We studied the kinetics of cell-cell adhesion by monocyte-depleted peripheral blood lymphocytes with a stirred-cuvette aggregometer using samples from healthy young (mean age = 25 years) and healthy elderly (mean age = 75 years) human donors. This was a very reproducible assay, as there was virtually no intraindividual variability and very little interindividual variability among donors of the same age group. In all cases, aggregation of cells began immediately upon addition of the protein kinase C activator phorbol myristate acetate (PMA) or the calcium ionophore ionomycin, and continued until reaching an asymptotic limit by 20 minutes or less. Unstimulated cells did not aggregate during this time. The rate of aggregate formation and total amount of aggregation (using young donors' cells) varied between PMA- and ionomycin-stimulated cells, suggesting different mechanisms for initiating cellular aggregation, or possibly, different peripheral blood lymphocyte subsets affected by these activating agents. However, for both stimuli, the rate of aggregation and the total amount of cellular aggregation were significantly lower with the elderly donors' cells. Further, aggregation was Ca2+/Mg2+ dependent, and the reaction required metabolically active cells, as the reaction was inhibited by the addition of sodium azide and 2-deoxy-D-glucose in both donor groups. Pretreating cells with the actin polymerization inhibitor cytochalasin B resulted in 35-40% inhibition of aggregation among young donors' cells, although, interestingly, there was no apparent effect upon the cells capable of forming aggregates in the old donor group. In both donor groups, aggregation by activated cells could be partially blocked by pretreating cells with monoclonal antibodies directed against the alpha and beta chains of the integrin leukocyte function-associated antigen-1 (LFA-1) (CD11a/CD18). These results show that there is diminished cell-cell binding among lymphocytes from healthy, elderly humans, and this is partly due to altered activation of LFA-1 function with age.
Adult Aged