Tom A. Barr

B cell depletion therapy ameliorates autoimmune disease through ablation of IL-6–producing B cells

IL-6–producing B cells contribute to EAE pathology and possibly human MS, whereas ablation of B cell IL-6 is associated with a reduced Th17 response.

CD11c depletion severely disrupts Th2 induction and development in vivo.

Although dendritic cells (DCs) are adept initiators of CD4+ T cell responses, their fundamental importance in this regard in Th2 settings remains to be demonstrated. We have used CD11c–diphtheria toxin (DTx) receptor mice to deplete CD11c+ cells during the priming stage of the CD4+ Th2 response against the parasitic helminth Schistosoma mansoni. DTx treatment significantly depleted CD11c+ DCs from all tissues tested, with 70–80% efficacy. Even this incomplete depletion resulted in dramatically impaired CD4+ T cell production of Th2 cytokines, altering the balance of the immune response and causing a shift toward IFN-γ production. In contrast, basophil depletion using Mar-1 antibody had no measurable effect on Th2 induction in this system. These data underline the vital role that CD11c+ antigen-presenting cells can play in orchestrating Th2 development against helminth infection in vivo, a response that is ordinarily balanced so as to prevent the potentially damaging production of inflammatory cytokines.

TLR-mediated stimulation of APC: Distinct cytokine responses of B cells and dendritic cells.

In addition to their role in humoral immunity, B lymphocytes are important antigen‐presenting cells (APC). In the same way as other APC, B cells make cytokines upon activation and have the potential to modulate T cell responses. In this study, we investigated which mouse B cell subsets are the most potent cytokine producers, and examined the role of Toll‐like receptors (TLR) in the control of secretion of IL‐6, IL‐10, IL‐12 and IFN‐γ by B cells. Production of some cytokines was restricted to particular subsets. Marginal zone and B1 cells were the predominant source of B cell IL‐10 in the spleen. Conversely, follicular B cells were found to express IFN‐γ mRNA directly ex vivo. The nature of the activating stimulus dramatically influenced the cytokine made by B cells. Thus, in response to combined TLR stimulation, or via phorbol esters, IFN‐γ was secreted. IL‐10 was elicited by T‐dependent activation or stimulation through TLR2, 4 or 9. This pattern of cytokine expression contrasts with that elicited from dendritic cells. QRT‐PCR array data indicate that this may be due to differential expression of TLR signalling molecules, effectors and adaptors. Our data highlight the potentially unique nature of immune modulation when B cells act as APC.

Helminth-induced CD19+CD23hi B cells modulate experimental allergic and autoimmune inflammation

Numerous population studies and experimental models suggest that helminth infections can ameliorate immuno‐inflammatory disorders such as asthma and autoimmunity. Immunosuppressive cell populations associated with helminth infections include Treg and alternatively‐activated macrophages. In previous studies, we showed that both CD4+CD25+ Treg, and CD4– MLN cells from Heligmosomoides polygyus‐infected C57BL/6 mice were able to transfer protection against allergic airway inflammation to sensitized but uninfected animals. We now show that CD4–CD19+ MLN B cells from infected, but not naïve, mice are able to transfer a down‐modulatory effect on allergy, significantly suppressing airway eosinophilia, IL‐5 secretion and pathology following allergen challenge. We further demonstrate that the same cell population can alleviate autoimmune‐mediated inflammatory events in the CNS, when transferred to uninfected mice undergoing myelin oligodendrocyte glycoprotein(p35–55)‐induced EAE. In both allergic and autoimmune models, reduction of disease was achieved with B cells from helminth‐infected IL‐10−/− donors, indicating that donor cell‐derived IL‐10 is not required. Phenotypically, MLN B cells from helminth‐infected mice expressed uniformly high levels of CD23, with follicular (B2) cell surface markers. These data expand previous observations and highlight the broad regulatory environment that develops during helminth infections that can abate diverse inflammatory disorders in vivo.

Schistosomes Induce Regulatory Features in Human and Mouse CD1d(hi) B Cells: Inhibition of Allergic Inflammation by IL-10 and Regulatory T Cells

Chronic helminth infections, such as schistosomes, are negatively associated with allergic disorders. Here, using B cell IL-10-deficient mice, Schistosoma mansoni-mediated protection against experimental ovalbumin-induced allergic airway inflammation (AAI) was shown to be specifically dependent on IL-10-producing B cells. To study the organs involved, we transferred B cells from lungs, mesenteric lymph nodes or spleen of OVA-infected mice to recipient OVA-sensitized mice, and showed that both lung and splenic B cells reduced AAI, but only splenic B cells in an IL-10-dependent manner. Although splenic B cell protection was accompanied by elevated levels of pulmonary FoxP3+ regulatory T cells, in vivo ablation of FoxP3+ T cells only moderately restored AAI, indicating an important role for the direct suppressory effect of regulatory B cells. Splenic marginal zone CD1d+ B cells proved to be the responsible splenic B cell subset as they produced high levels of IL-10 and induced FoxP3+ T cells in vitro. Indeed, transfer of CD1d+ MZ-depleted splenic B cells from infected mice restored AAI. Markedly, we found a similarly elevated population of CD1dhi B cells in peripheral blood of Schistosoma haematobium-infected Gabonese children compared to uninfected children and these cells produced elevated levels of IL-10. Importantly, the number of IL-10-producing CD1dhi B cells was reduced after anti-schistosome treatment. This study points out that in both mice and men schistosomes have the capacity to drive the development of IL-10-producing regulatory CD1dhi B cells and furthermore, these are instrumental in reducing experimental allergic inflammation in mice.

B Cell Intrinsic MyD88 Signals Drive IFN-γ Production from T Cells and Control Switching to IgG2c

The question of whether Ab responses to T-dependent Ags require B cell intrinsic signaling via the main TLR adaptor (MyD88) has become embroiled in confusion. In part this may be related to the methods used to analyze B cell intrinsic signaling. We have used a mixed bone marrow chimera model to generate mice in which the B cell compartment is completely deficient in MyD88 expression, while the other hematopoietic lineages are largely normal. These mice were immunized with T-dependent Ags or infected with Salmonella. We found that the Ag-specific IgG2c primary response was absolutely dependent on MyD88 signaling to B cells, while other Ig classes were not (IgG1 and IgG3) or much less so (IgG2b, IgA). The MyD88B−/− chimeric mice exhibited an impairment of development of IFN-γ effector T cells, a likely contributory factor in the lack of IgG2c. We also found that B cell intrinsic MyD88 signals are required for the production of natural Abs. The data emphasize the nonredundant role of B cells as programmers of T cell differentiation in vivo.

Dying and necrotic neutrophils are anti-inflammatory secondary to the release of α-defensins

Neutrophils are recruited to sites of injury but their timely removal is thought to be vital to prevent exacerbating inflammation. In addition, the recognition of apoptotic cells by cells of the innate immune system provides potent anti-inflammatory and anti-immunogenic signals. In this article, we describe how human neutrophils dying by apoptosis or necrosis release anti-inflammatory peptides, the α-defensins. This family of small cationic peptides effectively inhibits the secretion of multiple proinflammatory cytokines and NO from macrophages, the main innate immune cell found at sites of chronic inflammation. In addition, the systemic administration of necrotic neutrophil supernatants and α-defensins protects mice from a murine model of peritonitis. Hence. their effects may be far-reaching and serve to kill microbes while regulating a potentially tissue-destructive inflammatory response.

A potent adjuvant effect of CD40 antibody attached to antigen

There is great potential for novel vaccines based on recombinant proteins and synthetic peptides. Unfortunately these antigens often lack the immunogenicity of whole, killed pathogens used in traditional vaccines. Thus there is strong interest in the identification of immunological adjuvants with low reactogenicity, but high potency, to enhance immune responses and realize the potential of these new vaccine strategies. CD40 antibodies have been shown to have adjuvant effects when administered at very high doses. These large doses are impractical and induce a cascade of cytokine release giving rise to septic shock‐like symptoms, as well as splenomegaly and polyclonal antibody production. We show here that a very small amount of CD40 antibody can exhibit potent adjuvant effects when attached to soluble antigen. The lack of detectable systemic effects indicates that this method may be a powerful and practical means of enhancing the efficacy of recombinant vaccines.

Toll-like receptor 4 signalling through MyD88 is essential to control Salmonella enterica serovar Typhimurium infection, but not for the initiation of bacterial clearance

Toll‐like receptor‐4 (TLR4) is important in protection against lethal Salmonella enterica serovar Typhimurium (S. Typhimurium) infection. Control of the early stages of sublethal S. Typhimurium infection in mice depends on TLR4‐dependent activation of macrophages and natural killer (NK) cells to drive an inflammatory response. TLR4 signals through the adapter proteins Mal/MyD88 and TRIF‐related adaptor molecule (TRAM)/TIR‐domain‐containing adaptor‐inducing interferon‐b (TRIF). In the mouse typhoid model we showed that TLR4 and MyD88, but not Mal or TRIF, are essential for the control of exponential S. Typhimurium growth. TRIF−/− mice have a higher bacterial load in comparison with wild‐type mice during a sublethal infection because TRIF is important for bacterial killing during the first day of systemic disease. Minimal pro‐inflammatory responses were induced by S. Typhimurium infection of macrophages from TLR4−/−, MyD88−/− and TRIF−/− mice in vitro. Pro‐inflammatory responses from Mal−/− macrophages were similar to those from wild‐type cells. The pro‐inflammatory responses of TRIF−/− macrophages were partially restored by the addition of interferon‐γ (IFN‐γ), and TRIF−/− mice produced markedly enhanced IFN‐γ levels, in comparison to wild‐type mice, probably explaining why bacterial growth can be controlled in these mice. TLR4−/−, MyD88−/−, TRIF−/− and Mal−/− mice all initiated clearance of S. Typhimurium, suggesting that TLR4 signalling is not important in driving bacterial clearance in comparison to its critical role in controlling early bacterial growth in mouse typhoid.

Cutting Edge: IL-6–Dependent Autoimmune Disease: Dendritic Cells as a Sufficient, but Transient, Source

Mice lacking IL-6 are resistant to autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE), which is driven by CNS-reactive CD4+ T cells. There are multiple cellular sources of IL-6, but the critical source in EAE has been uncertain. Using cell-specific IL-6 deficiency in models of EAE induced by active immunization, passive transfer, T cell transfer, and dendritic cell transfer, we show that neither the pathogenic T cells nor CNS-resident cells are required to produce IL-6. Instead, the requirement for IL-6 was restricted to the early stages of T cell activation and was entirely controlled by dendritic cell–derived IL-6. This reflected the loss of IL-6R expression by T cells over time. These data explain why blockade of IL-6R only achieves protection against EAE if used at the time of T cell priming. The implications for therapeutic manipulation of IL-6 signaling in human T cell–driven autoimmune conditions are considered.