Systemic antibodies can inhibit mouse mammary tumor virus-driven superantigen response in mucosa-associated lymphoid tissues.

Many mucosal pathogens invade the host by initially infecting the organized mucosa-associated lymphoid tissue (o-MALT) such as Peyer's patches or nasal cavity-associated lymphoid tissue (NALT) before spreading systemically. There is no clear demonstration that serum antibodies can prevent infections in o-MALT. We have tested this possibility by using the mouse mammary tumor virus (MMTV) as a model system. In peripheral lymph nodes or in Peyer's patches or NALT, MMTV initially infects B lymphocytes, which as a consequence express a superantigen (SAg) activity. The SAg molecule induces the local activation of a subset of T cells within 6 days after MMTV infection. We report that similar levels of anti-SAg antibody (immunoglobulin G) in serum were potent inhibitors of the SAg-induced T-cell response both in peripheral lymph nodes and in Peyer's patches or NALT. This result clearly demonstrates that systemic antibodies can gain access to Peyer's patches or NALT.

A non-random chromosome abnormality found in precursor-B lineage acute lymphoblastic leukaemia: dic(9;20)(p1?3;q11).

A comparison of cytogenetical data on acute lymphoblastic leukaemia studied at four large European centres has revealed a non-random dicentric chromosome abnormality: dic(9;20) (p1?3;q11) in 10 patients, nine of whom were children. All had early precursor-B lineage ALL, and eight children had a non-standard risk clinical presentation. The origin of the dicentric chromosome was demonstrated using a range of chromosome banding techniques. This was confirmed by FISH using paints and centromeric probes for chromosomes 9 and 20, together with a number of cosmid probes. The follow-up time of these patients is presently too short and the number of patients too few to determine the prognostic significant of this chromosome abnormality.

TNF deficiency fails to protect BAFF transgenic mice against autoimmunity and reveals a predisposition to B cell lymphoma.

TNF is well characterized as a mediator of inflammatory responses. TNF also facilitates organization of secondary lymphoid organs, particularly B cell follicles and germinal centers, a hallmark of T-dependent Ab responses. TNF also mediates defense against tumors. We examined the role of TNF in the development of inflammatory autoimmune disorders resembling systemic lupus erythematosus and Sjögren's syndrome induced by excess B cell-activating factor belonging to the TNF family (BAFF), by generating BAFF-transgenic (Tg) mice lacking TNF. TNF(-/-) BAFF-Tg mice resembled TNF(-/-) mice, in that they lacked B cell follicles, follicular dendritic cells, and germinal centers, and have impaired responses to T-dependent Ags. Nevertheless, TNF(-/-) BAFF-Tg mice developed autoimmune disorders similar to that of BAFF-Tg mice. Disease in TNF(-/-) BAFF-Tg mice correlates with the expansion of transitional type 2 and marginal zone B cell populations and enhanced T-independent immune responses. TNF deficiency in BAFF-Tg mice also led to a surprisingly high incidence of B cell lymphomas (>35%), which most likely resulted from the combined effects of BAFF promotion of neoplastic B cell survival, coupled with lack of protective antitumor defense by TNF. Thus, TNF appears to be dispensable for BAFF-mediated autoimmune disorders and may, in fact, counter any proneoplastic effects of high levels of BAFF in diseases such as Sjögren's syndrome, systemic lupus erythematosus, and rheumatoid arthritis.

Dectin-1 is essential for reverse transcytosis of glycosylated SIgA-antigen complexes by intestinal M cells.

Intestinal microfold (M) cells possess a high transcytosis capacity and are able to transport a broad range of materials including particulate antigens, soluble macromolecules, and pathogens from the intestinal lumen to inductive sites of the mucosal immune system. M cells are also the primary pathway for delivery of secretory IgA (SIgA) to the gut-associated lymphoid tissue. However, although the consequences of SIgA uptake by M cells are now well known and described, the mechanisms whereby SIgA is selectively bound and taken up remain poorly understood. Here we first demonstrate that both the Cα1 region and glycosylation, more particularly sialic acid residues, are involved in M cell-mediated reverse transcytosis. Second, we found that SIgA is taken up by M cells via the Dectin-1 receptor, with the possible involvement of Siglec-5 acting as a co-receptor. Third, we establish that transcytosed SIgA is taken up by mucosal CX3CR1⁺ dendritic cells (DCs) via the DC-SIGN receptor. Fourth, we show that mucosal and systemic antibody responses against the HIV p24-SIgA complexes administered orally is strictly dependent on the expression of Dectin-1. Having deciphered the mechanisms leading to specific targeting of SIgA-based Ag complexes paves the way to the use of such a vehicle for mucosal vaccination against various infectious diseases.

Activated B cells express functional Fas ligand.

Fas ligand (FasL, Apo-1L) is a member of the tumor necrosis factor protein family and binding to its receptor (Fas, Apo-1, CD95) triggers cell death through apoptosis. Ligand expression is restricted to cells with known cytolytic activity and found on hematopoietic cells of the T cell and natural killer lineage. Here we provide evidence that B lymphocytes can express FasL. Flow cytometric analysis revealed that FasL is expressed on the surface of B cells upon stimulation with either lipopolysaccharide or phorbol 12-myristate 13-acetate/ionomycin. FasL expression on activated B cells was confirmed by western blot and reverse transcriptase polymerase chain reaction analysis. FasL on B cells is functional since lipopolysaccharide-activated B lymphocytes derived from wild type, but not from gld mutant mice, were able to kill Fas-sensitive target cells. Our data suggest that the Fas system may contribute to the control of B cell homeostasis.

Specific fibroblastic niches in secondary lymphoid organs orchestrate distinct Notch-regulated immune responses.

Fibroblast-like cells of secondary lymphoid organs (SLO) are important for tissue architecture. In addition, they regulate lymphocyte compartmentalization through the secretion of chemokines, and participate in the orchestration of appropriate cell-cell interactions required for adaptive immunity. Here, we provide data demonstrating the functional importance of SLO fibroblasts during Notch-mediated lineage specification and immune response. Genetic ablation of the Notch ligand Delta-like (DL)1 identified splenic fibroblasts rather than hematopoietic or endothelial cells as niche cells, allowing Notch 2-driven differentiation of marginal zone B cells and of Esam(+) dendritic cells. Moreover, conditional inactivation of DL4 in lymph node fibroblasts resulted in impaired follicular helper T cell differentiation and, consequently, in reduced numbers of germinal center B cells and absence of high-affinity antibodies. Our data demonstrate previously unknown roles for DL ligand-expressing fibroblasts in SLO niches as drivers of multiple Notch-mediated immune differentiation processes.

MHC class II expression is differentially regulated in plasmacytoid and conventional dendritic cells.

Major histocompatibility complex (MHC) class II-restricted antigen presentation is essential for the function of dendritic cells (DCs). We show here that plasmacytoid DCs (pDCs) differ from all other DC subsets with respect to expression of CIITA, the 'master regulator' of MHC class II genes. The gene encoding CIITA is controlled by three cell type-specific promoters: pI, pIII and pIV. With gene targeting in mice, we demonstrate that pDCs rely strictly on the B cell promoter pIII, whereas macrophages and all other DCs depend on pI. The molecular mechanisms driving MHC class II expression in pDCs are thus akin to those operating in lymphoid rather than myeloid cells.

Lymphoid stroma in health and disease

Summary Secondary lymphoid organs (SLOB), such as lymph nodes and spleen, are the sites where primary immune responses are initiated. T lymphocytes patrol through the blood and SLOs on the search for pathogens which are presented to them as antigens by dendritic cells. Stromal cells in the Tzone - so called T zone fibroblastic reticular cells (TRCs) -are critical in organizing the migration of T cells and dendritic cells by producing the chemoattractants CCL19 and CCL21 and by forming a network which T cells use as a guidance system. They also form a system of small channels or conduits that allow rapid transport of small antigen molecules or cytokines from the subcapsular sinus to high endothelial venules. The phenotype and function of TRCs have otherwise remained largely unknown. We found a critical role for lymph node access in CD4+ and CD8+ T cell homeostasis and identified TRCs within these organs as the major source of interleukin-7 (IL-7). IL-7 is an essential survival factor for naïve T lymphocytes of which the cellular source in the periphery had been poorly defined. In vitro, TRC were able to prevent the death of naïve T but not of B lymphocytes by secreting IL-7 and the CCR7 ligand CCL 19. Using gene-targeted mice, we show anon-redundant function of CCL19 in T cell homeostasis. The data suggest that TRCs regulate T cell numbers by providing a limited reservoir of survival factors for which T cells have to compete. They help to maintain a diverse T cell repertoire granting full immunocompetence. To determine whether TRCs also play a role in pathology, we characterized so-called tertiary lymphoid organs (TLOs) that often develop at sites of chronic inflammation. We show that TLOs resemble lymph nodes or Peyer's patches not only with regard to lymphoid cells. TLOs formed extensive TRC networks and a functional conduit system in all three marine inflammation models tested. In one model we dissected the cells and signals leading to the formation of these structures. We showed that they critically depend on the presence of lymphotoxin and lymphoid tissue inducer cells. TRCs in TLOs also produce CCL19, GCL21 and possibly IL-7 which are all involved in the development of TLOs. Stromal cells therefore play a central role in the onset and perpetuation of chronic inflammatory diseases and could be an interesting target for therapy. Résumé Le système immunitaire est la défense de notre corps contre toutes sortes d'infections et de tumeurs. II est constitué de différentes populations de lymphocytes qui patrouillent constamment le corps à la recherche de pathogène. Parmi eux, les lymphocytes T et B passent régulièrement dans les organes lymphoïdes secondaires (SLO) qui sont les sites d'initiation de la réponse immunitaire. Les lymphocytes T sont recrutés du sang aux SLO où ils cherchent leur antigène respectif présenté par des cellules dendritiques. Des cellules stromales dans la zone T -nommées fibroblastic reticular cells' (TRC) -sécrètent des chimiokines CCL19 et CCL21 et ainsi facilitent les rencontres entre lymphocytes T et cellules dendritiques. De plus, elles forment un réseau que les lymphocytes T utilisent comme système de guidage. Ce réseau forme des petits canaux (ou conduits) qui permettent le transport rapide, d'antigène soluble ou de cytokines, de la lymphe aux veinules à endothelium épais (HEV). Le phénotype ainsi que les autres fonctions des TRCs demeurent encore à ce jour inconnus. Nous avons trouvé que l'accès des lymphocytes T CD4+ et CD8+ aux ganglions joue un rôle central pour l'homéostasie. Interleukin-7 (IL-7) est un facteur de survie essentiel pour les lymphocytes T naïfs dont la source cellulaire dans la périphérie était mal définie. Nous avons identifié les TRCs dans les ganglions comme source principale d'interleukin-7 (IL-7). In vitro, les TRCs étaient capable de prévenir la mort des lymphocytes T mais pas celle de lymphocytes B grâce à la sécrétion d'IL-7 et de CCL19. En utilisant des souris déficientes du gène CCL19, nous avons observé que l'homéostasie des lymphocytes T dépend aussi de CCL19 in vivo. Les données suggèrent que les TRCs aident à maintenir un répertoire large et diversifié de cellules T et ainsi l'immunocompétence. Pour déterminer si les TRCs pourraient jouer un rote également dans la pathologie, nous avons caractérisé des organes lymphoïdes tertiaires (TLOs) souvent associés avec l'inflammation chronique. Les TLOs ressemblent à des ganglions ou des plaques de Peyer pas seulement en ce qui concerne la présence de lymphocytes. Nous avons constaté que les TLOs forment des réseaux de TRC et un système fonctionnel de conduits. La formation de ces structures est fortement diminuée dans l'absence du signal lymphotoxin ou des cellules connues comme ymphoid tissue-inducer tells: Les TRCs dans les TLOs produisent les chimiokines CCL19, CCL21 et possiblement aussi IL-7 qui sont impliquées dans le développement des TLOs. Les cellules stromales jouent donc un rôle central dans l'initation et la perpétuation des maladies inflamatoires chroniques et pourraient être une cible intéressante pour la thérapie.

The frequency and prognostic impact of dic(9;20)(p13.2;q11.2) in childhood B-cell precursor acute lymphoblastic leukemia: results from the NOPHO ALL-2000 trial.

The dic(9;20)(p13.2;q11.2) is reported to be present in ∼2% of childhood B-cell precursor acute lymphoblastic leukemia (BCP ALL). However, it easily escapes detection by G-banding analysis and its true prevalence is hence unknown. We performed interphase fluorescence in situ hybridization analyses-in a three-step manner-using probes for: (i) CDKN2A at 9p21, (ii) 20p and 20q subtelomeres and (iii) cen9 and cen20. Out of 1033 BCP ALLs diagnosed from 2001 to 2006, 533 were analyzed; 16% (84/533) displayed 9p21 deletions, of which 30% (25/84) had dic(9;20). Thus, dic(9;20)-positivity was found in 4.7% (25/533), making it the third most common genetic subgroup after high hyperdiploidy and t(12;21)(p13;q22). The dic(9;20) was associated with a female predominance and an age peak at 3 years; 18/25 (72%) were allocated to non-standard risk treatment at diagnosis. Including cases detected by G-banding alone, 29 dic(9;20)-positive cases were treated according to the NOPHO ALL 2000 protocol. Relapses occurred in 24% (7/29) resulting in a 5-year event-free survival of 0.69, which was significantly worse than for t(12;21) (0.87; P=0.002) and high hyperdiploidy (0.82; P=0.04). We conclude that dic(9;20) is twice as common as previously surmised, with many cases going undetected by G-banding analysis, and that dic(9;20) should be considered a non-standard risk abnormality.

The Th2 lymphoproliferation developing in LatY136F mutant mice triggers polyclonal B cell activation and systemic autoimmunity.

Lat(Y136F) knock-in mice harbor a point mutation in Tyr(136) of the linker for activation of T cells and show accumulation of Th2 effector cells and IgG1 and IgE hypergammaglobulinemia. B cell activation is not a direct effect of the mutation on B cells since in the absence of T cells, mutant B cells do not show an activated phenotype. After adoptive transfer of linker for activation of T cell mutant T cells into wild-type, T cell-deficient recipients, recipient B cells become activated. We show in vivo and in vitro that the Lat(Y136F) mutation promotes T cell-dependent B cell activation leading to germinal center, memory, and plasma cell formation even in an MHC class II-independent manner. All the plasma and memory B cell populations found in physiological T cell-dependent B cell responses are found. Characterization of the abundant plasmablasts found in secondary lymphoid organs of Lat(Y136F) mice revealed the presence of a previously uncharacterized CD93-expressing subpopulation, whose presence was confirmed in wild-type mice after immunization. In Lat(Y136F) mice, B cell activation was polyclonal and not Ag-driven because the increase in serum IgG1 and IgE concentrations involved Abs and autoantibodies with different specificities equally. Although the noncomplement-fixing IgG1 and IgE are the only isotypes significantly increased in Lat(Y136F) serum, we observed early-onset systemic autoimmunity with nephritis showing IgE autoantibody deposits and severe proteinuria. These results show that Th2 cells developing in Lat(Y136F) mice can trigger polyclonal B cell activation and thereby lead to systemic autoimmune disease.

T and B lymphocytes exert distinct effects on the homeostasis of NK cells.

There is growing evidence that lymphocytes impact the development and/or function of other lymphocyte populations. Based on such observations we have tested whether the NK cell compartment was phenotypically and functionally altered in the absence of B and/or T cells. Here we show that T cell deficiency significantly accelerates BM NK cell production and the subsequent seeding of splenic and liver NK cell compartments. In contrast, B cell deficiency reduces splenic NK cell survival. In the absence of T and B cells, the size of the NK cell compartments is determined by the combination of these positive and negative effects. Even though NK cell homeostasis is significantly altered, NK cells from T and/or B cell-deficient mice show a normal capacity to kill a susceptible target cell line and to produce IFN. Nevertheless, we noted that the usage of MHC class I-specific Ly49 family receptors was significantly altered in the absence of T and/or B cells. In general, B cell deficiency expanded Ly49 receptor usage, while T cell deficiency exerted both positive and negative effects. These findings show that B and T cells significantly and differentially influence the homeostasis and the phenotype of NK cells.

IgG subclass switch capacity is low in switched and in IgM-only, but high in IgD+IgM+, post-germinal center (CD27+) human B cells.

Recent studies have shown that in humans the germinal center reactions produce three types of V(D)J mutated B cells in similar proportions, i.e. Ig-switched, IgD-IgM+ (IgM-only) and IgD+IgM+ cells, and that together they form the CD27+ compartment of recirculating B cells. We investigated the Ig isotype switch capacity of these cells. Peripheral blood B subsets were sorted and IgG subclass secretion in presence or absence of IL-4 was compared in B cell assays which lead to Ig secretion in all (coculture with EL-4 thymoma cells) or only in CD27+ (CD40L stimulation) B cells. Already switched IgG+ B cells showed no significant sequential switch and IgM-only cells also had a low switch capacity, but IgD+CD27+ switched as much as IgD+CD27- B cells to all IgG subclasses. Thus, in switched B cells some alterations compromising further switch options occur frequently; IgM-only cells may result from aborted switch. However, IgD+CD27+ human B cells, extensively V(D)J mutated and "naive" regarding switch, build up a repertoire of B cells combining (1) novel cross-reactive specificities, (2) increased differentiation capacity (including after T-independent stimulation by Staphylococcus aureus Cowan I) and (3) the capacity to produce appropriate isotypes when they respond to novel pathogens.

Non-classical karyotypic features in relapsed childhood B-cell precursor acute lymphoblastic leukemia.

Karyotype analysis of acute lymphoblastic leukemia (ALL) at diagnosis has provided valuable prognostic markers for treatment stratification. However, reports of cytogenetic studies of relapsed ALL samples are limited. We compared the karyotypes from 436 nonselected B-cell precursor ALL patients at initial diagnosis and of 76 patients at first relapse. We noticed a relative increase of karyotypes that did not fall into the classic ALL cytogenetic subgroups (high hyperdiploidy, t(12;21), t(9;22), 11q23, t(1;19), <45 chromosomes) in a group of 29 patients at relapse (38%) compared to 130 patients at presentation (30%). Non-classical cytogenetic aberrations in these 29 patients were mostly found on chromosomes 1, 2, 7, 9, 13, 14, and 17. We also describe six rare reciprocal translocations, three of which involved 14q32. The most frequent abnormalities were found in 9p (12/29 cases) and were associated with a marked decrease in the duration of the second remission, but not of the probability of 10-year event-free survival after relapse treatment. From 29 patients with non-classical cytogenetic aberrations, only 8 (28%) had been stratified to a high risk-arm on the first treatment protocol, suggesting that this subgroup might benefit from the identification of new prognostic markers in future studies.

Infection of B cells with hepatitis C virus for the development of lymphoproliferative disorders in patients with chronic hepatitis C.

Infection with hepatitis C virus (HCV) is associated with lymphoproliferative disorders, represented by essential mixed cryoglobulinemia and B-cell non-Hodgkin's lymphoma, but the pathogenic mechanism remains obscure. HCV may infect B cells or interact with their cell surface receptors, and induce lymphoproliferation. The influence of HCV infection of B cells on the development of lymphoproliferative disorders was evaluated in 75 patients with persistent HCV infection. HCV infection was more prevalent (63% vs. 16%, 14%, or 17% P < 0.05 for each), and HCV RNA levels were higher (3.35 +/- 3.85 vs. 1.75 +/- 2.52, 2.15 +/- 2.94 or 2.10 +/- 2.90 log copies/100 ng, P < 0.01 for each) in B cells than CD4(+), CD8(+) T cells or other cells. Negative-strand HCV RNA, as a marker of viral replication, was detected in B cells from four of the 75 (5%) patients. Markers for lymphoproliferative disorders were more frequent in the 50 patients with chronic hepatitis C than the 32 with chronic hepatitis B, including cryoglobulinemia (26% vs. 0%, P < 0.001), low CH(50) levels (48% vs. 3%, P = 0.012), and the clonality of B cells (12% vs. 0%, P < 0.01). By multivariate analysis, HCV RNA in B cells was an independent factor associated with the presence of at least one marker for lymphoproliferation (odds ratio: 1.98 [95% confidence interval: 1.36-7.24], P = 0.027). Based on the results obtained, the infection of B cells with HCV would play an important role in the development of lymphoproliferative disorders.

Th2 activities induced during virgin T cell priming in the absence of IL-4, IL-13, and B cells.

Virgin T cells being primed to Th2-inducing or Th1-inducing Ags, respectively, start to synthesize IL-4 or IFN-gamma as they begin to proliferate. Parallel respective induction of B cells to produce gamma1 or gamma2a switch transcripts provides additional evidence of early divergent Th activity. This report concerns the roles of IL-4, IL-13, and B cells in these early events in vivo. Th2 responses were induced in lymph nodes against hapten-protein given s.c. with killed Bordetella pertussis adjuvant. In T cell proliferation in wild-type mice, IL-4 message up-regulation and gamma1 and epsilon switch transcript production were underway 48-72 h after immunization. The absence of IL-4, IL-13, or B cells did not alter the early T cell proliferative response. The gamma1 and epsilon switch transcript production was still induced in the absence of IL-4, IL-13, or both, but at a reduced level, while the dominance of switching to IgG1 in the extrafollicular hapten-specific plasma cell response was retained. The up-regulation of IL-4 message was not reduced or delayed in the absence of B cells and was only marginally reduced by the absence of IL-13. It is concluded that signals delivered by dendritic cells, which are not dependent on the presence of IL-4, IL-13, or B cells, can prime virgin T cells and induce the early Th2 activities studied. These early events that direct virgin T cells toward Th2 differentiation contrast with the critical later role of Th2 cytokines in selectively expanding Th2 clones and driving further IL-4 synthesis.