Regulatory T cells in cardiovascular diseases

Inflammation is essential in the initial development and progression of many cardiovascular diseases involving innate and adaptive immune responses. The role of CD4(+)CD25(+)FOXP3(+) regulatory T (TREG) cells in the modulation of inflammation and immunity has received increasing attention. Given the important role of TREG cells in the induction and maintenance of immune homeostasis and tolerance, dysregulation in the generation or function of TREG cells can trigger abnormal immune responses and lead to pathology. A wealth of evidence from experimental and clinical studies has indicated that TREG cells might have an important role in protecting against cardiovascular disease, in particular atherosclerosis and abdominal aortic aneurysm. In this Review, we provide an overview of the roles of TREG cells in the pathogenesis of a number of cardiovascular diseases, including atherosclerosis, hypertension, ischaemic stroke, abdominal aortic aneurysm, Kawasaki disease, pulmonary arterial hypertension, myocardial infarction and remodelling, postischaemic neovascularization, myocarditis and dilated cardiomyopathy, and heart failure. Although the exact molecular mechanisms underlying the cardioprotective effects of TREG cells are still to be elucidated, targeted therapies with TREG cells might provide a promising and novel future approach to the prevention and treatment of cardiovascular diseases.

Dynamic Frequency of Blood CD4+CD25+ Regulatory T Cells in Rats with Collagen-induced Arthritis

CD4+CD25+ regulatory T cells (CD4+CD25+ Tregs) have been shown to play a regulatory or suppressive role in the immune response and are possibly relevant to the pathogenesis of autoimmune diseases. In the present study, we attempted to investigate the frequency of CD4+CD25+ Tregs in peripheral blood (PB) of collagen-induced arthritis (CIA) rats during the development of arthritis, to determine whether their frequency is involved in the immunoregulation of this disease. The results showed that normal rats had similar frequencies of CD4+CD25+ Tregs in PB during the experiment time, expressed as a percentage of CD4+CD25+Foxp3+ T cells among the CD4+ T lymphocyte population. In contrast, the frequency of CD4+CD25+Foxp3+ T cells in CIA rats was found to change during the development of arthritis. In CIA rats, there is a significant negative correlation between the frequency of CD4+CD25+Foxp3+ T cells and paw swelling (r=-0.786, p< 0.01). The relationship between the frequency of CD4+CD25+Foxp3+ T and immune activation was not found in normal rats. During the time course, the frequency of CD4+CD25+Foxp3+ T was lower in CIA rats than in normal ones. The data suggest that the frequency of PB CD4+CD25+ Tregs may be a promising marker for arthritis activity.

Blockade of OX40/OX40 ligand to decrease cytokine messenger RNA expression in acute renal allograft rejection in vitro

AIM

The aim of this study was to investigate cytokine messenger RNA (mRNA) expression by peripheral blood mononuclear cells (PBMCs) from renal recipients experiencing acute rejection by blocking OX40-OX40L interactions with recombinant human OX40-Fc fusion protein (rhOX40Fc) in vitro.

METHODS

PBMCs were isolated from 20 recipients experiencing acute rejection episodes (rejection group) and 20 recipients with stable graft function (stable group). Levels of Th1 (interferon [IFN]-γ) and Th2 (interleukin [IL]-4) mRNA expressions by PBMCs were measured using real-time reverse transcriptase-polymerase chain reactions.

RESULTS

IFN-γ mRNA expression levels were significantly higher in the rejection than the stable group (P < .05). Levels of IL-4 mRNA expression were not significantly different. Among the rejection group, rhOX40Fc reduced significantly the expression of IFN-γ and IL-4 mRNA by anti-CD3-monoclonal antibody stimulated PBMCs (P < .05, and P < .01, respectively).

CONCLUSIONS

Blocking of the interaction between OX40 and OX40L in vitro inhibited production of Thl and Th2 type cytokines.

Lymphocyte phenotypes in wild-caught rats suggest potential mechanisms underlying increased immune sensitivity in post-industrial environments

The immune systems of wild rats and of laboratory rats can been utilized as models of the human immune system in pre-industrial and post-industrial societies, respectively. In this study, lymphocyte phenotypes in wild rats were broadly characterized, and the results were compared to those obtained by us and by others using cells derived from various strains of laboratory rats. Although not expected, the production of regulatory T cells was not apparently different in wild rats compared to laboratory rats. On the other hand, differences in expression of markers involved in complement regulation, adhesion, signaling and maturation suggest increased complement regulation and decreased sensitivity in wild-caught rats compared to laboratory rats, and point toward complex differences between the maturation of T cells. The results potentially lend insight into the pathogenesis of post-industrial epidemics of allergy and autoimmune disease.

A novel monoclonal antibody specific for canine CD25 (P4A10): selection and evaluation of canine Tregs

A monoclonal antibody (mAb), P4A10, was made to the canine interleukin-2 receptor alpha chain (IL-2Ralpha; p55; Tac antigen; CD25) to facilitate studies of canine regulatory T-cells (Treg). By non-reduced Western blot, P4A10 bound to a 55kDa protein, the size of human IL-2Ralpha. In flow cytometry assays, it reacted with a minor population of circulating dog CD3(+)CD4(+) T-cells and the majority (>60%) of in vitro PMA-Ionomycin (PMA-IO)-activated canine CD3(+) T-cells. P4A10 recognized a hematopoietic cell population enriched for FoxP3+ cells as measured by flow cytometry. The P4A10-selected fractions of T-cells had significantly increased copy numbers of CD25, FoxP3, IL-10, and TGFbeta as detected by RT-PCR (reverse transcriptase-PCR) compared to the negative fractions. The P4A10-selected cells inhibited (3)H (tritiated) thymidine incorporation in a mixed leukocyte reaction (MLR) containing responders of the same origin. P4A10-selected T-cells from fresh peripheral blood mononuclear cells had less FoxP3 (p=0.07) by qRT-PCR (quantitative RT-PCR) and were less suppressive (p=0.01) than in vitro alloantigen-activated Treg. The mAb P4A10 is specific for canine CD25 and can be used to facilitate studies of CD25+FoxP3+ Treg in this clinically relevant large animal model.

In vivo dynamical interactions between CD4 Tregs, CD8 Tregs and CD4+ CD25- cells in mice

Background

Regulatory T cells (Tregs) were shown to be central in maintaining immunological homeostasis and preventing the development of autoimmune diseases. Several subsets of Tregs have been identified to date; however, the dynamics of the interactions between these subsets, and their implications on their regulatory functions are yet to be elucidated.

Methodology/Principal Findings

We employed a combination of mathematical modeling and frequent in vivo measurements of several T cell subsets. Healthy BALB/c mice received a single injection of either hCDR1 - a tolerogenic peptide previously shown to induce Tregs, a control peptide or vehicle alone, and were monitored for 16 days. During this period, splenocytes from the treated mice were analyzed for the levels of CD4, CD25, CD8, CD28 and Foxp3. The collected data were then fitted to mathematical models, in order to test competing hypotheses regarding the interactions between the followed T cell subsets. In all 3 treatment groups, a significant, lasting, non-random perturbation of the immune system could be observed. Our analysis predicted the emergence of functional CD4 Tregs based on inverse oscillations of the latter and CD4⁺CD25⁻ cells. Furthermore, CD4 Tregs seemed to require a sufficiently high level of CD8 Tregs in order to become functional, while conversion was unlikely to be their major source. Our results indicated in addition that Foxp3 is not a sufficient marker for regulatory activity.

Conclusions/Significance

In this work, we unraveled the dynamics of the interplay between CD4, CD8 Tregs and effector T cells, using, for the first time, a mathematical-mechanistic perspective in the analysis of Treg kinetics. Furthermore, the results obtained from this interdisciplinary approach supported the notion that CD4 Tregs need to interact with CD8 Tregs in order to become functional. Finally, we generated predictions regarding the time-dependent function of Tregs, which can be further tested empirically in future work.

Is there a feudal hierarchy amongst regulatory immune cells? More than just Tregs

Nature has provided the developing immune system with several checkpoints important for the maintenance of tolerance and the prevention of autoimmunity. The regulatory mechanisms operating in the periphery of the system are mediated by subsets of regulatory cells, now considered principal contributors to peripheral tolerance. Regulatory T cells (Tregs) have received titanic interest in the past decade, placing them at the centre of immuno-suppressive reactions. However, it has become clearer that other immune suppressive cells inhibit auto-reactivity as effectively as Tregs. The function of Tregs and other regulatory cells in rheumatoid arthritis will be discussed in this review.

Increased number and function of FoxP3 regulatory T cells during experimental arthritis

OBJECTIVE

CD4+CD25+FoxP3+ regulatory T (Treg) cells are critical regulators of autoimmunity. Yet the number of Treg cells is paradoxically increased in rheumatoid arthritis (RA) patients, and Treg cells show variable activity in human studies. The objective of this study was to characterize the expansion and function of Treg cells during the initiation and progression of experimental arthritis.

METHODS

To unequivocally identify Treg cells, we crossed FoxP3gfp mice with K/BxN mice to generate arthritic mice in which Treg cells express green fluorescence protein. We examined the expansion and function of Treg cells and effector T (Teff) cells during different stages of arthritis, using flow cytometry and cell proliferation analyses.

RESULTS

In K/BxN mice, thymic selection of KRN T cells resulted in an enrichment of forkhead box P3 (FoxP3)-positive Treg cells. Treg cell numbers increased during arthritis, with significant increases in spleens and draining lymph nodes, indicating selective tropism to sites of disease. In contrast to the in vitro unresponsiveness of Treg cells when cultured alone, substantial proportions of Treg cells proliferated in both nonarthritic and arthritic mice. However, they also underwent greater apoptosis, thereby maintaining equilibrium with Teff cells. Similarly, enhanced Treg cell-suppressive activity during arthritis was offset by greater resistance by their Teff cell counterparts and antigen-presenting cells.

CONCLUSION

In this well-established model of RA, the interplay of Teff cells and Treg cells in K/BxN mice recapitulated many features of the human disease. We demonstrated an ordered expansion of Treg cells during arthritis and dynamic changes in Treg cell and Teff cell functions. By elucidating factors that govern Treg cell and Teff cell development in K/BxN(gfp) mice, we will gain insight into the pathophysiology of and develop novel therapeutics for human RA.

Myeloid dendritic cells of patients with chronic HCV infection induce proliferation of regulatory T lymphocytes

BACKGROUND & AIMS

Dendritic cells (DCs) initiate and sustain an efficient T-lymphocyte response. Chronic hepatitis C virus (HCV) infection is associated with inefficient T-cell functions that fail to eradicate the virus, so defects in DC function might be involved in HCV pathogenesis. This study analyzed the activities of myeloid DCs and distinct CD4(+) T-cell populations in samples collected from patients with HCV.

METHODS

The abilities of primary BDCA1(+) or monocyte-derived DCs from HCV patients (HCV-DC) to stimulate CD4(+), CD4(+)CD25(-), or different ratios of CD4(+)CD25(+)/CD4(+)CD25(-) T cells were evaluated in mixed lymphocyte reactions. T-cell proliferation and phenotype were evaluated by flow cytometry; cytokine production was evaluated by enzyme-linked immunosorbent assay and marker expression by polymerase chain reaction analyses.

RESULTS

HCV-DCs were poor activators of CD4(+) T cells; this defect was reversed by addition of interleukin-2, neutralization of interleukin-10, or elimination of CD4(+)CD25(+) T cells. HCV-DC stimulated proliferation of regulatory T cells (Tregs; CD4(+)CD25(+)FoxP3(+)), which limit proliferation of HCV-specific T lymphocytes. We observed an increased frequency of CD4(+)CD25(+) T cells in peripheral blood of HCV patients and that HCV-DC overexpressed a number of alternative costimulatory molecules, including PD-L1. Finally, HCV-DC stimulated expansion rather than de novo induction of FoxP3(+) Tregs.

CONCLUSIONS

Our results indicate a role for myeloid DC in expansion of Tregs to promote chronic infection of patients with HCV.