Age-related changes in localization of injected radiolabelled lymphocytes in the lymph nodes of antigen-stimulated mice.

The localization of i.v. injected syngeneic lymph node cells, radiolabelled with 51Cr or 75Se-L-selenomethionine, was studied in male CBA/H mice aged between 3 and 30 months. The following results were obtained. (1) Localization of cells from young adult donors was greater in the s.c. lymph nodes of old than of young recipients, the main increase being between 15 and 17 months of age. Increases in lymph node weight and DNA-synthesis were also seen at this time; but the rise in cell localization was significant even when calculated per unit of tissue weight. Splenic localization either declined slightly with age or, like the liver, showed no significant change. (2) Local antigenic stimulation by a single injection of sheep erythrocytes into one front footpad, 24 hr before lymph node cell injection, resulted in increased localization in the regional lymph nodes of 3-17 month old, but rarely of 24-30 month old mice. (3) No consistent differences in localization were observed between lymph node cells from 4-month and 25-month old donors. Both age-related and antigen-related increases in cell localization were at least partly attributable to an enhanced rate of entry of lymphocytes from the blood to the lymph nodes. Although the changes underlying the decline in antigen-related localization of cells in old recipients have still to be clarified, it is probable that the defective immune responses of old mice result partly from this decline.