Aorta contains extractable immunosuppressant activity.

A low MW fraction (approximately 3500 to 10,000 daltons) extracted from bovine aorta exerted significant dose-dependent inhibition of both human and murine lymphocyte responses to the mitogen Con A. These results do not appear to be due to nonspecific cytotoxicity, since the established cell lines BHK-21 and L-929 cells are unaffected. The inhibition of mitogenic responsivity is dependent on the time at which the aortic extract fractions are added to the lymphoid cultures. This effect of aortic extracts does not result principally from protease inhibitors known to be present in these fractions, since removal of these molecules does not abrogate the inhibiting effects on mitogenic reactivity. Intraperitoneal administration to mice of the aortic low MW fraction substantially reduces primary and secondary humoral immune response to SRBC.