Toll-like receptors control the accumulation of neutrophils in lymph nodes that expand CD4+ T cells during experimental autoimmune encephalomyelitis

Toll-like receptors (TLR) control the activation of dendritic cells that prime CD4⁺ T cells in draining lymph nodes, where these T cells then undergo massive clonal expansion. The mechanisms controlling this clonal T cell expansion are poorly defined. Using the CD4⁺ T cell-mediated disease experimental autoimmune encephalomyelitis (EAE), we show here that this process is markedly suppressed when TLR9 signaling is increased, without noticeably affecting the transcriptome of primed T cells, indicating a purely quantitative effect on CD4⁺ T cell expansion. Addressing the underpinning mechanisms revealed that CD4⁺ T cell expansion was preceded and depended on the accumulation of neutrophils in lymph nodes a few days after immunization. Underlying the importance of this immune regulation pathway, blocking neutrophil accumulation in lymph nodes by treating mice with a TLR9 agonist inhibited EAE progression in mice with defects in regulatory T cells or regulatory B cells, which otherwise developed a severe chronic disease. Collectively, this study demonstrates the key role of neutrophils in the quantitative regulation of antigen-specific CD4⁺ T cell expansion in lymph nodes, and the counter-regulatory role of TLR signaling in this process.

Proinflammatory GM-CSF-producing B cells in multiple sclerosis and B cell depletion therapy

B cells are not limited to producing protective antibodies; they also perform additional functions relevant to both health and disease. However, the relative contribution of functionally distinct B cell subsets in human disease, the signals that regulate the balance between such subsets, and which of these subsets underlie the benefits of B cell depletion therapy (BCDT) are only partially elucidated. We describe a proinflammatory, granulocyte macrophage-colony stimulating factor (GM-CSF)-expressing human memory B cell subset that is increased in frequency and more readily induced in multiple sclerosis (MS) patients compared to healthy controls. In vitro, GM-CSF-expressing B cells efficiently activated myeloid cells in a GM-CSF-dependent manner, and in vivo, BCDT resulted in a GM-CSF-dependent decrease in proinflammatory myeloid responses of MS patients. A signal transducer and activator of transcription 5 (STAT5)- and STAT6-dependent mechanism was required for B cell GM-CSF production and reciprocally regulated the generation of regulatory IL-10-expressing B cells. STAT5/6 signaling was enhanced in B cells of untreated MS patients compared with healthy controls, and B cells reemerging in patients after BCDT normalized their STAT5/6 signaling as well as their GM-CSF/IL-10 cytokine secretion ratios. The diminished proinflammatory myeloid cell responses observed after BCDT persisted even as new B cells reconstituted. These data implicate a proinflammatory B cell/myeloid cell axis in disease and underscore the rationale for selective targeting of distinct B cell populations in MS and other human autoimmune diseases.

B-type suppression: a role played by "regulatory B cells" or "regulatory plasma cells"?

B-cell depletion can improve disease in some patients with rheumatoid arthritis or multiple sclerosis, indicating the pathogenic contribution of B cells to autoimmunity. However, studies in mice have demonstrated that B cells have immunosuppressive functions as well, with IL-10 being a critical mediator of B-cell-mediated suppression. IL-10-secreting B cells have been shown to promote disease remission in some mouse models of autoimmune disorders. Human B cells also produce IL-10, and evidence is accumulating that human IL-10-producing B cells might inhibit immunity. There is considerable interest in identifying the phenotype of B cells providing IL-10 in a suppressive manner, which would facilitate the analysis of the molecular mechanisms controlling this B-cell property. Here, we review current knowledge on the B-cell subpopulations found to provide suppressive functions in mice, considering both the pathological context in which they were identified and the signals that control their induction. We discuss the phenotype of B cells that have IL-10-dependent regulatory activities in mice, which leads us to propose that antibody-secreting cells are, in some cases at least, the major source of B-cell-derived regulatory IL-10 in vivo. Anti-inflammatory cytokine production by antibody-secreting cells offers a novel mechanism for the coordination of innate and humoral immune responses.

A method for the generation of TCR retrogenic mice

Retrogenic mice provide a unique system for rapidly analyzing the function of genes in the hematopoietic system. Here, we provide a detailed protocol for the production of retrogenic mice expressing genes coding for T cell receptor (TCR) for antigen. This technology should be easy to establish in any laboratory and should allow for a rapid progress in our understanding of the functional roles of TCR repertoires in immunity.

Interleukin-10-producing B cells and the regulation of immunity

B cells are usually considered primarily for their unique capacity to produce antibodies after differentiation into plasma cells. In addition to their roles as antibody-producing cells, it has become apparent during the last 10 years that B cells also perform important functions in immunity through the production of cytokines. In particular, it was shown that B cells could negatively regulate immunity through provision of interleukin (IL)-10 during autoimmune and infectious diseases in mice. Here, we review data on the suppressive functions of B cells in mice with particular emphasis on the signals controlling the acquisition of such suppressive functions by B cells, the phenotype of the B cells involved in the negative regulation of immunity, and the processes targeted by this inhibitory circuit. Finally, we discuss the possibility that human B cells might also perform similar inhibitory functions through the provision of IL-10, and review data suggesting that such B cell-mediated regulatory activities might be impaired in patients with autoimmune diseases.

Intrinsic Toll-like receptor signalling drives regulatory function in B cells

B cells can contribute to immunity through production of antibodies, presentation of antigen to T cells, and secretion of cytokines. B cell activation can result in various outcomes for the host. In general B cell responses are beneficial during infections, and deleterious during autoimmune diseases. However, B cells can also limit host defence against pathogens, and protect from autoimmune pathologies. B cells can therefore act both as drivers and as regulators of immunity. Understanding how these opposite functions are mediated shall stimulate the elaboration of novel approaches for manipulating the immune system. B cells might acquire distinct functional properties depending on their mode of activation. Antigen-specific B cell responses require triggering of B cell receptor (BCR) by antigen, and provision of helper signals by T cells. B cells also express various innate immune receptors, and can directly respond to microbial products. Here, we discuss how intrinsic signalling via Toll-like receptors contributes to the suppressive functions of B cells during autoimmune and infectious diseases.

Functional interactions between B lymphocytes and the innate immune system

The immune system is composed of multiple cell types, which together improve the resistance of the organism against infections. The unfolding of a successful host response ensuring effective protection against pathogens requires an appropriate coordination of the different players of the immune system. Innate cells and T cells extensively communicate during immune reactions, providing multiple opportunities for the mutual coordination of these two defense pathways. Little is known about the functional interactions between B and innate cells, and it is generally assumed that they influence each other indirectly through effects on T cells. However, recent studies highlighted important roles for innate cells in initial presentation of antigen to B cells after immunization, and in long-term maintenance of antibody-producing cells in bone marrow after resolution of immune responses. Furthermore, it was found that activated B cells could regulate the activity of innate cells through production of cytokines. Here, we review how direct interactions between innate and B cells can contribute to orchestration of humoral and cellular immunity.

Activation of CD4⁺ Foxp3⁺ regulatory T cells proceeds normally in the absence of B cells during EAE

B cells and regulatory T (Treg) cells can both facilitate remission from experimental auto immune encephalomyelitis (EAE), a disease of the central nervous system (CNS) used as a model for multiple sclerosis (MS). Considering that B-cell-depletion therapy (BCDT) is used to treat MS patients, we asked whether Treg-cell activation depended on B cells during EAE. Treg-cell proliferation, accumulation in CNS, and augmentation of suppressive activity in the CNS were normal in B-cell-deficient mice, indicating that B cells are not essential for activation of the protective Treg-cell response and thus provide an independent layer of regulation. This function of B cells involved early suppression of the encephalitogenic CD4(+) T-cell response, which was enhanced in B-cell-deficient mice. CD4(+) T-cell depletion was sufficient to intercept the transition from acute-to-chronic EAE when applied to B-cell-deficient animals that just reached the peak of disease severity. Intriguingly, this treatment did not improve disease when applied later, implying that chronic disability was ultimately maintained independently of pathogenic CD4(+) T cells. Collectively, our data indicate that BCDT is unlikely to impair Treg-cell function, yet it might produce undesirable effects on T-cell-mediated autoimmune pathogenesis.

Characterization of AKT independent effects of the synthetic AKT inhibitors SH-5 and SH-6 using an integrated approach combining transcriptomic profiling and signaling pathway perturbations

Background

Signal transduction processes mediated by phosphatidyl inositol phosphates affect a broad range of cellular processes such as cell cycle progression, migration and cell survival. The protein kinase AKT is one of the major effectors in this signaling network. Chronic AKT activation contributes to oncogenic transformation and tumor development. Therefore, analogs of phosphatidyl inositol phosphates (PIAs) were designed as new small drugs to block AKT activity for cancer treatment. Here we characterize the biological effects of the PIAs SH-5 and SH-6 in colorectal cancer cell lines.

Methods

Serum-starved or serum-supplemented human colorectal cancer cell lines SW480, HT29 and HCT116 were exposed to SH-5 and SH-6. AKT activation was determined by western blotting. Cell viability was assessed using a colorimetric XTT-based assay, apoptosis and cell cycle changes were monitored by FACS analysis. The dynamics of cell morphology alterations was evaluated by confocal and time-lapse microscopy. Transcriptional changes due to inhibitor treatment were analyzed using Affymetrix HG-U133A microarrays and RT-PCR.

Results

While the PIAs clearly reduce AKT phosphorylation in serum starved cells, we did not observe a significant reduction under serum supplemented conditions, giving us the opportunity to analyze AKT independent effects of these compounds. Both inhibitors induce broadly the same morphological alterations, in particular changes in cell shape and formation of intracellular vesicles. Moreover, we observed the induction of binucleated cells specifically in the SW480 cell line. Gene expression analysis revealed transcriptional alterations, which are mostly cell line specific. In accordance to the phenotype we found a gene group associated with mitosis and spindle organization down regulated in SW480 cells, but not in the other cell lines. A bioinformatics analysis using the Connectivity Map linked the gene expression pattern of the inhibitor treated SW480 cells to PKC signaling. Using confocal laser scanning microscopy and time lapse recording we identified a specific defect in the last step of the cytokinesis as responsible for the binucleation.

Conclusions

The PIAs SH-5 and SH-6 impinge on additional cellular targets apart from AKT in colorectal cancer cells. The effects are mostly cell line specific and have an influence at the outcome of the treatment. In view of potential clinical trials it will be necessary to take these diverse effects into consideration to optimize patient treatment.