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.