Liuzzo, Giovanna

Background —Unstable angina (UA) is associated with systemic inflammation and with expansion of interferon-γ–producing T lymphocytes. The cause of T-cell activation and the precise role of activated T cells in plaque instability are not understood. Methods and Results —Peripheral blood T cells from 34 patients with stable angina and 34 patients with UA were compared for the distribution of functional T-cell subsets by flow cytometric analysis. Clonality within the T-cell compartment was identified by T-cell receptor spectrotyping and subsequent sequencing. Tissue-infiltrating T cells were examined in extracts from coronary arteries containing stable or unstable plaque. The subset of CD4 + CD28 null T cells was expanded in patients with UA and infrequent in patients with stable angina (median frequencies: 10.8% versus 1.5%, P <0.001). CD4 + CD28 null T cells included a large monoclonal population, with 59 clonotypes isolated from 20 UA patients. T-cell clonotypes from different UA patients used antigen receptors with similar sequences. T-cell receptor sequences derived from monoclonal T-cell populations were detected in the culprit but not in the nonculprit lesion of a patient with fatal myocardial infarction. Conclusions —UA is associated with the emergence of monoclonal T-cell populations, analogous to monoclonal gammopathy of unknown significance. Shared T-cell receptor sequences in clonotypes of different patients implicate chronic stimulation by a common antigen, for example, persistent infection. The unstable plaque but not the stable plaque is invaded by clonally expanded T cells, suggesting a direct involvement of these lymphocytes in plaque disruption.

Background —Monocytes are constitutively activated in unstable angina (UA), resulting in the production of IL-6 and the upregulation of acute phase proteins. Underlying mechanisms are not understood. To explore whether the production of the potent monocyte activator IFN-γ is altered in UA, we compared cytokine production by T lymphocytes in patients with UA (Braunwald’s class IIIB) and with stable angina (SA). Methods and Results —Peripheral blood lymphocytes were collected at the time of hospitalization and after 2 and 12 weeks. Cytokine-producing CD4 + and CD8 + T cells were quantified by 3-color flow cytometry after stimulation with phorbol myristate acetate and ionomycin. UA was associated with an increased number of CD4 + and CD8 + T cells producing IFN-γ, whereas patients with SA had higher frequencies of IL-2 + and IL-4 + CD4 + T cells. Expansion of the IFN-γ + T-cell population in UA persisted for at least 3 months. Increased production of IFN-γ in UA could be attributed to the expansion of an unusual subset of T cells, CD4 + CD28 null T cells. Conclusions —Patients with UA are characterized by a perturbation of the functional T-cell repertoire with a bias toward IFN-γ production, suggesting that monocyte activation and acute phase responses are consequences of T-cell activation. IFN-γ is produced by CD4 + CD28 null T cells, which are expanded in UA and distinctly low in SA and controls. The emergence of CD4 + CD28 null T cells may result from persistent antigenic stimulation.

Background —Activation of circulating monocytes in patients with acute coronary syndromes may reflect exposure to bacterial products or stimulation by cytokines such as IFN-γ. IFN-γ induces phosphorylation and nuclear translocation of transcription factor STAT-1, which initiates a specific program of gene induction. To explore whether monocyte activation is IFN-γ driven, patients with unstable (UA) or stable angina (SA) were compared for nuclear translocation of STAT-1 complexes and upregulation of IFN-γ–inducible genes CD64 and IP-10. Methods and Results —Peripheral blood mononuclear cells were stained for expression of CD64 on CD14 + monocytes and analyzed by PCR for transcription of IP-10. Expression of CD64 was significantly increased in patients with UA. Monocytes from UA patients remained responsive to IFN-γ in vitro, with accelerated transcriptional competency of CD64. IP-10–specific sequences were spontaneously detectable in 82% of the UA patients and 15% of SA patients ( P <0.001). Most importantly, STAT-1 complexes were found in nuclear extracts prepared from freshly isolated monocytes of patients with UA, which provides compelling evidence for IFN-γ signaling in vivo. Conclusions —Monocytes from UA patients exhibit a molecular fingerprint of recent IFN-γ triggering, such as nuclear translocation of STAT-1 complexes and upregulation of IFN-γ–inducible genes CD64 and IP-10, which suggests that monocytes are activated, at least in part, by IFN-γ. IFN-γ may derive from stimulated T lymphocytes, which implicates specific immune responses in the pathogenesis of acute coronary syndromes.