T lymphocytes inhibit the vascular response to injury.

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Abstract
The proliferation of vascular smooth muscle cells is controlled by specific growth factors and cytokines acting in paracrine networks. Macrophage products such as the platelet-derived growth factor and interleukin 1 promote smooth muscle proliferation and are released in the arterial wall during atherosclerosis and repair processes. T lymphocytes are also present in vascular tissue, but their role in vascular growth control in vivo has been unclear. We now demonstrate that rats in which T lymphocytes have been eliminated by a monoclonal antibody develop larger proliferative arterial lesions after balloon-catheter injury. Larger lesions also develop in athymic rnu/rnu rats that lack T lymphocytes, when compared with rnu/+ littermates with normal T-cell levels. Finally, injection of the lymphokine interferon gamma inhibits smooth muscle proliferation and results in smaller lesions compared with controls injected with buffer alone. These results indicate that T lymphocytes modulate smooth muscle proliferation during vascular repair. We propose that T lymphocytes may play an important, immunologically nonspecific role in tissue repair processes.