Claudia Mauri

Compromised Function of Regulatory T Cells in Rheumatoid Arthritis and Reversal by Anti-TNFα Therapy

Regulatory T cells have been clearly implicated in the control of disease in murine models of autoimmunity. The paucity of data regarding the role of these lymphocytes in human autoimmune disease has prompted us to examine their function in patients with rheumatoid arthritis (RA). Regulatory (CD4+CD25+) T cells isolated from patients with active RA displayed an anergic phenotype upon stimulation with anti-CD3 and anti-CD28 antibodies, and suppressed the proliferation of effector T cells in vitro. However, they were unable to suppress proinflammatory cytokine secretion from activated T cells and monocytes, or to convey a suppressive phenotype to effector CD4+CD25− T cells. Treatment with antitumor necrosis factor α (TNFα; Infliximab) restored the capacity of regulatory T cells to inhibit cytokine production and to convey a suppressive phenotype to “conventional” T cells. Furthermore, anti-TNFα treatment led to a significant rise in the number of peripheral blood regulatory T cells in RA patients responding to this treatment, which correlated with a reduction in C reactive protein. These data are the first to demonstrate that regulatory T cells are functionally compromised in RA, and indicate that modulation of regulatory T cells by anti-TNFα therapy may be a further mechanism by which this disease is ameliorated.

CD19+CD24hiCD38hi B Cells Exhibit Regulatory Capacity in Healthy Individuals but Are Functionally Impaired in Systemic Lupus Erythematosus Patients

The immunosuppressive function of regulatory B cells has been shown in several murine models of chronic inflammation, including collagen-induced arthritis, inflammatory bowel disease, and experimental autoimmune encephalomyelitis. Despite interest in these cells, their relevance to the maintenance of peripheral tolerance in humans remains elusive. Here, we demonstrate that human CD19(+)CD24(hi)CD38(hi) B cells possessed regulatory capacity. After CD40 stimulation, CD19(+)CD24(hi)CD38(hi) B cells suppressed the differentiation of T helper 1 cells, partially via the provision of interleukin-10 (IL-10), but not transforming growth factor-beta (TGF-beta), and their suppressive capacity was reversed by the addition of CD80 and CD86 mAbs. In addition, CD19(+)CD24(hi)CD38(hi) SLE B cells isolated from the peripheral blood of systemic lupus erythematosus (SLE) patients were refractory to further CD40 stimulation, produced less IL-10, and lacked the suppressive capacity of their healthy counterparts. Altered cellular function within this compartment may impact effector immune responses in SLE and other autoimmune disorders.

Immune Regulatory Function of B Cells

B cells are regarded for their capacity to produce antibody. However, recent advances in B cell biology have capitalized on old findings and demonstrated that B cells also release a broad variety of cytokines. As with T helper cells, B cells can be classified into subsets according to the cytokine milieu that they produce. One functional B cell subset, regulatory B cells (Bregs), has recently been shown to contribute to the maintenance of the fine equilibrium required for tolerance. Bregs restrain the excessive inflammatory responses that occur during autoimmune diseases or that can be caused by unresolved infections. Pivotal to Breg function is interleukin-10 (IL-10), which inhibits proinflammatory cytokines and supports regulatory T cell differentiation. This review reports and discusses the factors that are important for Breg differentiation and for their effector function in both mouse and human.

Anti-TNF-alpha therapy induces a distinct regulatory T cell population in patients with rheumatoid arthritis via TGF-beta

The induction of regulatory T (T reg) cells holds considerable potential as a treatment for autoimmune diseases. We have previously shown that CD4+CD25hi T reg cells isolated from patients with active rheumatoid arthritis (RA) have a defect in their ability to suppress proinflammatory cytokine production by CD4+CD25− T cells. This defect, however, was overcome after anti–tumor necrosis factor (TNF)-α antibody (infliximab) therapy. Here, we demonstrate that infliximab therapy gives rise to a CD4+CD25hiFoxP3+ T reg cell population, which mediates suppression via transforming growth factor (TGF)-β and interleukin 10, and lacks CD62L expression, thereby distinguishing this T reg cell subset from natural T reg cells present in healthy individuals and patients with active RA. In vitro, infliximab induced the differentiation of CD62L− T reg cells from CD4+CD25− T cells isolated from active RA patients, a process dependent on TGF-β. In spite of the potent suppressor capacity displayed by this CD62L− T reg cell population, the natural CD62L+ T reg cells remained defective in infliximab-treated patients. These results suggest that anti–TNF-α therapy in RA patients generates a newly differentiated population of T reg cells, which compensates for the defective natural T reg cells. Therefore, manipulation of a proinflammatory environment could represent a therapeutic strategy for the induction of T reg cells and the restoration of tolerance.

Novel Suppressive Function of Transitional 2 B Cells in Experimental Arthritis

The immune system contains natural regulatory cells important in the maintenance of tolerance. Although this suppressive function is usually attributed to CD4 regulatory T cells, recent reports have revealed an immunoregulatory role for IL-10-producing B cells in the context of several autoimmune diseases including collagen-induced arthritis. In the present study, we attribute this suppressive function to a B cell subset expressing high levels of CD21, CD23, and IgM, previously identified as transitional 2-marginal zone precursor (T2-MZP) B cells. T2-MZP B cells are present in the spleens of naive mice and increase during the remission phase of arthritis. Following adoptive transfer to immunized DBA/1 mice, T2-MZP B cells significantly prevented new disease and ameliorated established disease. The suppressive effect on arthritis was paralleled by an inhibition of Ag-specific T cell activation and a reduction in cells exhibiting Th1-type functional responses. We also provide evidence that this regulatory subset mediates its suppression through the secretion of suppressive cytokines and not by cell-to-cell contact. The ability to regulate an established immune response by T2-MZP B cells endows this subset of B cells with a striking and previously unrecognized immunoregulatory potential.

Regulatory B Cells: Origin, Phenotype, and Function

Regulatory B (Breg) cells are immunosuppressive cells that support immunological tolerance. Through the production of interleukin-10 (IL-10), IL-35, and transforming growth factor β (TGF-β), Breg cells suppress immunopathology by prohibiting the expansion of pathogenic T cells and other pro-inflammatory lymphocytes. Recent work has shown that different inflammatory environments induce distinct Breg cell populations. Although these findings highlight the relevance of inflammatory signals in the differentiation of Breg cells, they also raise other questions about Breg cell biology and phenotype. For example, what are the functional properties and phenotype of Breg cells? Can a Breg cell arise at every stage in B cell development? Is inflammation the primary requisite for Breg cell differentiation? Here, we use these questions to discuss the advances in understanding Breg cell biology, with a particular emphasis on their ontogeny; we propose that multiple Breg cell subsets can be induced in response to inflammation at different stages in development.

Mice Lacking Endogenous IL-10–Producing Regulatory B Cells Develop Exacerbated Disease and Present with an Increased Frequency of Th1/Th17 but a Decrease in Regulatory T Cells

IL-10–producing B cells, also known as regulatory B cells (Bregs), play a key role in controlling autoimmunity. In this study, we report that chimeric mice specifically lacking IL-10–producing B cells (IL-10−/−B cell) developed an exacerbated arthritis compared with chimeric wild-type (WT) B cell mice. A significant decrease in the absolute numbers of Foxp3 regulatory T cells (Tregs), in their expression level of Foxp3, and a marked increase in inflammatory Th1 and Th17 cells were detected in IL-10−/− B cell mice compared with WT B cell mice. Reconstitution of arthritic B cell deficient (μMT) mice with different B cell subsets revealed that the ability to modulate Treg frequencies in vivo is exclusively restricted to transitional 2 marginal zone precursor Bregs. Moreover, transfer of WT transitional 2 marginal zone precursor Bregs to arthritic IL-10−/− mice increased Foxp3+ Tregs and reduced Th1 and Th17 cell frequencies to levels measured in arthritic WT mice and inhibited inflammation. In vitro, IL-10+/+ B cells established longer contact times with arthritogenic CD4+CD25− T cells compared with IL-10−/− B cells in response to Ag stimulation, and using the same culture conditions, we observed upregulation of Foxp3 on CD4+ T cells. Thus, IL-10–producing B cells restrain inflammation by promoting differentiation of immunoregulatory over proinflammatory T cells.

CD19+CD24hiCD38hi B Cells Maintain Regulatory T Cells While Limiting TH1 and TH17 Differentiation

Patients with rheumatoid arthritis have fewer regulatory B cells with decreased function, which may be associated with inflammation. Regulatory B Cells Out of Joint In the theater of the adaptive immune system, B cells and T cells are the two leads. Yet, within these cell subsets are many supporting actors, including cells that regulate the function of their more illustrious counterparts. Although regulatory T cells (Tregs) have long stood center stage in the study of autoimmune disease, another subset of regulatory cells—regulatory B cells (Bregs)—remains less well understood. Flores-Borja et al. now compare the function of Bregs in both healthy individuals and patients with rheumatoid arthritis (RA), a chronic inflammatory disease of the joints. The authors found that in healthy individuals, Bregs inhibit the differentiation of naïve T cells into the proinflammatory T helper 1 (TH1) and TH2 subsets and can induce differentiation into Tregs, largely through interleukin-10 secretion. Patients with RA have fewer Bregs, and the Bregs that are present behave differently. Although they maintained the ability to inhibit TH1 cell differentiation, Bregs from RA patients could not inhibit TH17 cell differentiation or promote Treg conversion. These data suggest that in patients with active RA, defects in Bregs may contribute to autoimmunity. The relevance of regulatory B cells in the maintenance of tolerance in healthy individuals or in patients with immune disorders remains understudied. In healthy individuals, CD19+CD24hiCD38hi B cells suppress CD4+CD25− T cell proliferation as well as the release of interferon-γ and tumor necrosis factor–α by these cells; this suppression is partially mediated through the production of interleukin-10 (IL-10). We further elucidate the mechanisms of suppression by CD19+CD24hiCD38hi B cells. Healthy CD19+CD24hiCD38hi B cells inhibited naïve T cell differentiation into T helper 1 (TH1) and TH17 cells and converted CD4+CD25− T cells into regulatory T cells (Tregs), in part through the production of IL-10. In contrast, CD19+CD24hiCD38hi B cells from patients with rheumatoid arthritis (RA) failed to convert CD4+CD25− T cells into functionally suppressive Tregs or to curb TH17 development; however, they maintained the capacity to inhibit TH1 cell differentiation. Moreover, RA patients with active disease have reduced numbers of CD19+CD24hiCD38hi B cells in peripheral blood compared with either patients with inactive disease or healthy individuals. These results suggest that in patients with active RA, CD19+CD24hiCD38hi B cells with regulatory function may fail to prevent the development of autoreactive responses and inflammation, leading to autoimmunity.

The ‘short’ history of regulatory B cells

The maintenance of tolerance is the sine qua non of a sophisticated regulatory apparatus to prevent or dampen overzealous immune responses. In addition to the ability of B cells to prime and activate the immune system, B cells with regulatory function (Bregs) have been identified in experimental models of autoimmunity, infections, and cancer, supporting the notion that, similar to regulatory T cells (Tregs), Breg-mediated suppression is an important means for the maintenance of peripheral tolerance. This regulatory function appears to be directly mediated by the production of IL-10 and/or TGFbeta and by the ability of B cells to interact with pathogenic T cells to inhibit harmful immune responses. The identification of their existence is of great relevance to the understanding of autoimmune diseases and to the development of new therapeutic strategies.

Defects in CTLA-4 are associated with abnormal regulatory T cell function in rheumatoid arthritis

The ultimate goal for the treatment of autoimmunity is to restore immunological tolerance. Regulatory T cells (Treg) play a central role in immune tolerance, and Treg functional abnormalities have been identified in different autoimmune diseases, including rheumatoid arthritis (RA). We have previously shown that natural Treg from RA patients are competent at suppressing responder T cell proliferation but not cytokine production. Here, we explore the hypothesis that this Treg defect in RA is linked with abnormalities in the expression and function of CTLA-4. We demonstrate that CTLA-4 expression on Treg from RA patients was significantly reduced compared with healthy Treg and is associated with an increased rate of CTLA-4 internalization. Regulation of T cell receptor signaling by CTLA-4 was impaired in RA Treg and associated with delayed recruitment of CTLA-4 to the immunological synapse. Artificial induction of CTLA-4 expression on RA Treg restored their suppressive capacity. Furthermore, CTLA-4 blockade impaired healthy Treg suppression of T cell IFN-γ production, but not proliferation, thereby recapitulating the unique Treg defect in RA. Our results suggest that defects in CTLA-4 could contribute to abnormal Treg function in RA and may represent a target for therapy for inducing long-lasting remission.