Suppression of innate and adaptive B cell activation pathways by antibody coengagement of FcγRIIb and CD19

The Fc receptor (FcγRIIb) inhibits B cell responses when coengaged with B cell receptor (BCR), and has become a target for new autoimmune disease therapeutics. For example, BCR and FcγRIIb coengagement via the Fc-engineered anti-CD19 XmAb5871 suppresses humoral immune responses. We now assess effects of XmAb5871 on other activation pathways, including the pathogen-associated molecular pattern receptor, TLR9. Since TLR9 signaling is implicated in autoimmune diseases, we asked if XmAb5871 could inhibit TLR9 costimulation. We show that XmAb5871 decreases ERK and AKT activation, cell proliferation, cytokine, and IgG production induced by BCR and/or TLR9 signals. XmAb5871 also inhibited differentiation of citrullinated peptide-specific plasma cells from rheumatoid arthritis patients. XmAb5871 may therefore have potential to suppress pathogenic B cells in autoimmune diseases.     

IL-32γ induces chemotaxis of activated T cells via dendritic cell-derived CCL5

Interleukin (IL)-32 has been associated with a variety of inflammatory diseases including rheumatoid arthritis, vasculitis and Crohn’s disease. We have previously reported that IL-32γ, the IL-32 isoform with the highest biological activity, could act as an immune modulator through regulation of dendritic cell (DC) functions in immune responses. Cell locomotion is crucial for induction of an effective immune response. In this study, we investigated the effect and underlying mechanisms of IL-32γ on recruitment of T cells. IL-32γ upregulated the expression of several chemokines including CCL2, CCL4, and CCL5 in the DCs. In particular, IL-32γ significantly increased CCL5 expression in a dose-dependent manner. Treatment with JNK and NF-κB inhibitors suppressed IL-32γ-induced CCL5 expression in DCs, indicating that IL-32γ induced CCL5 production through the JNK and NF-κB pathways. Furthermore, supernatants from IL-32γ-treated DCs showed chemotactic activities controlling migration of activated CD4⁺ and CD8⁺ T cells, and these activities were suppressed by addition of neutralizing anti-CCL5 antibody. These results show that IL-32γ effectively promotes migration of activated T cells via CCL5 production in DCs. The chemotactic potential of IL-32γ may explain the pro-inflammatory effects of IL-32 and the pathologic role of IL-32 in immune disorders such as rheumatoid arthritis.     

Anti-inflammatory intravenous immunoglobulin (IVIg) suppresses homeostatic proliferation of B cells

An intravenous injection of plasma-derived immunoglobulins is used for the treatment of severe infectious and autoimmune disorders. Despite of its clinical efficacy, precise mechanisms by which intravenous immunoglobulin (IVIg) suppresses proinflammatory immune response are still enigmatic. Here, we provide in vitro evidence that IVIg inhibits homeostatic proliferation of B cells accompanied by induction of their cell aggregation. The IVIg-driven suppression of B cell proliferation and induction of cell aggregation are both unaffected by treatment with a neutralizing antibody against low-affinity Fc receptors for IgG (CD16/FcγRIII and CD32/FcγRII), known cell surface ligands for IVIg. Our observations propose a new immunosuppressive action of IVIg, which directly acts on steady-state B cells to suppress their homeostatic expansion.     

Suppression of proteoglycan-induced arthritis by anti-CD20 B Cell depletion therapy is mediated by reduction in autoantibodies and CD4+ T cell reactivity

B cells have been implicated in the pathogenesis of rheumatoid arthritis (RA) since the discovery of RA as an autoimmune disease. There is renewed interest in B cells in RA based on the clinical efficacy of B cell depletion therapy in RA patients. Although, reduced titers of rheumatoid factor and anti-cyclic citrullinated peptide Abs are recorded, the mechanisms that convey clinical improvement are incompletely understood. In the proteoglycan-induced arthritis (PGIA) mouse model of RA, we reported that Ag-specific B cells have two important functions in the development of arthritis. PG-specific B cells are required as autoantibody-producing cells as well as Ag-specific APCs. Herein we report on the effects of anti-CD20 mAb B cell depletion therapy in PGIA. Mice were sensitized to PG and treated with anti-CD20 Ab at a time when PG-specific autoantibodies and T cell activation were evident but before acute arthritis. In mice treated with anti-CD20 mAb, development of arthritis was significantly reduced in comparison to control mAb-treated mice. B cell depletion reduced the PG-specific autoantibody response. Furthermore, there was a significant reduction in the PG-specific CD4(+) T cell recall response as well as significantly fewer PG-specific CD4(+) T cells producing IFN-gamma and IL-17, but not IL-4. The reduction in PG-specific T cells was confirmed by the inability of CD4(+) T cells from B cell-depleted mice to adoptively transfer disease into SCID mice. Overall, B cell depletion during PGIA significantly reduced disease and inhibited both autoreactive B cell and T cell function.     

Absence of Tec family kinases interleukin-2 inducible T cell kinase (Itk) and Bruton's tyrosine kinase (Btk) severely impairs Fc epsilonRI-dependent mast cell responses

Mast cells are critical effector cells in the pathophysiology of allergic asthma and other IgE-mediated diseases. The Tec family of tyrosine kinases Itk and Btk serve as critical signal amplifiers downstream of antigen receptors. Although both kinases are expressed and activated in mast cells following FcεRI stimulation, their individual contributions are not clear. To determine whether these kinases play unique and/or complementary roles in FcεRI signaling and mast cell function, we generated Itk and Btk double knock-out mice. Analyses of these mice show decreased mast cell granularity and impaired passive systemic anaphylaxis responses. This impaired response is accompanied by a significant elevation in serum IgE in Itk/Btk double knock-out mice. In vitro analyses of bone marrow-derived mast cells (BMMCs) indicated that Itk/Btk double knock-out BMMCs are defective in degranulation and cytokine secretion responses downstream to FcεRI activation. These responses were accompanied by a significant reduction in PLCγ2 phosphorylation and severely impaired calcium responses in these cells. This defect also results in altered NFAT1 nuclear localization in double knock-out BMMCs. Network analysis suggests that although they may share substrates, Itk plays both positive and negative roles, while Btk primarily plays a positive role in mast cell FcεRI-induced cytokine secretion.     

MIP-1δ activates NFATc1 and enhances osteoclastogenesis: involvement of both PLCγ2 and NFκB signaling

Pathological bone resorption is a source of significant morbidity in diseases affecting the skeleton such as rheumatoid arthritis, periodontitis, and cancer metastasis to bone. Evidence indicates that elevated levels of inflammatory mediators such as IL-1, IL-6, and TNF-α play a role in this process by promoting the formation of bone-resorbing osteoclasts. Additionally, current studies have identified inflammatory chemokines of the macrophage inflammatory protein (MIP) family as potential mediators of pathological bone resorption, where both MIP-1α and -3α have been shown to enhance osteoclast (OCL) development. In this study we provide evidence that MIP-1δ, whose expression is associated with renal cell carcinoma bone metastasis and rheumatoid arthritis, enhances OCL formation in vitro via a direct effect on OCL precursors. Consistent with this ability, exposure of OCL precursors to MIP-1δ resulted in the activation of PLCγ2 and NF-κB, two signaling pathways known to regulate OCL differentiation. Moreover, MIP-1δ induced expression and nuclear translocation of NFATc1, a master regulator of osteoclastogenesis, which was dependent on activation of both the PLCγ2 and NFκB signaling pathways. Lastly, consistent with in vitro studies, in vivo administration of MIP-1δ significantly increased OCL number and resorption area as determined using a murine calvarial bone resorption model. Taken together, these data highlight the potential of MIP-1δ as a mediator of pathological bone resorption and provide insight into the molecular mechanism through which MIP-1δ enhances osteoclastogenesis.     

FcγRIIb and BAFF differentially regulate peritoneal B1 cell survival

B1 cells produce most natural Abs in unimmunized mice and play a key role in the response to thymus-independent Ags and microbial infection. Enlargement of B1 cell number in mice is often associated with autoimmunity. However, the factors that control peripheral B1 cell survival remain poorly characterized. Mice lacking the inhibitory receptor FcγRIIb exhibit a massive expansion in peritoneal B1 cells, implicating this receptor in B1 cell homeostasis. In this study, we show that peritoneal B1 cells express the highest levels of FcγRIIb among B cell subsets and are highly susceptible to FcγRIIb-mediated apoptosis. B1 cells upregulate FcγRIIb in response to innate signals, including CpG, and the B cell homeostatic cytokine BAFF efficiently protects activated B1 cells from FcγRIIb-mediated apoptosis via receptor downregulation. BAFF-transgenic mice manifest an expansion of peritoneal B1 cells that express lower levels of FcγRIIb and exhibit reduced susceptibility to apoptosis. Whereas both peritoneal B1 cells from wild-type and BAFF-transgenic mice immunized with CpG exhibit an increase in FcγRIIb levels, this change is blunted in BAFF-transgenic animals. Our combined results demonstrate that FcγRIIb controls peritoneal B1 cell survival and this program can be modulated by the BAFF signaling axis.     

Bruton's tyrosine kinase is required for TLR-induced IL-10 production

Bruton's tyrosine kinase (Btk) is a critical signaling mediator downstream of the B cell Ag receptor. X-linked agammaglobulinemia is caused by mutations in Btk resulting in multiple defects in B cell development and function, and recurrent bacterial infections. Recent evidence has also supported a role for Btk in TLR signaling. We demonstrate that Btk is activated by TLR4 in primary macrophages and is required for normal TLR-induced IL-10 production in multiple macrophage populations. Btk-deficient bone marrow-derived macrophages secrete decreased levels of IL-10 in response to multiple TLR ligands, compared with wild-type (WT) cells. Similarly, Btk-deficient peritoneal and splenic macrophages secrete decreased IL-10 levels compared with WT cultures. This phenotype correlates with Btk-dependent induction of NF-kappaB and AP-1 DNA binding activity, and altered commensal bacteria populations. Decreased IL-10 production may be responsible for increased IL-6 because blocking IL-10 in WT cultures increased IL-6 production, and supplementation of IL-10 to Btk-deficient cultures decreased IL-6 production. Similarly, injection of IL-10 in vivo with LPS decreases the elevated IL-6 serum levels during endotoxemia in Btk-deficient mice. These data further support a role for Btk in regulating TLR-induced cytokine production from APCs and provide downstream targets for analysis of Btk function.     

Interleukin-6 Receptor Blockade Selectively Reduces IL-21 Production by CD4 T Cells and IgG4 Autoantibodies in Rheumatoid Arthritis

Interleukin-6 (IL-6) levels are known to be increased in patients with rheumatoid arthritis (RA). Tocilizumab, a monoclonal antibody to the IL-6 receptor (IL-6R), reduces disease activity in RA, although its mechanisms of action remain unclear. Since IL-6 regulates cytokine production by CD4 T cells during activation, we investigated whether treatment with tocilizumab altered the phenotype and cytokine production by CD4 T cells in patients with rheumatoid arthritis. We show here that tocilizumab treatment does not change the production of cytokines by naïve CD4 T cells. However, tocilizumab treatment causes a selective decrease of IL-21 production by memory/activated CD4 T cells. Since IL-21 is known to promote plasma cell differentiation, we examined the effect of tocilizumab on the production of autoantibodies. We show that there is a decrease in the levels of IgG4 anti-CCP antibodies, but there is no effect on IgG1 anti-CCP antibodies. In addition, we show that IL-21 is a powerful inducer of IgG4 production by B cells. Thus, IL-6 contributes to the presence of IgG4-specific anti-CCP autoantibodies in RA patients, likely through its effect on IL-21 production by CD4 T cells, and IL-6R blockade down-regulates this pathway.     

Antibody-mediated coengagement of FcγRIIb and B cell receptor complex suppresses humoral immunity in systemic lupus erythematosus

Engagement of the low-affinity Ab receptor FcγRIIb downregulates B cell activation, and its dysfunction is associated with autoimmunity in mice and humans. We engineered the Fc domain of an anti-human CD19 Ab to bind FcγRIIb with high affinity, promoting the coengagement of FcγRIIb with the BCR complex. This Ab (XmAb5871) stimulated phosphorylation of the ITIM of FcγRIIb and suppressed BCR-induced calcium mobilization, proliferation, and costimulatory molecule expression of human B cells from healthy volunteers and systemic lupus erythematosus (SLE) patients, as well as B cell proliferation induced by LPS, IL-4, or BAFF. XmAb5871 suppressed humoral immunity against tetanus toxoid and reduced serum IgM, IgG, and IgE levels in SCID mice engrafted with SLE or healthy human PBMC. XmAb5871 treatment also increased survival of mice engrafted with PBMC from a unique SLE patient. Unlike anti-CD20 Ab, coengagement of FcγRIIb and BCR complex did not promote B cell depletion in human PBMC cultures or in mice. Thus, amplification of the FcγRIIb inhibitory pathway in activated B cells may represent a novel B cell-targeted immunosuppressive therapeutic approach for SLE and other autoimmune diseases that should avoid the complications associated with B cell depletion.     

Interleukin-17: the missing link between T-cell accumulation and effector cell actions in rheumatoid arthritis?

The prominence of T cells and monocyte/macrophages in rheumatoid synovium suggests T cells may localize and amplify the effector functions of monocyte/macrophages in rheumatoid disease. However, while T cells are abundant in rheumatoid joints, classic T-cell derived cytokines are scarce, especially when compared to the levels of monokines IL-1 beta and TNF-alpha. For this reason, it has been speculated that monocyte/macrophages may act independently of T cells in rheumatoid disease and that the role of T cells may be more or less irrelevant to core disease mechanisms. The question of T-cell influence requires re-evaluation in light of the characterization of IL-17, a T-cell derived cytokine that is abundant in rheumatoid synovium and synovial fluid. IL-17 has a number of pro-inflammatory effects, both directly and through amplification of the effects of IL-1 beta and TNF-alpha. IL-17 is able to induce expression of pro-inflammatory cytokines and stimulate release of eicosanoids by monocytes and synoviocytes. Furthermore, IL-17 has been implicated in the pathogenesis of inflammatory bone and joint damage through induction of matrix metalloproteinases and osteoclasts, as well as inhibition of proteoglycan synthesis. In animal models of arthritis, intra-articular injection of IL-17 results in joint inflammation and damage. The recognition of IL-17 as a pro-inflammatory T cell derived cytokine, and its abundance within rheumatoid joints, provides the strongest candidate mechanism to date through which T cells can capture and localize macrophage effector functions in rheumatoid arthritis. As such, IL-17 warrants consideration for its potential as a therapeutic target in rheumatoid arthritis.     

Anergic cells generated by blocking CD28 and CD40 costimulatory pathways in vitro ameliorate collagen induced arthritis

Collagen type II induced arthritis is an experimental model for studying the pathological mechanisms of therapeutic agents for human rheumatoid arthritis. In this study, we have investigated the effects of anergic cells on the development and disease progression of CIA. Anergic cells inhibited the proliferative response to collagen II primed lymphocytes, whereas the supernatant from anergic cell culture had no suppressive effect. Administration of anergic cells reduced the clinical score of CIA and ameliorated the development of CIA. The messenger RNA levels of IL-2 and IFN-γ were significantly decreased, whereas mRNA levels of IL-4, IL-10 and TGF-β showed no significant differences. A decrease in the collagen-specific Th1 associated IgG_2a response was observed, whereas IgG₁ was unaffected. This effective treatment is associated with a reduction in IFN-γ production and through cell-cell contact. Our results suggest that anergic cells may be beneficial for the treatment of rheumatoid arthritis.     

Combined autoimmune models of arthritis reveal shared and independent qualitative (binary) and quantitative trait loci

Collagen-induced arthritis (CIA) and proteoglycan-induced arthritis (PGIA) are murine models for rheumatoid arthritis both in terms of their pathology and genetics. Using the F(2) hybrids of the CIA-susceptible, but PGIA-resistant DBA/1 mice, and the CIA-resistant, but PGIA-susceptible BALB/c mice, our goals were to 1) identify both model-specific and shared loci that confer disease susceptibility, 2) determine whether any pathophysiological parameters could be used as markers that distinguish between nonarthritic and arthritic mice, and 3) analyze whether any immune subtraits showed colocalization with arthritis-related loci. To identify chromosomal loci, we performed a genome scan on 939 F(2) hybrid mice. For pathophysiological analyses, we measured pro- and anti-inflammatory cytokines (IL-1, IL-6, TNF-alpha, IFN-gamma, IL-4, IL-10, IL-12), Ag-specific T cell proliferation and IL-2 production, serum IgG1 and IgG2 levels of both auto- and heteroantibodies, and soluble CD44. In addition to multiple CIA- and PGIA-related loci identified in previous studies, we have identified nine new CIA- and eight new PGIA-linked loci. Comprehensive statistical analysis demonstrated that IL-2 production, T cell proliferation, and IFN-gamma levels differed significantly between arthritic and nonarthritic animals in both CIA and PGIA populations. High levels of TNF-alpha, IFN-gamma, IL-2, and Ab production were detected in F(2) hybrids with CIA, whereas T cell proliferation, IL-2 and IFN-gamma production, and a shift to IgG2a isotype were more characteristic of PGIA. Quantitative trait loci analysis demonstrated colocalization of numerous immune subtraits with arthritis-related traits. Quantitative trait loci on chromosomes 5, 10, 17, 18, and X were found to control arthritis in both models.     

Bruton's tyrosine kinase separately regulates NFkappaB p65RelA activation and cytokine interleukin (IL)-10/IL-12 production in TLR9-stimulated B Cells

B lymphocytes express both B cell receptor and Toll-like receptors (TLR). We show here that Bruton's tyrosine kinase (Btk), a critical component in B cell receptor signaling, is also involved in TLR9 signaling in B cells. Stimulation of B cells with TLR9 ligand CpG oligodeoxynucleotide (ODN) leads to transient phosphorylation of Btk, and in the absence of Btk, TLR9-induced proliferation of B cells is impaired. Interestingly, Btk(-/-) B cells secrete significantly more interleukin (IL)-12 but much less IL-10 compared with wild type B cells upon TLR9 stimulation. Immunization of Btk(-/-) mice with CpG ODN also leads to elevated levels of IL-12 in vivo and consequently, a greater -fold increment in the production of Th1 type IgG2b and IgG3 antibodies in these mice compared with wild type controls. The addition of exogenous recombinant IL-10 could suppress IL-12 production by TLR9-activated Btk(-/-) B cells, suggesting that in B cells, Btk negatively regulates IL-12 through the induction of autocrine IL-10 production. TLR9 signaling also leads to the activation of NFkappaB, including the p65RelA subunit in wild type B cells. The lack of Btk signaling affects the activation of NFkappaB and impairs the translocation of the p65RelA subunit to the nucleus of B cells upon TLR9 stimulation. However, p65RelA(-/-) B cells could respond similarly to wild type B cells in terms of IL-10 and IL-12 secretion when stimulated with CpG ODN, suggesting that the defect in NFkappaB p65RelA activation is additional to the impairment in cytokine production in TLR9-activated Btk(-/-) B cells. Thus, Btk plays an important role in TLR9 signaling and acts separately to regulate NFkappaB RelA activation as well as IL-10 and IL-12 production in B cells.     

Mononuclear phagocyte system complement receptor dysfunction in rheumatoid arthritis

To explore the relationship between complement-dependent and Fc receptor-mediated clearance mechanisms, clearance studies were performed in nine patients with definite rheumatoid arthritis and 49 normal controls. Kinetic analysis allowed evaluation of the four rate constants governing both complement- and Fc-mediated clearance processes. This analysis revealed that patients with rheumatoid arthritis had significantly reduced values for the constants regulating complement-dependent clearance (p less than 0.001). Complement-mediated clearance dysfunction was associated with normal serum complement levels and normal Fc receptor function. These data indicate that complement-mediated clearance defects are neither the simple result of a hypocomplementemic complement opsonization deficiency nor merely the reflection of profound Fc dysfunction. Defects in the two clearance processes can occur independently. These data demonstrate a specific complement receptor defect in the fixed tissue macrophages of patients with rheumatoid arthritis.     

IL-32gamma induces the maturation of dendritic cells with Th1- and Th17-polarizing ability through enhanced IL-12 and IL-6 production

IL-32, a newly described multifunctional cytokine, has been associated with a variety of inflammatory diseases, including rheumatoid arthritis, vasculitis, and Crohn's disease. In this study, we investigated the immunomodulatory effects of IL-32γ on bone marrow-derived dendritic cell (DC)-driven Th responses and analyzed the underlying signaling events. IL-32γ-treated DCs exhibited upregulated expression of cell-surface molecules and proinflammatory cytokines associated with DC maturation and activation. In particular, IL-32γ treatment significantly increased production of IL-12 and IL-6 in DCs, which are known as Th1- and Th17-polarizing cytokines, respectively. This increased production was inhibited by the addition of specific inhibitors of the activities of phospholipase C (PLC), JNK, and NF-κB. IL-32γ treatment increased the phosphorylation of JNK and the degradation of both IκBα and IκBβ in DCs, as well as NF-κB binding activity to the κB site. The PLC inhibitor suppressed NF-κB DNA binding activity and JNK phosphorylation increased by IL-32γ treatment, thereby indicating that IL-32γ induced IL-12 and IL-6 production in DCs via a PLC/JNK/NF-κB signaling pathway. Importantly, IL-32γ-stimulated DCs significantly induced both Th1 and Th17 responses when cocultured with CD4(+) T cells. The addition of a neutralizing anti-IL-12 mAb abolished the secretion of IFN-γ in a dose-dependent manner; additionally, the blockage of IL-1β and IL-6, but not of IL-21 or IL-23p19, profoundly inhibited IL-32γ-induced IL-17 production. These results demonstrated that IL-32γ could effectively induce the maturation and activation of immature DCs, leading to enhanced Th1 and Th17 responses as the result of increased IL-12 and IL-6 production in DCs.     

Amelioration of collagen-induced arthritis by blockade of inducible costimulator-B7 homologous protein costimulation

B7 homologous protein (B7h)/B7-related protein 1 (B7RP-1) is a new member of the B7 family of costimulatory molecules that specifically interacts with inducible costimulator (ICOS) expressed on activated T cells. Collagen type II (CII)-induced arthritis (CIA) is an experimental model of arthritis that has been used to dissect the pathogenesis of human rheumatoid arthritis. In this study, we have investigated the effect of neutralizing anti-B7h mAb on the development and disease progression of CIA. Administration of anti-B7h mAb significantly ameliorated the disease as assessed by clinical arthritis score and histology in the joints, and a beneficial effect was also obtained by a delayed treatment after the onset of disease. Expression of ICOS and B7h was observed in the inflamed synovial tissue as well as in the draining lymph nodes (LNs) and expansion of ICOS(+) T cells in the LN was reduced by the anti-B7h mAb treatment. Expression of mRNA for proinflammatory cytokines such as TNF-alpha, IL-1beta, and IL-6 in the joints was inhibited by the treatment. Proliferative responses and production of IFN-gamma and IL-10 upon restimulation with CII in vitro were significantly inhibited in LN cells from the anti-B7h mAb-treated mice. Serum anti-CII IgG1, IgG2a, and IgG2b levels were also reduced. Our present results showed a beneficial effect of the B7h blockade on CIA through anti-inflammatory actions and inhibition of both Th1- and Th2-mediated immune responses, suggesting that the ICOS-B7h interaction plays an important role in the pathogenesis of CIA and thus the blockade of this pathway may be beneficial for the treatment of human rheumatoid arthritis.     

调节性B细胞的发现和研究进展

B细胞主要通过呈递抗原和产生抗体发挥免疫调节作用.新近研究表明,一种全新的B细胞亚群--调节性B细胞(regulatory B cell,Bregs),可通过产生白细胞介素10(IL-10)或转化生长因子β1(TGF-β1)等抑制性细胞因子介导免疫耐受,抑制过度炎症反应.Bregs在一些慢性炎性疾病包括肠炎、类风湿性关节炎、实验性自身免疫脑脊髓炎、多发性硬化症、感染和肿瘤等发生、发展和转归过程起重要调节作用.Bregs的发现和作用机制的阐明,将为全面、深入了解免疫耐受的机制,寻找和开发更合理治疗慢性炎性疾病的策略提供理论依据.本文综述了Bregs的发现、生物学特征、发育调节及其参与炎性疾病发病的作用和机制.     

IL-23 Dependent and Independent Stages of Experimental Arthritis: No Clinical Effect of Therapeutic IL-23p19 Inhibition in Collagen-induced Arthritis

IL-23p19 deficient mice have revealed a critical role of IL-23 in the development of experimental autoimmune diseases, such as collagen-induced arthritis (CIA). Neutralizing IL-23 after onset of CIA in rats has been shown to reduce paw volume, but the effect on synovial inflammation and the immunological autoimmune response is not clear. In this study, we examined the role of IL-23 at different stages of CIA and during T cell memory mediated flare-up arthritis with focus on changes in B cell activity and Th1/Th17 modulation. Anti-IL-23p19 antibody (anti-IL23p19) treatment, starting 15 days after the type II collagen (CII)-immunization but before clinical signs of disease onset, significantly suppressed the severity of CIA. This was accompanied with significantly lower CII-specific IgG1 levels and lower IgG2a levels in the anti-IL-23p19 treated mice compared to the control group. Importantly, neutralizing IL-23 after the first signs of CIA did not ameliorate the disease. This was in contrast to arthritic mice that underwent an arthritis flare-up since a significantly lower disease score was observed in the IL-23p19 treated mice compared to the control group, accompanied by lower synovial IL-17A and IL-22 expression in the knee joints of these mice. These data show IL-23-dependent and IL-23-independent stages during autoimmune CIA. Furthermore, the memory T cell mediated flare-up arthritis is IL-23-mediated. These data suggest that specific neutralization of IL-23p19 after onset of autoimmune arthritis may not be beneficial as a therapeutic therapy for patients with rheumatoid arthritis (RA). However, T cell mediated arthritis relapses in patients with RA might be controlled by anti-IL-23p19 treatment.