Mohini Gray

Apoptotic cells protect mice from autoimmune inflammation by the induction of regulatory B cells

The maintenance of immune tolerance to apoptotic cells (AC) within an inflammatory milieu is vital to prevent autoimmunity. To investigate this, we administered syngeneic AC i.v. into mice carrying a cohort of ovalbumin (OVA)-specific transgenic T cells (DO11.10) along with OVA peptide and complete Freunds adjuvant, observing a dramatic increase in OVA-specific IL-10 secretion. Activated splenic B cells responded directly to AC, increasing secretion of IL-10, and this programming by AC was key to inducing T cell-derived IL-10. We went on to ask whether AC are able to modulate the course of autoimmune-mediated, chronic inflammation. AC given up to 1 month before the clinical onset of collagen-induced arthritis protected mice from severe joint inflammation and bone destruction. Antigen-specific CD4+ T cells again secreted significantly more IL-10, associated with a reduced titer of pathogenic anti-collagen II antibodies. Inhibition of IL-10 in vivo reversed the beneficial effects of AC. Passive transfer of B cells from AC-treated mice provided significant protection from arthritis. These data demonstrate that AC exert a profound influence on an adaptive immune response through the generation of CD19+ regulatory B cells, which in turn are able to influence the cytokine profile of antigen-specific effector T cells.

Anti-Inflammatory Role of the Murine Formyl-Peptide Receptor 2: Ligand-Specific Effects on Leukocyte Responses and Experimental Inflammation

The human formyl-peptide receptor (FPR)-2 is a G protein-coupled receptor that transduces signals from lipoxin A4, annexin A1, and serum amyloid A (SAA) to regulate inflammation. In this study, we report the creation of a novel mouse colony in which the murine FprL1 FPR2 homologue, Fpr2, has been deleted and describe its use to explore the biology of this receptor. Deletion of murine fpr2 was verified by Southern blot analysis and PCR, and the functional absence of the G protein-coupled receptor was confirmed by radioligand binding assays. In vitro, Fpr2−/− macrophages had a diminished response to formyl-Met-Leu-Phe itself and did not respond to SAA-induced chemotaxis. ERK phosphorylation triggered by SAA was unchanged, but that induced by the annexin A1-derived peptide Ac2–26 or other Fpr2 ligands, such as W-peptide and compound 43, was attenuated markedly. In vivo, the antimigratory properties of compound 43, lipoxin A4, annexin A1, and dexamethasone were reduced notably in Fpr2−/− mice compared with those in wild-type littermates. In contrast, SAA stimulated neutrophil recruitment, but the promigratory effect was lost following Fpr2 deletion. Inflammation was more marked in Fpr2−/− mice, with a pronounced increase in cell adherence and emigration in the mesenteric microcirculation after an ischemia–reperfusion insult and an augmented acute response to carrageenan-induced paw edema, compared with that in wild-type controls. Finally, Fpr2−/− mice exhibited higher sensitivity to arthrogenic serum and were completely unable to resolve this chronic pathology. We conclude that Fpr2 is an anti-inflammatory receptor that serves varied regulatory functions during the host defense response. These data support the development of Fpr2 agonists as novel anti-inflammatory therapeutics.

Human beta-defensin 3 has immunosuppressive activity in vitro and in vivo.

β‐defensins are antimicrobial peptides with an essential role in the innate immune response. In addition β‐defensins can also chemoattract cells involved in adaptive immunity. Until now, based on evidence from dendritic cell stimulation, human β defensin‐3 (hBD3) was considered pro‐inflammatory. We present evidence here that hBD3 lacks pro‐inflammatory activity in human and mouse primary Mϕ. In addition, in the presence of LPS, hBD3 and the murine orthologue Defb14 (but not hBD2), effectively inhibit TNF‐α and IL‐6 accumulation implying an anti‐inflammatory function. hBD3 also inhibits CD40/IFN‐γ stimulation of Mϕ and in vivo, hBD3 significantly reduces the LPS‐induced TNF‐α level in serum. Recent work has revealed that hBD3 binds melanocortin receptors but we provide evidence that these are not involved in hBD3 immunomodulatory activity. This implies a dual role for hBD3 in antimicrobial activity and resolution of inflammation.

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 tolerogenic role for Toll-like receptor 9 is revealed by B-cell interaction with DNA complexes expressed on apoptotic cells.

Intracellular protein complexes containing nucleic acids are common targets of autoantibodies in many autoimmune diseases. Central tolerance to these antigens is incomplete, yet nucleosomal DNA is expressed on the surface of cells dying by apoptosis. It is commonly believed that autoimmunity is prevented by the rapid uptake of apoptotic cells (ACs) by neighbors or professional phagocytes to which they deliver anti-inflammatory signals. Self-reactive, innate-like B cells contact and are selected by intracellular antigens expressed on ACs; however, how self-tolerance is maintained is not well understood. Here we report that IL-10 production by B cells, stimulated by contact with ACs, results from the engagement of Toll-like receptor 9 (TLR9) within the B cell after recognition of DNA-containing complexes on the surface of ACs. Until now, TLR9 ligation has been considered an inflammatory signal, but we have confirmed a hitherto unexpected immunoregulatory role by demonstrating the absence of the protective effect of ACs during experimental autoimmune encephalitis (EAE) in TLR9-deficient mice. Human circulating CD27+ B cells also respond to DNA-bearing ACs, but not to DNase-treated cells, by secreting IL-10. Chronic autoimmune disease may arise if this tolerance mechanism is not reimposed after episodes of inflammation, or if the regulatory B-cell response is subverted.

The role and regulation of 11β-hydroxysteroid dehydrogenase type 1 in the inflammatory response

Cortisone, a glucocorticoid hormone, was first used to treat rheumatoid arthritis in humans in the late 1940s, for which Hench, Reichstein and Kendall were awarded a Nobel Prize in 1950 and which led to the discovery of the anti-inflammatory effects of glucocorticoids. To be effective, the intrinsically inert cortisone must be converted to the active glucocorticoid, cortisol, by the intracellular action of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). Whilst orally administered cortisone is rapidly converted to the active hormone, cortisol, by first pass metabolism in the liver, recent work has highlighted an anti-inflammatory role for 11beta-HSD1 within specific tissues, including in leukocytes. Here, we review recent evidence pertaining to the anti-inflammatory role of 11beta-HSD1 and describe how inhibition of 11beta-HSD1, as widely proposed for treatment of metabolic disease, may impact upon inflammation. Finally, the mechanisms that regulate 11beta-HSD1 transcription will be discussed.

Innate responses of B cells

In this review, we describe the non‐antibody‐mediated functions of B cells within the immune system. In addition to antibody production, B cells also present antigen to T cells, programme T cell differentiation and regulate effector T cell responses and much of this is mediated by the cytokines they make. We focus on the potential of B cells to perform these functions simply as a result of activation via ‘innate’ receptors (e.g. Toll‐like receptors) and often independently of BCR ligation. We feel an appreciation of these broad and often antigen‐nonspecific functions is important at a time when there is an increasing use of B cell depletion as a therapy for autoimmune disease.

11β-Hydroxysteroid Dehydrogenase Type 1, But Not Type 2, Deficiency Worsens Acute Inflammation and Experimental Arthritis in Mice

Glucocorticoids profoundly influence immune responses, and synthetic glucocorticoids are widely used clinically for their potent antiinflammatory effects. Endogenous glucocorticoid action is modulated by the two isozymes of 11β-hydroxysteroid dehydrogenase (11β-HSD). In vivo, 11β-HSD1 catalyzes the reduction of inactive cortisone or 11-dehydrocorticosterone into active cortisol or corticosterone, respectively, thereby increasing intracellular glucocorticoid levels. 11β-HSD2 catalyzes the reverse reaction, inactivating intracellular glucocorticoids. Both enzymes have been postulated to modulate inflammatory responses. In the K/BxN serum transfer model of arthritis, 11β-HSD1-deficient mice showed earlier onset and slower resolution of inflammation than wild-type controls, with greater exostoses in periarticular bone and, uniquely, ganglion cysts, consistent with greater inflammation. In contrast, K/BxN serum arthritis was unaffected by 11β-HSD2 deficiency. In a distinct model of inflammation, thioglycollate-induced sterile peritonitis, 11β-HSD1-deficient mice had more inflammatory cells in the peritoneum, but again 11β-HSD2-deficient mice did not differ from controls. Additionally, compared with control mice, 11β-HSD1-deficient mice showed greater numbers of inflammatory cells in pleural lavages in carrageenan-induced pleurisy with lung pathology consistent with slower resolution. These data suggest that 11β-HSD1 limits acute inflammation. In contrast, 11β-HSD2 plays no role in acute inflammatory responses in mice. Regulation of local 11β-HSD1 expression and/or delivery of substrate may afford a novel approach for antiinflammatory therapy.

Local Amplification of Glucocorticoids by 11β‐Hydroxysteroid Dehydrogenase Type 1 and Its Role in the Inflammatory Response

Abstract:  Glucocorticoids are widely used to treat chronic inflammatory conditions including rheumatoid arthritis. They promote mechanisms important for normal resolution of inflammation, notably macrophage phagocytosis of leukocytes undergoing apoptosis. Prereceptor metabolism of glucocorticoids by 11β‐hydroxysteroid dehydrogenase type 1 (11β‐HSD1) amplifies intracellular levels of glucocorticoids by oxoreduction of intrinsically inert cortisone (in humans, 11‐dehydrocorticosterone in mice) into active cortisol (corticosterone in mice) within cells expressing the enzyme. Recently, we have shown in a mouse model of acute inflammation, high expression of 11β‐HSD oxoreductase but not dehydrogenase activity in cells elicited rapidly in the peritoneum by a single thioglycollate injection. 11β‐HSD oxoreductase activity remained high in peritoneal cells until the inflammation resolved. In vitro, the 11β‐HSD1 substrate, 11‐dehydrocorticosterone, increased macrophage phagocytosis of apoptotic neutrophils to the same extent as corticosterone. This effect was dependent upon 11β‐HSD1: these cells solely expressed the type 1 11β‐HSD isozyme (not 11β‐HSD2), and carbenoxolone, an 11β‐HSD inhibitor, prevented the increase in phagocytosis elicited by 11‐dehydrocorticosterone. Macrophages from 11β‐HSD1‐deficient mice failed to respond to 11‐dehydrocorticosterone. In vivo, 11β‐HSD1‐deficient mice showed a delay in acquisition of macrophage phagocytic competence and had an increased number of free apoptotic neutrophils during sterile peritonitis. Importantly, in preliminary experiments, 11β‐HSD1‐deficient mice exhibited delayed resolution of inflammation in experimental arthritis. These findings suggest 11β‐HSD1 may be a component of mechanisms engaged early during the inflammatory response that promote its subsequent resolution.

What are regulatory B cells

B cells are now acknowledged to play multiple roles in the immune response, in addition to making antibodies. Their role in regulating T‐cell responses during inflammation has come into focus recently. Thus, IL‐10 production by B cells has been shown to be important in limiting auto‐reactive and pathogen‐driven immune pathology; however, the exact identity of the regulatory B cells remains elusive; do they belong to a committed subset or can all B cells regulate given the appropriate inducing stimuli? A study in this issue of the European Journal of Immunology provides insight into the IL‐10‐producing B cells in humans, suggesting that many B cells have the capacity to make IL‐10 when optimally stimulated via the BCR and TLR9. Despite producing significant amounts of inflammatory cytokines as well, these B cells suppress T‐cell proliferation. This Commentary places this study in the context of what we think we know about regulatory B cells and more importantly highlights the questions we still need to answer.