A study of peripheral and central mechanisms of secondary immunodeficiency in atherosclerotic patients demonstrated altered structural layout of lymphocyte membranes due to cholesterol accumulation in the cells. This was associated with increased membrane viscosity, suppressed mitotic activity and lower cap formation rate as well as changed intracellular calcium redistribution. Thymic ischemia due to occlusion or stenosis of thymus-supplying vessels was shown to promote age-related transformation of thymic tissue. Experimental simulation of thymic ischemia resulted in an abrupt drop of serum thymic factor in the blood of animals and the development of an immunodeficient condition.