Background— A chronic immune response involving proinflammatory T helper cell 1 (Th1) lymphocyte activation occurs in the atherosclerotic lesion, but whether this activation is protective or deleterious remains unclear.

Methods and Results— We modulated the immune response of the atherosclerosis-prone apolipoprotein E-deficient (apoE^−/−) mouse. Eight-week-old apoE^−/− mice were treated daily with pentoxifylline (PTX), a known inhibitor of the Th1 differentiation pathway, or PBS (control) for 4 weeks or 12 weeks. Twelve-week PTX treatment reduced atherosclerotic lesion size by 60% (P<0.01). PTX-treated mice developed lesions that were limited to the degree of fatty streaks. In contrast, control mice developed mature fibrofatty atherosclerotic lesions. In parallel, the proportion of interferon (IFN)-γ-producing Th1 splenic lymphocytes was significantly reduced by PTX, and lesion size was correlated to the proportion of IFN-γ⁺ T cells. In vitro addition of PTX to cultured spleen cells did not modify the production of IFN-γ but increased the production of IL-10 by T cells, indicating that PTX does not suppress IFN-γ production but rather blocks Th1 polarization while promoting Th2 polarization.

Conclusions— Thus, PTX protected mice from atherosclerosis by reducing the Th1 polarization of T helper lymphocytes. This study demonstrates that the Th1 immune response associated with atherosclerosis is deleterious and that a modulation of the Th1 differentiation pathway may provide a new pharmacological tool to treat this disease.