The role of T lymphocytes in myocardial ischaemia/reperfusion injury

PhD ThesisMyocardial infarction is the greatest cause of mortality worldwide, and a source of considerable morbidity. Treatment of STCelevation MI (STEMI) has improved enormously with the advent of primary percutaneous coronary intervention (PPCI), but ischaemia/reperfusion (I/R) injury remains an important complication. Evidence from animal studies points to a role for lymphocytes, and in particular T cells, in myocardial I/R injury, but this has not yet been studied in humans. The goal of my PhD was to investigate this phenomenon in human patients treated with PPCI, with particular emphasis on T cell kinetics, their relationship to I/R injury, and the potential mechanisms involved. I retrospectively analysed a large database of MI patients treated with PPCI. I demonstrated that lymphopaenia during admission was an independent predictor of increased longCterm mortality, confirming the prognostic relevance of lymphocytes in this setting for the first time. I then studied a prospectively recruited cohort of STEMI patients, determining lymphocyte subset kinetics with detailed flowCcytometric analysis. T cells were acutely depleted from the circulation within minutes of reperfusion, with highly differentiated effector cells showing the greatest changes. TransCcoronary gradients suggested some cells were sequestered into the reperfused myocardium. Cardiac MRI analysis revealed a significant relationship between postCreperfusion effector T cell kinetics and microvascular obstruction (MVO), a component of I/R injury, raising the possibility of a mechanistic link. This discovery was driven primarily by positive findings in cytomegalovirus seropositive patients, who had higher percentages of highly differentiated T cells. Analysis of chemokine receptors subsequently identified CX3CR1, with its ligand fractalkine, as the prime candidate for a key role in effector T cell kinetics postCreperfusion, potentially influencing MVO. These findings identify a possible therapeutic target in I/R injury postCPPCI, opening up a new avenue for further research and future treatment development.British Heart Foundation Clinical Research training gran

Myocardial Ischemia and Reperfusion Leads to Transient CD8 Immune Deficiency and Accelerated Immunosenescence in CMV-Seropositive Patients

Rationale: There is mounting evidence of a higher incidence of coronary heart disease (CHD) in cytomegalovirus (CMV) seropositive individuals. Objective: The aim of this study was to investigate whether acute MI triggers an inflammatory T-cell response that might lead to accelerated immunosenescence in CMV-seropositive patients. Methods and Results: Thirty-four patients with acute MI undergoing primary PCI (PPCI) were longitudinally studied within 3 months following reperfusion (Cohort A). In addition, 54 patients with acute and chronic MI were analyzed in a cross-sectional study (Cohort B). CMV-seropositive patients demonstrated a greater fall in the concentration of terminally differentiated CD8 effector memory T cells (TEMRA) in peripheral blood during the first 30 min of reperfusion compared with CMV-seronegative patients (-192 vs. -63 cells/µl; p=0.008), correlating with the expression of programmed cell death-1 (PD-1) before PPCI (r=0.8; p=0.0002). A significant proportion of TEMRA cells remained depleted for at least 3 months in CMV-seropositive patients. Using high-throughput 13-parameter flow cytometry and HLA class I CMV-specific dextramers, we confirmed an acute and persistent depletion of terminally differentiated TEMRA and CMV-specific CD8+ cells in CMV-seropositive patients. Long-term reconstitution of the TEMRA pool in chronic CMV-seropositive post-MI patients was associated with signs of terminal differentiation including an increase in KLRG1 and shorter telomere length in CD8+ T cells (2225 bp vs. 3397 bp; p<0.001). Conclusions: Myocardial ischemia and reperfusion in CMV-seropositive patients undergoing PPCI leads to acute loss of antigen-specific, terminally differentiated CD8 T-cells, possibly through PD-1-dependent programmed cell death. Our results suggest that acute MI and reperfusion accelerate immunosenescence in CMV-seropositive patients

Aspirin non-response in pregnant women at increased risk of pre-eclampsia

Objectives: Low dose aspirin (LDA) is recommended for women at increased risk of preeclampsia (PE), however it is not always effective. The study sought to determine the prevalence of non-response to LDA and to ascertain the effect of increasing aspirin dose in non-responders. Study design: Single centre, cohort study of 166 women at increased risk of PE was conducted in a large maternity unit in the UK between 2013 and 2016. All women were prescribed 75 mg of aspirin and invited to attend study visits at 18–24 weeks’ and 32–36 weeks’ gestation. Non-response was defined as a serum thromboxane B2 (TXB2) ≤10 ng/mL. Aspirin dose was increased to 150 mg if a bedside VerifyNow test suggested non-response (test value ≥ 550 arachidonic acid reactive units [ARU]) at 18–24 weeks. Adherence was assessed by self-report. Results: Based on serum TXB2, response rates were 85.3 % at 18–24 weeks and 79.3 % at 32–36 weeks’ gestation. Compared to serum TXB2, the VerifyNow test demonstrated moderate test performance (AUC 0.79 95 % CI 0.71−0.88, p < 0.0001) to detect non-response. High prevalence of non-adherence (6/10) was evident in persistent non-response group. Dose change from 75 to 150 mg of aspirin in adherent participants improved response (VerifyNow: 598 [95 % CI 550–665] ARU at 18–24 weeks on 75 mg aspirin, 509 [95 % CI 350–667] at 32–36 weeks on 150 mg of aspirin, [p < 0.0001]). Conclusions: Non-response to LDA is common in pregnancy but appears to be largely attributable to non-adherence. Dose change could be useful to improve response to LDA in this cohort

Ventilatory frequency as a measure of the response of tammar wallabies (Macropus eugenii) to the odour of potential predators

This study uses changes in ventilatory frequency to quantify the physiological response of an Australian terrestrial herbivore, the tammar wallaby (Macropus eugenii), to olfactory cues suggesting the presence of potential predators. Ventilatory frequency proved to be a quantifiable measure to assess the response of this macropod marsupial to olfactory cues. Ventilatory frequency increased from mean resting levels of 45 ± 5.1 breaths min–1 to 137 ± 11.2 breaths min–1 during the first minute of exposure to all odours. These physiological responses diminished over time, with ventilatory frequency in the first minute after introduction of the scents greater than that during the subsequent four, suggesting that the initial reaction was due to disturbance and was investigative in nature. However, the ratio of ventilatory frequency in the remaining 4 min after introduction of the odours compared with before was greater for fox (3.58 ± 0.918) and cat (2.44 ± 0.272) odours than for snake (2.27 ± 0.370), distilled water (1.81 ± 0.463) and quoll (1.71 ± 0.245) odours, suggesting that fox and cat odour provoked a greater response. However, the wallabies’ response to the odour of these introduced predators and to horse odour (2.40 ± 0.492) did not differ. Our study indicates that a long period of co-history with particular predators is not a prerequisite for detection of potentially threatening species. We do not find any support for the hypothesis that an inability to interpret olfactory cues to detect and respond to potential predation by introduced predators is responsible for the decline of these macropod marsupials