Decline of thymus-cell potential in diabetic and aged men

Human peripheral blood thymus lymphocytes are capable of forming, when stimulated by phytohemagglutinin, single-cell-derived colonies in an in vitro soft-agar system. Blood samples were obtained from 33 healthy men ranging in age from 20 to 96 years of age and from 11 diabetic men ranging in age from 42 to 60 years and 11 age-matched controls. With increasing age a reduction in the number of single-cell-derived colonies and a decrease in their residual in vitro proliferation potential was observed. Such a defect appeared at an earlier age in diabetic men. The defect in proliferative potential of cells of either old or diabetic men did not depend on factors present in their blood plasma.