Are T cells from healthy heart really only passengers? Characterization of cardiac tissue T cells

Functional genomics analysis identifies T and NK cell activation as a driver of epigenetic clock progression

BACKGROUND

Epigenetic clocks use DNA methylation (DNAm) levels of specific sets of CpG dinucleotides to accurately predict individual chronological age. A popular application of these clocks is to explore whether the deviation of predicted age from chronological age is associated with disease phenotypes, where this deviation is interpreted as a potential biomarker of biological age. This wide application, however, contrasts with the limited insight in the processes that may drive the running of epigenetic clocks.

RESULTS

We perform a functional genomics analysis on four epigenetic clocks, including Hannum's blood predictor and Horvath's multi-tissue predictor, using blood DNA methylome and transcriptome data from 3132 individuals. The four clocks result in similar predictions of individual chronological age, and their constituting CpGs are correlated in DNAm level and are enriched for similar histone modifications and chromatin states. Interestingly, DNAm levels of CpGs from the clocks are commonly associated with gene expression in trans. The gene sets involved are highly overlapping and enriched for T cell processes. Further analysis of the transcriptome and methylome of sorted blood cell types identifies differences in DNAm between naive and activated T and NK cells as a probable contributor to the clocks. Indeed, within the same donor, the four epigenetic clocks predict naive cells to be up to 40 years younger than activated cells.

CONCLUSIONS

The ability of epigenetic clocks to predict chronological age involves their ability to detect changes in proportions of naive and activated immune blood cells, an established feature of immuno-senescence. This finding may contribute to the interpretation of associations between clock-derived measures and age-related health outcomes.

Myocardial aging as a T-cell-mediated phenomenon

In recent years, the myocardium has been rediscovered under the lenses of immunology, and lymphocytes have been implicated in the pathogenesis of cardiomyopathies with different etiologies. Aging is an important risk factor for heart diseases, and it also has impact on the immune system. Thus, we sought to determine whether immunological activity would influence myocardial structure and function in elderly mice. Morphological, functional, and molecular analyses revealed that the age-related myocardial impairment occurs in parallel with shifts in the composition of tissue-resident leukocytes and with an accumulation of activated CD4+ Foxp3- (forkhead box P3) IFN-γ+ T cells in the heart-draining lymph nodes. A comprehensive characterization of different aged immune-deficient mouse strains revealed that T cells significantly contribute to age-related myocardial inflammation and functional decline. Upon adoptive cell transfer, the T cells isolated from the mediastinal lymph node (med-LN) of aged animals exhibited increased cardiotropism, compared with cells purified from young donors or from other irrelevant sites. Nevertheless, these cells caused rather mild effects on cardiac functionality, indicating that myocardial aging might stem from a combination of intrinsic and extrinsic (immunological) factors. Taken together, the data herein presented indicate that heart-directed immune responses may spontaneously arise in the elderly, even in the absence of a clear tissue damage or concomitant infection. These observations might shed new light on the emerging role of T cells in myocardial diseases, which primarily affect the elderly population.

The role of nitric oxide in regulation of leukocyte migration into the heart tissue in vitro

Characteristics of leukocyte migration have been studied during the incubation of the right and left ventricles of rat heart explants in autologous blood plasma. Within the first 60 min, the leukocyte amount in the medium increases. Moreover, it is associated with cell release from the heart tissue. During further incubation, the cell release decreases; after 3 h of incubation, the cells begin to migrate back into the heart tissue. However, neutrophil migration does not change. Sodium nitrite, being a donor of nitric oxide significantly, reduces the leukocyte migration from the heart explants into the incubation medium, especially from left ventricle explants.

Donor CD4 T cells contribute to cardiac allograft vasculopathy by providing help for autoantibody production

BACKGROUND

The development of autoantibody after heart transplantation is increasingly associated with poor graft outcome, but what triggers its development and whether it has a direct causative role in graft rejection is not clear. Here, we study the development of antinuclear autoantibody in an established mouse model of heart allograft vasculopathy.

METHODS AND RESULTS

Humoral vascular changes, including endothelial complement staining, were present in bm12 heart grafts, explanted 50 days after transplantation. Alloantibody was not detectable, but long-lasting autoantibody responses developed in C57BL/6 recipients from the third week after transplantation. No autoantibody was generated if donor CD4 T cells were depleted before heart graft retrieval or in recipients that lacked B-cell major histocompatibility complex class II expression, indicating that humoral autoimmunity is a consequence of donor CD4 T-cell allorecognition of the major histocompatibility complex class II complex on recipient autoreactive B cells. An effector role for autoantibody in graft rejection was confirmed by abrogation of humoral vascular rejection, and attenuation of vasculopathy, in B-cell deficient recipients and by development of vascular obliteration and accelerated rejection in recipients primed for autoantibody before transplantation.

CONCLUSIONS

Passenger CD4 T cells within heart transplants can contribute to allograft vasculopathy by providing help to recipient B cells for autoantibody generation.

Interstitial leukocytes in right ventricular endomyocardial biopsies after heart transplantation in patients with complicated versus uneventful postoperative course

BACKGROUND

Infections and rejections play key roles in morbidity and mortality in the early postoperative period after orthotopic heart transplantation (HTX). The aim of this study was to evaluate whether qualitative and quantitative analyses of various interstitial leukocytes in endomyocardial biopsies during the first 2 weeks after HTX provided early information on these complications.

PATIENTS AND METHODS

During and after HTX, endomyocardial biopsies were obtained in 51 patients. By immunohistochemistry we determined the CD3-, CD4-, CD8-, CD15-, CD20-, CD57-, and CD68-positive cell numbers projected to planimetrically measured areas. To compare morbidity in the postoperative course, the patients were subdivided into complicated versus uncomplicated after 3 months.

RESULTS

In the uncomplicated group, the cell counts of CD3-, CD8-, CD57-, and CD68-positive cells were significantly lower than in the complicated group. CD3-, CD4-, and CD8-positive cell numbers showed a significant decrease in the first week among the uncomplicated group. In the complicated group, the cell counts increased significantly in the second week. The numbers of CD57-positive cells were significantly lower during the first and second weeks among the uncomplicated group.

CONCLUSIONS

Increased T lymphocytes, natural killer cells, and macrophages observed in the second week after HTX indicated increased morbidity. A reduction in CD3-positive cells in the first week indicated a low morbidity risk; an increase indicated a higher risk.