)/intracellular IgG(high)/HLA-DR(low)/CD38(+)/CD20(-)/CD95(+) cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity.

Tumor rejection induced by CD70-mediated quantitative and qualitative effects on effector CD8+ T cell formation

In vivo priming of antigen-specific CD8+ T cells results in their expansion and differentiation into effector T cells followed by contraction into a memory T cell population that can be maintained for life. Recent evidence suggests that after initial antigenic stimulation, the magnitude and kinetics of the CD8+ T cell response are programmed. However, it is unclear to what extent CD8+ T cell instruction in vivo is modulated by costimulatory signals. Here, we demonstrate that constitutive ligation of the tumor necrosis factor receptor family member CD27 by its ligand CD70 quantitatively augments CD8+ T cell responses to influenza virus infection and EL-4 tumor challenge in vivo by incrementing initial expansion and maintaining higher numbers of antigen-specific T cells in the memory phase. Concomitantly, the quality of antigen-specific T cells improved as evidenced by increased interferon (IFN)-gamma production and a greater cytotoxic potential on a per cell basis. As an apparent consequence, the superior effector T cell formation induced by CD70 protected against a lethal dose of poorly immunogenic EL4 tumor cells in a CD8+ T cell- and IFN-gamma-dependent manner. Thus, CD70 costimulation enhances both the expansion and per cell activity of antigen-specific CD8+ T cells.

Loss of circulating CD27+ memory B cells and CCR4+ T cells occurring in association with elevated EBV loads in XLP patients surviving primary EBV infection

Detailed longitudinal studies of patients with X-linked lymphoproliferative disease (XLP) may increase our understanding of the immunologic defects that contribute to the development of lymphoma and hypogammaglobulinemia in XLP. We describe progressive changes observed in immunoglobulin concentrations, lymphocyte subsets, and Epstein-Barr virus (EBV) loads occurring in a 2-year period in a newly infected, but otherwise healthy, carrier (patient 9). We compare these findings with those observed in the patient's brother, who had hypogammaglobulinemia and XLP (patient 4). Immunoglobulin G (IgG), IgM, and IgA concentrations increased in patient 9 during acute EBV infection, but thereafter they decreased steadily to concentrations consistent with hypogammaglobulinemia, reaching a plateau 5 months after infection. In both patients, CD19+ B-lymphocyte rates remained lower than 3%, with a contraction of the B-cell memory compartment (CD27+ CD19+/CD19+) to 20% (normal range, 32%-56%). T-lymphocyte subpopulations showed a reduction in CD4+ T-cell counts and a permanent CD8+ T-cell expansion. Interestingly, CXCR3 memory TH1 cells were expanded and CCR4+ TH2 lymphocytes were reduced, suggesting that abnormal skewing of memory T-cell subsets might contribute to reduced antibody synthesis. Despite an expanded number of CD3+CD8+ lymphocytes, increased EBV loads occurred in both patients without overt clinical symptoms of mononucleosis, lymphoproliferative disease, or lymphoma.

HIV-1-Specific Memory CD4+ T Cells Are Phenotypically Less Mature Than Cytomegalovirus-Specific Memory CD4+ T Cells

HIV-1-specific CD4(+) T cells are qualitatively dysfunctional in the majority of HIV-1-infected individuals and are thus unable to effectively control viral replication. The current study extensively details the maturational phenotype of memory CD4(+) T cells directed against HIV-1 and CMV. We find that HIV-1-specific CD4(+) T cells are skewed to an early central memory phenotype, whereas CMV-specific CD4(+) T cells generally display a late effector memory phenotype. These differences hold true for both IFN-gamma- and IL-2-producing virus-specific CD4(+) T cells, are present during all disease stages, and persist even after highly active antiretroviral therapy (HAART). In addition, after HAART, HIV-1-specific CD4(+) T cells are enriched for CD27(+)CD28(-)-expressing cells, a rare phenotype, reflecting an early intermediate stage of differentiation. We found no correlation between differentiation phenotype of HIV-1-specific CD4(+) T cells and HIV-1 plasma viral load or HIV-1 disease progression. Surprisingly, HIV-1 viral load affected the maturational phenotype of CMV-specific CD4(+) T cells toward an earlier, less-differentiated state. In summary, our data indicate that the maturational state of HIV-1-specific CD4(+) T cells cannot be a sole explanation for loss of containment of HIV-1. However, HIV-1 replication can affect the phenotype of CD4(+) T cells of other specificities, which might adversely affect their ability to control those pathogens. The role for HIV-1-specific CD4(+) T cells expressing CD27(+)CD28(-) after HAART remains to be determined.

Clonotypic IgM V/D/J sequence analysis in Waldenstrom macroglobulinemia suggests an unusual B-cell origin and an expansion of polyclonal B cells in peripheral blood

Analysis of clonotypic immunoglobulin M (IgM) from 15 patients with Waldenstrom macroglobulinemia (WM) showed a strong preferential use of the VH3/JH4 gene families. Identification of the WM IgM V/D/J was validated using single-cell analysis, confirming its presence in most B cells. Despite the extensive hypermutated VH genes in 13 of 15 patients, statistical analysis of framework/complementary-determining region (FR/CDR) mutation patterns suggests that they might have escaped antigenic selection. Neither intraclonal diversity nor isotype switching was detectable. Membranous and secreted forms of clonotypic IgM transcripts were present in bone marrow and blood. Single-cell analysis showed that clonotypic B cells coexpress CD20, surface IgM (sIgM), and sIgD but that they lack CD138. Most B cells lacked memory marker CD27 despite their hypermutated variable regions otherwise suggestive of memory status. At diagnosis, circulating B cells in WM are largely clonotypic. However, when monoclonal IgM levels are decreased, clonotypic frequencies are substantially reduced despite elevated CD20+ cells, shown to be polyclonal by DNA sequencing and CDR3 fragment analysis. Thus, WM includes the expansion of circulating, polyclonal B cells. Overall, this work suggests that WM may originate from a largely VH3-restricted, somatically mutated, predominantly CD27(-)IgM(+)IgD+ population that cannot undergo class switching, suggestive of B cells that might have bypassed the germinal center.

CD40 Stimulation of Human Peripheral B Lymphocytes: Distinct Response from Naive and Memory Cells

During secondary immune response, memory B lymphocytes proliferate and differentiate into Ig-secreting cells. In mice, the binding of CD40 by CD154 clearly enhances the activation and differentiation of memory B lymphocytes. In humans, the role of CD40-CD154 in the stimulation of memory B lymphocytes is not as obvious since in vitro studies reported positive and negative effects on their proliferation and differentiation in Ig-secreting cells. In this study, we examine the response of peripheral memory and naive cells in relation to the duration of CD40-CD154 interaction. We measured the proliferation and differentiation of both subsets stimulated with CD154 and IL-4 for short- (4-5 days) and long-term (>7 days) periods. Following short-term stimulation, memory B lymphocytes did not expand but represented the only subset differentiating into IgG- and IgM-secreting cells. A longer stimulation of this population led to cell death, while promoting naive B lymphocyte proliferation, expansion, and differentiation into IgM- or IgG-secreting cells. This prolonged CD40 stimulation also triggered naive B lymphocytes to switch to IgG and to express CD27 even in absence of somatic hypermutation, suggesting that these latter events could be independent. This study suggests that naive and memory B lymphocytes have distinct requirements to engage an immune response, reflecting their different roles in humoral immunity.

OX40 ligation on activated T cells enhances the control of Cryptococcus neoformans and reduces pulmonary eosinophilia

Pulmonary eosinophilia induced in C57BL/6 mice after Cryptococcus neoformans infection is driven by CD4(+) Th2 cells. The immunological mechanisms that protect against eosinophilia are not fully understood. Interaction of OX40 (CD134) and its ligand, OX40L, has been implicated in T cell activation and cell migration. Unlike CD28, OX40 is only expressed on T cells 1-2 days after Ag activation. Manipulation of this pathway would therefore target recently activated T cells, leaving the naive repertoire unaffected. In this study, we show that engagement of OX40 by an OX40L:Ig fusion protein drives IFN-gamma production by CD4(+) T cells and reduces eosinophilia and C. neoformans burden in the lung. Using gene-depleted mice, we show that reduction of eosinophilia and pathogen burden requires IL-12 and/or IFN-gamma. C. neoformans infection itself only partially induces OX40L expression by APCs. Provision of exogenous OX40L reveals a critical role of this pathway in the prevention of C. neoformans-induced eosinophilia.

Mature CD8(+) T lymphocyte response to viral infection during fetal life

Immunization of newborns against viral infections may be hampered by ineffective CD8(+) T cell responses. To characterize the function of CD8(+) T lymphocytes in early life, we studied newborns with congenital human cytomegalovirus (HCMV) infection. We demonstrate that HCMV infection in utero leads to the expansion and the differentiation of mature HCMV-specific CD8(+) T cells, which have similar characteristics to those detected in adults. High frequencies of HCMV-specific CD8(+) T cells were detected by ex vivo tetramer staining as early as after 28 weeks of gestation. During the acute phase of infection, these cells had an early differentiation phenotype (CD28(-)CD27(+)CD45RO(+), perforin(low)), and they acquired a late differentiation phenotype (CD28(-)CD27(-)CD45RA(+), perforin(high)) during the course of the infection. The differentiated cells showed potent perforin-dependent cytolytic activity and produced antiviral cytokines. The finding of a mature and functional CD8(+) T cell response to HCMV suggests that the machinery required to prime such responses is in place during fetal life and could be used to immunize newborns against viral pathogens.

Increased expression of T cell activation markers (CD25, CD26, CD40L and CD69) in atherectomy specimens of patients with unstable angina and acute myocardial infarction

Atherosclerotic plaques contain a chronic immune mediated inflammation in which T cells play an important role. A previous study revealed that the numbers of interleukin-2 receptor-positive T cells is increased in culprit lesions of patients with acute coronary syndromes; a finding of considerable interest since it indicates a recent change in the intraplaque T cell mediated immune response. Confirmation of this observation is important, because it could provide insight into the onset of the acute event. We have, therefore, expanded our earlier work by using a panel of different T cell activation markers (CD25, CD26, CD40L, CD69). The study is based on 58 culprit lesions from patients who underwent coronary atherectomy. There were four groups of patients: chronic stable angina (n=13), stabilized unstable angina (n=16), refractory unstable angina (n=15), and acute myocardial infarction (AMI; n=14). Activated T cells were expressed as a percentage of the total of CD3-positive cells. CD25, CD26, CD40L, and CD69/CD3 percentages increased with the severity of the coronary syndrome. In patients with AMI all percentages were significantly higher than in patients with chronic stable angina. CD25, CD26, CD40L, and CD69/CD3 percentages in patients with an unstable condition (refractory unstable angina and AMI) were significantly higher than those in patients with a stable condition (chronic stable or stabilized unstable angina) The finding that the percentage of T cells with recent onset activation is significantly increased in the culprit lesions of patients with acute coronary syndromes suggests strongly that a recent change in pathogenic stimulation has occurred leading to local T cell activation.

Frequencies of circulating cytolytic, CD45RA+CD27-, CD8+ T lymphocytes depend on infection with CMV

Viral infections may cause serious disease unless the adaptive immune system is able to clear the viral agents through its effector arms. Recent identification and functional characterization of subpopulations of human CD8(+) T cells has set the stage to study the correlation between the appearance of particular subsets and common viral infections during childhood, i.e., EBV, CMV, varicella-zoster virus (VZV), and the attenuated measles-mumps-rubella (MMR) vaccine strains. In a cohort of 220 healthy children we analyzed lymphocytes and subpopulations of CD4(+) and CD8(+) T cells. The presence of the cytolytic CD45RA(+)CD27(-) subset of CD8(+) T cells correlated with prior CMV infection as defined by seroconversion (p < 0.0001). The number of this CD8(+) T cell subset remained stable during follow-up over 3 years in 40 children. The CD45RA(+)CD27(-) subset of CD8(+) T cells first appeared during acute CMV infection and subsequently stabilized at an individual set-point defined by age and immunocompetence. The functional importance of these cells in CMV surveillance was reflected by their increased numbers in immunosuppressed pediatric kidney transplant patients. Preferential expansion of CD8(+)CD45RA(+)CD27(-) cytolytic T cells seems unique for CMV.

Blood and intragraft CD27 gene expression in cardiac transplant recipients

The present study investigated gene expression of costimulatory molecule CD27 in relation to the occurrence of acute cardiac rejection. CD27 transcripts were measured by means of quantitative competitive reverse transcriptase-polymerase chain reaction in 120 endomyocardial biopsies and in 89 samples of blood mononuclear cells from 31 recipients. Higher levels of CD27 transcripts were observed in biopsies with rejection than in samples without rejection (medians, 7.1 and 1.9; P = 0.06). In contrast, blood mononuclear cells collected during rejection showed lower levels than blood mononuclear cells from rejection-free periods (medians, 3.3 vs. 7.9; P = 0.03). Considering only endomyocardial biopsies without rejection, the values were lower in samples from recipients who did not present any rejection during the first 6 months after transplantation than in those from recipients who had at least one rejection during the same period (medians, 0 vs. 3.5, P < 0.001; percentage of biopsies expressing CD27, 44% vs. 77%). In conclusion, the presence of intragraft CD27 mRNA may identify recipients at risk for developing acute rejection.

Accumulation of B lymphocytes with a naive, resting phenotype in a subset of hepatitis C patients

Chronic infection with hepatitis C virus (HCV) is associated with disturbances of B lymphocyte activation and function: autoantibody production, mixed cryoglobulinemia, and B cell lymphomas. It has been proposed that these abnormalities reflect chronic antigenic stimulation or aberrant signaling through the B cell coreceptor, the latter mediated by binding of the HCV E2 glycoprotein to CD81. To test this hypothesis, we measured expression of activation and differentiation markers on peripheral blood B cells from patients with chronic HCV infection. Thirty-six HCV patients with and without mixed cryoglobulinemia were compared with 18 healthy control volunteers and 17 sustained virologic responders who had cleared HCV infection. Ten of the 36 HCV patient samples showed increased B cell frequencies; B cell frequency was higher in patients with more severe hepatic fibrosis. However, these samples lacked evidence of Ag-driven activation or proliferation. The expanded cells were low in the activation markers CD25, CD69, CD71, CD80, and CD86. Proliferation of circulating B cells was unchanged in HCV patients. These cells did not express the differentiation marker CD27, suggesting that they were not enriched in memory B cells. Furthermore, the expanded B cells expressed both IgD and IgM, suggesting that they were antigenically naive. Together, these results indicate that B cell expansion in the peripheral blood of HCV patients is not associated with Ag-mediated activation and differentiation. Instead, factors other than antigenic stimulation may promote the accumulation of peripheral blood B cells with a naive phenotype in a subset of HCV patients.

Intrinsic differences in the proliferation of naive and memory human B cells as a mechanism for enhanced secondary immune responses

Humoral immune responses elicited after secondary exposure to immunizing Ag are characterized by robust and elevated reactivity of memory B cells that exceed those of naive B cells during the primary response. The mechanism underlying this difference in responsiveness of naive vs memory B cells remains unclear. We have quantitated the response of naive and memory human B cells after in vitro stimulation with T cell-derived stimuli. In response to stimulation with CD40 ligand alone or with IL-10, both IgM-expressing and Ig isotype-switched memory B cells entered their first division 20-30 h earlier than did naive B cells. In contrast, the time spent traversing subsequent divisions was similar. Consistent with previous studies, only memory cells differentiated to CD38(+) blasts in a manner that increased with consecutive division number. These differentiated CD38(+) B cells divided faster than did CD38(-) memory B cell blasts. Proliferation of CD40 ligand-stimulated naive B cells as well as both CD38(+) and CD38(-) cells present in cultures of memory B cells was increased by IL-10. In contrast, IL-2 enhanced proliferation of CD38(-) and CD38(+) memory B cell blasts, but not naive cells. Thus, memory B cells possess an intrinsic advantage over naive B cells in both the time to initiate a response and in the division-based rate of effector cell development. These differences help explain the accelerated Ab response exhibited by memory B cells after secondary challenge by an invading pathogen, a hallmark of immunological memory.

CD27 and CD40 inhibit p53-independent mitochondrial pathways in apoptosis of B cells induced by B cell receptor ligation

B cells in the germinal center are known to undergo apoptosis after B cell receptor (BCR) ligation, a process relevant to immunological tolerance. Human CD27 is a B cell co-stimulatory molecule. The aim of this study was to compare the effects of CD27 and CD40 signals on BCR-mediated apoptosis of B cells. BCR ligation activated mitochondrial apoptotic pathways including down-regulation of Bcl-X(L), dissipation of mitochondrial transmembrane potential, release of cytochrome c, and activation of caspase-9. Each of these effects was significantly inhibited by CD27 and CD40. Bik expression was weakly but significantly down-regulated by CD27 but up-regulated by CD40. BCR ligation resulted in p53 activation including its phosphorylation at Ser(15), nuclear translocation, and target gene p53AIP1 induction. CD27 and CD40 clearly suppressed these processes. Analyses that used dominant-negative p53 variants revealed a low but still substantial level of BCR-mediated apoptosis and intact mitochondria-mediated apoptotic pathway. These pathways were further inhibited by CD27 and CD40, although the cells showed no p53 phosphorylation or p53AIP1 expression. Our results suggested that, at the mitochondrial level, CD27 and CD40 co-stimulatory signals regulated the p53-amplified apoptotic pathway in B cells through the inhibition of p53-independent apoptotic pathway primarily induced by BCR ligation.

Pimecrolimus inhibits up-regulation of OX40 and synthesis of inflammatory cytokines upon secondary T cell activation by allogeneic dendritic cells

Pimecrolimus is a new non-steroidal inhibitor of T cell and mast cell activation. In the present study, we compared the potency of pimecrolimus and cyclosporin A (CyA) to inhibit cytokine synthesis of alloantigen-primed T cells and the expression of CD134 (OX40), an inducible co-receptor molecule thought to be critical for the survival and expansion of inflammation-mediating T cells. To mimic the physiological situation of recurrent antigenic stimulation, we have used dendritic cells (DC) as stimulators of purified CD4+ T cells in the primary and secondary allogeneic mixed lymphocyte culture (allo-MLC). Pimecrolimus inhibited surface expression of OX40 and prevented the up-regulation of CD25 and CD54 with a 10-fold higher potency compared to CyA. Similarly, 50% inhibition of allo-DC-mediated T cell proliferation by pimecrolimus was obtained at 0.55 nm, compared to about 12 nm for CyA. Furthermore, pimecrolimus blocked the increase of OX40 on primed T cells restimulated on day 10 in secondary allo-MLC. Allo-DC-primed T cells showed a restricted cytokine profile characterized by the production of TNF-alpha, IFN-gamma and IL-2 but low to undetectable levels of IL-4 and IL-10. The synthesis of TNF-alpha and IFN-gamma and the up-regulation of OX40 on T cells after secondary allogeneic stimulation were almost entirely blocked by 10 nm pimecrolimus. Taken together, pimecrolimus inhibits T cell proliferation and Th1 cytokine synthesis and also prevents the up-regulation of the OX40 co-receptor on primed T cells indicating its potential in the therapy of chronic inflammation and autoimmunity.

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.

Roles of IL-1 in the development of rheumatoid arthritis: consideration from mouse models

Expression of inflammatory cytokines is augmented in the joints of patients with rheumatoid arthritis (RA). We found that cytokine levels are also elevated in the joints of a mouse arthritis model, human T-cell leukemia virus type I (HTLV-I) transgenic (Tg) mouse. Depletion of IL-1 by gene targeting greatly reduced the incidence of the disease, indicating the importance of this cytokine in the development of arthritis. Furthermore, IL-1 receptor antagonist (IL-1Ra)-deficient mice develop autoimmunity and arthritis spontaneously. These observations suggest that excess IL-1 signaling the causes autoimmunity. We show that IL-1 activates the immune system non-specifically by inducing CD40L and OX40 co-signaling molecules on T cells. In this review, the roles of IL-1 in the development of autoimmunity and arthritis in mouse models will be discussed.