Harnessing the Therapeutic Potential of Th17 Cells

Th17 cells provide protective immunity to infections by fungi and extracellular bacteria as well as cancer but are also involved in chronic inflammation. The cells were first identified by their ability to produce interleukin 17A (IL-17A) and, subsequently, associated with chronic inflammation and autoimmunity. Th17 cells have some gene profile similarity with stem cells and can remain dormant in mucosal tissues for long periods. Indeed, recent studies suggest that functionally distinct subsets of pro- and anti-inflammatory Th17 cells can interchange phenotype and functions. For development, Th17 cells require activation of the transcription factors STAT3 and RORγt while RUNX1, c-Maf, and Aiolos are involved in changes of phenotype/functions. Attempts to harness Th17 cells against pathogens and cancer using vaccination strategies are being explored. The cells gain protective abilities when induced to produce interferon γ (IFNγ). In addition, treatment with antibodies to IL-17 is effective in treating patients with psoriasis, psoriatic arthritis, and refectory rheumatoid arthritis. Moreover, since RORγt is a nuclear receptor, it is likely to be a potential future drug target for modulating Th17 functions. This review explores pathways through which Th17 subsets are induced, the molecular basis of their plasticity, and potential therapeutic strategies for their modulation in diseases

Methionine Sulfoxide Reductase A (MsrA) Deficient Mycoplasma genitalium Shows Decreased Interactions with Host Cells

Mycoplasma genitalium is an important sexually transmitted pathogen that affects both men and women. In genital-mucosal tissues, it initiates colonization of epithelial cells by attaching itself to host cells via several identified bacterial ligands and host cell surface receptors. We have previously shown that a mutant form of M. genitalium lacking methionine sulfoxide reductase A (MsrA), an antioxidant enzyme which converts oxidized methionine (Met(O)) into methionine (Met), shows decreased viability in infected animals. To gain more insights into the mechanisms by which MsrA controls M. genitalium virulence, we compared the wild-type M. genitalium strain (G37) with an msrA mutant (MS5) strain for their ability to interact with target cervical epithelial cell lines (HeLa and C33A) and THP-1 monocytic cells. Infection of epithelial cell lines with both strains revealed that MS5 was less cytotoxic to HeLa and C33A cell lines than the G37 strain. Also, the MS5 strain was more susceptible to phagocytosis by THP-1 cells than wild type strain (G37). Further, MS5 was less able to induce aggregation and differentiation in THP-1 cells than the wild type strain, as determined by carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling of the cells, followed by counting of cells attached to the culture dish using image analysis. Finally, MS5 was observed to induce less proinflammatory cytokine TNF-α by THP-1 cells than wild type G37 strain. These results indicate that MsrA affects the virulence properties of M. genitalium by modulating its interaction with host cells

High-affinity Fc receptor expression indicates relative immaturity in human monocytes

Within monocyte heterogeneity, subsets represent discrete, well-characterised phenotypes. Although many studies have highlighted differences between subsets, there is evidence that subpopulations represent contiguous stages in a maturational series. As CD14hiCD64hi monocytes have higher proliferative potential than CD14hiCD64lomonocytes, the surface marker profile on four subsets defined by CD14 and CD64 was measured. The profiles were compared to that of subsets defined by the high affinity IgE receptor (FcεRIα), CD16 and CD14; further differences in size, granularity and buoyancy were measured in subsets delineated by these markers. There was a positive correlation between proliferative monocyte (PM) prevalence and CD64 expression on the ‘classical’ monocyte subset, and also between PM prevalence and circulating FcεRIα+monocytes. The expression of CD64, the high affinity IgG receptor, on canonical human monocyte subsets was determined before and aftershorttermculture, and in responseto IL-6, IL-10, M-CSF, GM-CSF and IFNγ;the influence of these cytokines on monocyte subset transition was also measured. The loss of FcεRIαexpression preceded an increasein CD16 expression in wholeblood cultures. These data indicate high affinity Fc receptors are expressed on less mature monocytes and that FcεRIα+ monocytes are developmentally antecedent to the canonical classical and intermediate monocyte subsets

Ibudilast inhibits chemokine expression in rheumatoid synovial fibroblasts and exhibits immunomodulatory activity in experimental arthritis

Objective: Ibudilast is a well‐tolerated, orally available type 4 phosphodiesterase (PDE4) inhibitor used to treat asthma and stroke. As PDE4 inhibition suppresses inflammatory mediator production and cell proliferation in leukocytes, ibudilast may be a valuable therapy for the treatment of inflammatory auto‐immune diseases such as rheumatoid arthritis (RA). We assessed the therapeutic potential of ibudilast by measuring its capacity to modulate inflammation in human leukocytes, RA synovial fibroblasts (RASF) and in experimental arthritis.Methods: Using standard curve‐qPCR, the effect of ibudilast on gene expression in activated human leukocytes and RASF was measured. Ibudilast was used to treat DBA/1 mice with collagen‐induced arthritis and an adoptive transfer model was used to assess its tolerogenic capacity.Results: Ibudilast inhibited the expression of TNF, IL12A and IL12B, the secretion of TNFα and IL12/23p40 from leukocytes and reduced the expression of CCL5 and CCL3 in activated RASF. Treatment of experimental arthritis with ibudilast resulted in a reduction in IL‐17‐producing cells and inhibition of disease progression. When combined with a TNF‐inhibitor, ibudilast caused marked suppression of active disease. Exposure of leukocytes from type II collagen‐immunised DBA/1 mice to ibudilast in vitro attenuated their ability to adoptively‐transfer arthritis to DBA/1J‐PrkdcSCID mice, providing evidence of an immunomodulatory effect.Conclusion: Ibudilast reduced the expression and/or secretion of inflammatory mediators from activated human leukocytes and RASF, inhibited Th17 responses in vivo and improved established arthritis. Given the established safety profile of ibudilast in man, its clinical evaluation in RA, either alone or in combination with a TNF inhibitor, should be considered

Lymphocytes: precursor frequencies

The frequency of antigen‐specific cells will vary during development and in response to the first and subsequent encounters with an antigen, either through infection or immunisation, and is an important indicator of adaptive immune function. Antigen‐specific lymphocyte prevalence can be estimated indirectly and directly using several different techniques. Functional assays have been used for several decades to indirectly calculate the frequency of antigen‐specific lymphocytes by measuring a proliferative response, cytokine production or cytolytic activity in response to antigenic stimulation. The functional activity of individual lymphocytes is also able to be measured directly, which allows phenotypic analyses of antigen‐specific cells. More recently, labelled MHC (major histocompatibility complex)/peptide multimers have allowed researchers to directly enumerate and comprehensively phenotype lymphocytes using multiparameter flow cytometry

IDO activation, inflammation and musculoskeletal disease

The IDO/kynurenine pathway is now established as a major regulator of immune system function. The initial enzyme, indoleamine 2,3-dioxygenase (IDO1) is induced by IFNγ, while tryptophan-2,3-dioxygenase (TDO) is induced by corticosteroids. The pathway is therefore positioned to mediate the effects of systemic inflammation or stress-induced steroids on tissue function and its expression increases with age. Disorders of the musculoskeletal system are a common feature of ageing and many of these conditions are characterized by an inflammatory state. In inflammatory arthritis and related disorders, kynurenine protects against the development of disease, while inhibition or deletion of IDO1 increases its severity. The long-term regulation of autoimmune disorders may be influenced by the epigenetic modulation of kynurenine pathway genes, with recent data suggesting that methylation of IDO may be involved. Osteoporosis is also associated with abnormalities of the kynurenine pathway, reflected in an inversion of the ratio between blood levels of the metabolites anthranilic acid and 3-hydroxy-anthranilic acid. This review discusses evidence to date on the role of the IDO/kynurenine pathway and the highly prevalent age-related disorders of osteoporosis and rheumatoid arthritis and identifies key areas that require further research

TNFα in the regulation of Treg and Th17 cells in rheumatoid arthritis and other autoimmune inflammatory diseases.

TNFα is a principal pro-inflammatory cytokine vital for immunity to infections. However, its excessive production is involved in chronic inflammation and disease pathology in autoimmune diseases. Evidence for its pathogenic role is validated by the fact that its neutralisation by therapeutic agents in vivo is beneficial in ameliorating disease and controlling symptoms. Paradoxically, however, treatment with TNFα inhibitors can either have no clinical effects, or even exacerbate disease in some patients. The explanation for such contradictory outcomes may lay in how and which downstream signalling pathways are activated and drive disease. TNFα causes its effects by binding to either or both of two membrane-bound receptors, TNFR1 and TNFR2. Engagement of the receptors can induce cell death or cell proliferation. T cells both produce and respond to TNFα and depending on whether the cytokine is membrane-bound or soluble and the level of expression of its two receptors, the biological outcome can be distinct. In addition, polymorphisms in genes encoding TNFα and T cell signalling proteins can significantly impact the outcome of TNFα receptor engagement. Early studies revealed that effector T cells in patients with rheumatoid arthritis (RA) are hyporesponsive due to chronic exposure to TNFα. However, recent evidence indicates that the relationship between TNFα and T cell responses is complex and, at times, can be paradoxical. In addition, there is controversy as to the specific effects of TNFα on different T cell subsets. This review will summarise knowledge on how TNFα modulates T cell responses and the effect of engaging either of its two receptors. Furthermore, we discuss how such interactions can dictate the outcome of treatment with TNFα inhibitors.Our study on TNFα in RA was supported by Research Grant No. WS872934 from Pfizer, UK