Recalling the Year in Memory T Cells

PI3K signalling in inflammation

PI3Ks regulate several key events in the inflammatory response to damage and infection. There are four Class I PI3K isoforms (PI3Kα,β,γ,δ), three Class II PI3K isoforms (PI3KC2α, C2β, C2γ) and a single Class III PI3K. The four Class I isoforms synthesise the phospholipid 'PIP3'. PIP3 is a 'second messenger' used by many different cell surface receptors to control cell movement, growth, survival and differentiation. These four isoforms have overlapping functions but each is adapted to receive efficient stimulation by particular receptor sub-types. PI3Kγ is highly expressed in leukocytes and plays a particularly important role in chemokine-mediated recruitment and activation of innate immune cells at sites of inflammation. PI3Kδ is also highly expressed in leukocytes and plays a key role in antigen receptor and cytokine-mediated B and T cell development, differentiation and function. Class III PI3K synthesises the phospholipid PI3P, which regulates endosome-lysosome trafficking and the induction of autophagy, pathways involved in pathogen killing, antigen processing and immune cell survival. Much less is known about the function of Class II PI3Ks, but emerging evidence indicates they can synthesise PI3P and PI34P2 and are involved in the regulation of endocytosis. The creation of genetically-modified mice with altered PI3K signalling, together with the development of isoform-selective, small-molecule PI3K inhibitors, has allowed the evaluation of the individual roles of Class I PI3K isoforms in several mouse models of chronic inflammation. Selective inhibition of PI3Kδ, γ or β has each been shown to reduce the severity of inflammation in one or more models of autoimmune disease, respiratory disease or allergic inflammation, with dual γ/δ or β/δ inhibition generally proving more effective. The inhibition of Class I PI3Ks may therefore offer a therapeutic opportunity to treat non-resolving inflammatory pathologies in humans. This article is part of a Special Issue entitled Phosphoinositides.

T(H)1, T(H)2, and T(H)17 cells instruct monocytes to differentiate into specialized dendritic cell subsets

Monocytes and T helper (T(H)) cells rapidly infiltrate inflamed tissues where monocytes differentiate into inflammatory dendritic cells (DCs) through undefined mechanisms. Our studies indicate that T(H) cells frequently interact with monocytes in inflamed skin and elicit the differentiation of specialized DC subsets characteristic of these lesions. In psoriasis lesions, T(H)1 and T(H)17 cells interact with monocytes and instruct these cells to differentiate into T(H)1- and T(H)17-promoting DCs, respectively. Correspondingly, in acute atopic dermatitis, T(H)2 cells interact with monocytes and elicit the formation of T(H)2-promoting DCs. DC formation requires GM-CSF and cell contact, whereas T(H) subset specific cytokines dictate DC function and the expression of DC subset specific surface molecules. Moreover, the phenotypes of T cell-induced DC subsets are maintained after subsequent stimulation with a panel of TLR agonists, suggesting that T(H)-derived signals outweigh downstream TLR signals in their influence on DC function. These findings indicate that T(H) cells govern the formation and function of specialized DC subsets.

Immunologic analysis and serum heavy metal levels in exacerbated Tourette syndrome

Tourette syndrome (TS) is a childhood-onset and relapsing disorder characterized by involuntary simple or complex tics and high co-morbidity with behavioral anomalies. Its pathophysiologic mechanisms remain unclarified. We investigated immunologic alternations and serum heavy metal levels in patients with TS to elucidate the unclarified mechanisms. Based on the Yale Global Tic Severity Scale, fifteen TS subjects (four females) aged 8-34 (mean: 15.4 +/- 6.7) in exacerbation with mean severity score 40.3 +/- 14.6 were enrolled in this study. The immunoglobulin levels were normal except for higher immunoglobulin E levels (in 10 patients) with atopy. In exacerbation, there were reverse CD4/CD8 (in two), higher percentages of natural killer cells (in five) and memory T cells (in eight), diminished lymphocyte activation CD69 marker (in three) and impaired NK cytotoxicity (in six) that showed a trend of lower inhibitory CD94 (NKG2A), activating NKp46, and perforin expression compared to those of patients with stable TS and healthy controls, but similar granzyme expression. Serum ASLO, mycoplasma antibody and the levels of heavy metals were not significantly different. All aforementioned immune alterations returned to the normal ranges except for the consistently higher memory T cells. Our study demonstrated that, in some patients with TS, consistently higher memory T cells and lower cytotoxicity in exacerbation status reflect immune alterations and underscore the potential for immunomodulation or immunosuppressive treatment.

IL-7, but not thymic stromal lymphopoietin (TSLP), during priming enhances the generation of memory CD4+ T cells

Multiple activation signals (including antigen, co-stimulation, and cytokines) during T-cell priming affect the subsequent generation of memory T cells, whose survival is maintained by IL-7 and IL-15. Since the IL-7 receptor is highly expressed not only on the surface of memory T cells but also on naïve T cells, we propose that early exposure to IL-7 during priming of naïve T cells may promote their survival, and thus enhances the generation of memory cells. To test this hypothesis, TCR transgenic OT-II CD4(+) T cells were stimulated in vitro with OVA(323-339) peptide presented by syngeneic antigen-presenting cells (APCs). IL-7 or an IL-7 like cytokine, thymic stromal lymphopoietin (TSLP), was added at the initial 2-day cultivation stage. We found that a short exposure to IL-7 or TSLP during priming did not affect activation, proliferation, and glucose uptake by CD4(+) T cells compared to controls when examined on culture day 6. However, the same 6-day cultures showed that IL-7 (but not TSLP) significantly decreased the frequency of apoptotic CD4(+) T cells compared to controls. More importantly, an adoptive transfer of the 6-day primed OT-II T cells into CD45.1(+) congenic mice demonstrated that IL-7 (but not TSLP) elevated by 3- and 4-fold the number of transferred CD4(+) T cells in spleen (p<0.05) and lymph nodes (p<0.05), respectively, compared to controls. Almost all transferred CD4(+) T populations displayed phenotypes of effector (CD44(+)CD62L(-)) or central (CD44(+)CD62L(+)) memory T cells. We thus conclude that exposure of CD4(+) T cells to IL-7 during priming results in an increased frequency of CD4(+) memory T cells.