Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 50, Issue 6 B368-B377, Copyright © 1995 by The Gerontological Society of America
Diminished cell-cell binding by lymphocytes from healthy, elderly humans: evidence for altered activation of LFA-1 function with age
DR Jackola and HM Hallgren
Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, USA.
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.
