Role of p47phox in antigen-presenting cell-mediated regulation of humoral immunity in mice

Beyond the Extra Respiration of Phagocytosis: NADPH Oxidase 2 in Adaptive Immunity and Inflammation

Reactive oxygen species (ROS) derived from the phagocyte NADPH oxidase (NOX2) are essential for host defence and immunoregulation. Their levels must be tightly controlled. ROS are required to prevent infection and are used in signalling to regulate several processes that are essential for normal immunity. A lack of ROS then leads to immunodeficiency and autoinflammation. However, excess ROS are also deleterious, damaging tissues by causing oxidative stress. In this review, we focus on two particular aspects of ROS biology: (i) the emerging understanding that NOX2-derived ROS play a pivotal role in the development and maintenance of adaptive immunity and (ii) the effects of excess ROS in systemic disease and how limiting ROS might represent a therapeutic avenue in limiting excess inflammation.

Altered Humoral Immune Responses and IgG Subtypes in NOX2-Deficient Mice and Patients: A Key Role for NOX2 in Antigen-Presenting Cells

Chronic granulomatous disease (CGD) is a primary immunodeficiency resulting from loss of function mutations in the reactive oxygen species generating phagocyte NADPH oxidase (NOX2). CGD patients are prone to infection, but also have an increased susceptibility to autoimmune diseases. The aim of this study was to investigate the role of NOX2 in the regulation of specific immunity. In both CGD patients and NOX2-deficient mice, we observed an alteration in the basal proportions of IgG subtypes. Upon immunization with curdlan-a dectin 1 agonist-NOX2-deficient mice showed increased production of IgG2c compared to controls, and restimulation of lymph node-derived cells led to increased production of IFNγ, but not IL-5, indicative hallmark of an enhanced Th1 response. T cell activation was increased in NOX2-deficient mice and a similar trend was observed in vitro when T cells were co-cultured with NOX2-deficient bone marrow-derived cells. In contrast, no difference in T cell activation was observed when NOX2-deficient T cells were co-cultured with wild-type BMDC. Following stimulation of NOX2-deficient dendritic cells (DCs), no difference in costimulatory molecules was observed, while there was an increase in the release of Th1-driving cytokines. In summary, both CGD patients and CGD mice have an altered IgG subtype distribution, which is associated with an increased IFNγ production. Thus, NOX2 within DCs appears to be an important regulator at the interface of innate and specific immunity, especially after activation of the dectin 1 pathway, limiting immune activation and the development of autoimmunity.

Voltage-Gated Proton Channels as Novel Drug Targets: From NADPH Oxidase Regulation to Sperm Biology

SIGNIFICANCE

Voltage-gated proton channels are increasingly implicated in cellular proton homeostasis. Proton currents were originally identified in snail neurons less than 40 years ago, and subsequently shown to play an important auxiliary role in the functioning of reactive oxygen species (ROS)-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Molecular identification of voltage-gated proton channels was achieved less than 10 years ago. Interestingly, so far, only one gene coding for voltage-gated proton channels has been identified, namely hydrogen voltage-gated channel 1 (HVCN1), which codes for the HV1 proton channel protein. Over the last years, the first picture of putative physiological functions of HV1 has been emerging.

RECENT ADVANCES

The best-studied role remains charge and pH compensation during the respiratory burst of the phagocyte NADPH oxidase (NOX). Strong evidence for a role of HV1 is also emerging in sperm biology, but the relationship with the sperm NOX5 remains unclear. Probably in many instances, HV1 functions independently of NOX: for example in snail neurons, basophils, osteoclasts, and cancer cells.

CRITICAL ISSUES

Generally, ion channels are good drug targets; however, this feature has so far not been exploited for HV1, and hitherto no inhibitors compatible with clinical use exist. However, there are emerging indications for HV1 inhibitors, ranging from diseases with a strong activation of the phagocyte NOX (e.g., stroke) to infertility, osteoporosis, and cancer.

FUTURE DIRECTIONS

Clinically useful HV1-active drugs should be developed and might become interesting drugs of the future.

Phagocyte NADPH oxidase and specific immunity

The phagocyte NADPH oxidase NOX2 produces reactive oxygen species (ROS) and is a well-known player in host defence. However, there is also increasing evidence for a regulatory role of NOX2 in adaptive immunity. Deficiency in phagocyte NADPH oxidase causes chronic granulomatous disease (CGD) in humans, a condition that can also be studied in CGD mice. Clinical observations in CGD patients suggest a higher susceptibility to autoimmune diseases, in particular lupus, idiopathic thrombocytopenic purpura and rheumatoid arthritis. In mice, a strong correlation exists between a polymorphism in a NOX2 subunit and the development of autoimmune arthritis. NOX2 deficiency in mice also favours lupus development. Both CGD patients and CGD mice exhibit increased levels of immunoglobulins, including autoantibodies. Despite these phenotypes suggesting a role for NOX2 in specific immunity, mechanistic explanations for the typical increase of CGD in autoimmune disease and antibody levels are still preliminary. NOX2-dependent ROS generation is well documented for dendritic cells and B-lymphocytes. It is unclear whether T-lymphocytes produce ROS themselves or whether they are exposed to ROS derived from dendritic cells during the process of antigen presentation. ROS are signalling molecules in virtually any cell type, including T- and B-lymphocytes. However, knowledge about the impact of ROS-dependent signalling on T- and B-lymphocyte phenotype and response is still limited. ROS might contribute to Th1/Th2/Th17 cell fate decisions during T-lymphocyte activation and might enhance immunoglobulin production by B-lymphocytes. In dendritic cells, NOX2-derived ROS might be important for antigen processing and cell activation.

P47phox-/- mice are compromised in expansion and activation of CD8+ T cells and susceptible to Trypanosoma cruzi infection

Macrophage activation of NAD(P)H oxidase (NOX2) and reactive oxygen species (ROS) is suggested to kill Trypanosoma cruzi that causes Chagas disease. However, the role of NOX2 in generation of protective immunity and whether these mechanisms are deregulated in the event of NOX2 deficiency are not known, and examined in this study. Our data showed that C57BL/6 p47(phox-/-) mice (lack NOX2 activity), as compared to wild-type (WT) mice, succumbed within 30 days post-infection (pi) to low doses of T. cruzi and exhibited inability to control tissue parasites. P47(phox-/-) bone-marrow and splenic monocytes were not compromised in maturation, phagocytosis and parasite uptake capacity. The deficiency of NOX2 mediated ROS was compensated by higher level of inducible nitric oxide synthase (iNOS) expression, and nitric oxide and inflammatory cytokine (TNF-α, IFN-γ, IL-1β) release by p47(phox-/-) macrophages as compared to that noted in WT controls infected by T. cruzi. Splenic activation of Th1 CD4(+)T cells and tissue infiltration of immune cells in T. cruzi infected p47(phox-/-) mice were comparable to that noted in infected control mice. However, generation and activation of type 1 CD8(+)T cells was severely compromised in p47(phox-/-) mice. In comparison, WT mice exhibited a robust T. cruzi-specific CD8(+)T cell response with type 1 (IFN-γ(+)TNF-α>IL-4+IL-10), cytolytic effector (CD8(+)CD107a(+)IFN-γ(+)) phenotype. We conclude that NOX2/ROS activity in macrophages signals the development of antigen-specific CD8(+)T cell response. In the event of NOX2 deficiency, a compromised CD8(+)T cell response is generated, leading to increased parasite burden, tissue pathogenesis and mortality in chagasic mice.

An AAVS1-targeted minigene platform for correction of iPSCs from all five types of chronic granulomatous disease

There are five genetic forms of chronic granulomatous disease (CGD), resulting from mutations in any of five subunits of phagocyte oxidase, an enzyme complex in neutrophils, monocytes, and macrophages that produces microbicidal reactive oxygen species. We generated induced pluripotent stem cells (iPSCs) from peripheral blood CD34(+) hematopoietic stem cells of patients with each of five CGD genotypes. We used zinc finger nuclease (ZFN) targeting the AAVS1 safe harbor site together with CGD genotype-specific minigene plasmids with flanking AAVS1 sequence to target correction of iPSC representing each form of CGD. We achieved targeted insertion with constitutive expression of desired oxidase subunit in 70-80% of selected iPSC clones. Neutrophils and macrophages differentiated from corrected CGD iPSCs demonstrated restored oxidase activity and antimicrobial function against CGD bacterial pathogens Staphylococcus aureus and Granulibacter bethesdensis. Using a standard platform that combines iPSC generation from peripheral blood CD34(+) cells and ZFN mediated AAVS1 safe harbor minigene targeting, we demonstrate efficient generation of genetically corrected iPSCs using an identical approach for all five genetic forms of CGD. This safe harbor minigene targeting platform is broadly applicable to a wide range of inherited single gene metabolic disorders.

Deficient production of reactive oxygen species leads to severe chronic DSS-induced colitis in Ncf1/p47phox-mutant mice

BACKGROUND

Colitis is a common clinical complication in chronic granulomatous disease (CGD), a primary immunodeficiency caused by impaired oxidative burst. Existing experimental data from NADPH-oxidase knockout mice propose contradictory roles for the involvement of reactive oxygen species in colitis chronicity and severity. Since genetically controlled mice with a point-mutation in the Ncf1 gene are susceptible to chronic inflammation and autoimmunity, we tested whether they presented increased predisposition to develop chronic colitis.

METHODS

Colitis was induced in Ncf1-mutant and wild-type mice by a 1st 7-days cycle of dextran sulfate sodium (DSS), intercalated by a 7-days resting period followed by a 2nd 7-days DSS-cycle. Cytokines were quantified locally in the colon inflammatory infiltrates and in the serum. Leukocyte infiltration and morphological alterations of the colon mucosa were assessed by immunohistochemistry.

RESULTS

Clinical scores demonstrated a more severe colitis in Ncf1-mutant mice than controls, with no recovery during the resting period and a severe chronic colitis after the 2nd cycle, confirmed by histopathology and presence of infiltrating neutrophils, macrophages, plasmocytes and lymphocytes in the colon. Severe colitis was mediated by increased local expression of cytokines (IL-6, IL-10, TNF-α, IFN-γ and IL-17A) and phosphorylation of Leucine-rich repeat kinase 2 (LRRK2). Serological cytokine titers of those inflammatory cytokines were more elevated in Ncf1-mutant than control mice, and were accompanied by systemic changes in functional subsets of monocytes, CD4+ T and B cells.

CONCLUSION

This suggests that an ineffective oxidative burst leads to severe chronic colitis through local accumulation of peroxynitrites, pro-inflammatory cytokines and lymphocytes and systemic immune deregulation similar to CGD.

B-cell activating factor (BAFF) is elevated in chronic granulomatous disease

Chronic Granulomatous Disease (CGD) is an inherited defect in superoxide production leading to life-threatening infections, granulomas, and, possibly, abnormal immunoglobulin concentrations. We investigated whether factors controlling antibody production, such as B-cell activating factor (BAFF), were altered in CGD. CGD subjects had significantly increased mean (2.3-fold, p < 0.0001) plasma concentrations of BAFF compared to healthy donors. Patients on IFN-γ treatment had significantly higher BAFF concentrations compared with CGD patients not taking IFN-γ (1.6-fold, p < 0.005). Leukocytes from CGD subjects produced normal amounts of BAFF in response to IFN-γ or G-CSF in vitro. Expression of BAFF-R and TACI was significantly reduced on CGD B cells. Elevated BAFF in CGD correlated with CRP (R = 0.44), ESR (R = 0.49), and IgM (R = 0.47) and increased rapidly in healthy subjects following intravenous endotoxin administration. These findings suggest that elevated BAFF in CGD subjects and healthy donors is a consequence of acute and chronic inflammation.

Hydrogen peroxide as an immunological transmitter regulating autoreactive T cells

SIGNIFICANCE

An unexpected finding, revealed by positional cloning of genetic polymorphisms controlling models for rheumatoid arthritis, exposed a new function of Ncf1 and NADPH oxidase (NOX) 2 controlled oxidative burst.

RECENT ADVANCES

A decreased capacity to produce ROS due to a natural polymorphism was found to be the major factor leading to more severe arthritis and increased T cell-dependent autoimmunity.

CRITICAL ISSUES

In the vein of this finding, we here review a possible new role of ROS in regulating inflammatory cell and autoreactive T cell activity. It is postulated that peroxide is an immunologic transmitter secreted by antigen-presenting cells that downregulate the responses by autoreactive T cells.

FUTURE DIRECTIONS

This may operate at different levels of T cell selection and activation: during negative selection in the thymus, priming of T cells in draining lymph nodes, and while interacting with macrophages in peripheral target tissues.

CD4(+) T cell vaccination overcomes defective cross-presentation of fungal antigens in a mouse model of chronic granulomatous disease

Aspergillus fumigatus is a model fungal pathogen and a common cause of infection in individuals with the primary immunodeficiency chronic granulomatous disease (CGD). Although primarily considered a deficiency of innate immunity, CGD is also linked to dysfunctional T cell reactivity. Both CD4(+) and CD8(+) T cells mediate vaccine-induced protection from experimental aspergillosis, but the molecular mechanisms leading to the generation of protective immunity and whether these mechanisms are dysregulated in individuals with CGD have not been determined. Here, we show that activation of either T cell subset in a mouse model of CGD is contingent upon the nature of the fungal vaccine, the involvement of distinct innate receptor signaling pathways, and the mode of antigen routing and presentation in DCs. Aspergillus conidia activated CD8(+) T cells upon sorting to the Rab14(+) endosomal compartment required for alternative MHC class I presentation. Cross-priming of CD8(+) T cells failed to occur in mice with CGD due to defective DC endosomal alkalinization and autophagy. However, long-lasting antifungal protection and disease control were successfully achieved upon vaccination with purified fungal antigens that activated CD4(+) T cells through the endosome/lysosome pathway. Our study thus indicates that distinct intracellular pathways are exploited for the priming of CD4(+) and CD8(+) T cells to A. fumigatus and suggests that CD4(+) T cell vaccination may be able to overcome defective antifungal CD8(+) T cell memory in individuals with CGD.