Age-Related Alterations in Actin Cytoskeleton and Receptor Expression in Human Leukocytes

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Abstract
We studied a number of parameters, which may all depend upon cytoskeletal function, comparing lymphocytes and granulocytes (PMN)from young and old healthy donors. F-actin content was measured by NBD-phallacidin staining, followed by flow cytometry and was expressed as mean channel fluorescence (MCF). There were no differences in the basal F-actin content of PMN obtained from young (under 35 years old) and old donors (above 65 years). In contrast, the basal F-actin content was higher in lymphocytes obtained from the old donors (MCF, 56.8 ± 2.9 vs 48.1 ±2.6 in the young; mean ± SEM, n = 20, p < .03). Stimulus-induced actin polymerization was slightly lower in the older age-group both in PMN and lymphocytes, but a significant difference was found only in PMN stimulated with the chemotactic peptide, n-formyl-methionyl-leucyl-phenylalanine (MCF 97.9 ± 4.7 vs 88.6 ± 3.4;young vs old, mean ± SEM, n = 20, p < .05). Interleukin-2 receptor expression was measured by staining with FITC-conjugated anti-CD25 antibodies and flow cytometry, following stimulation with phytohemagglutinin (PHA) or pokeweed mitogen (PWM). Perturbation of the cytoskeletal system with pentoxifylline, which has been shown to decrease F-actin content and inhibit the expression of several cell surface receptors, had similar effects on leukocytes from young and old donors. The expression of the chemotactic peptide receptors in PMN was lower in the older group compared to the young (MCF 34 ± 2 vs 39 ± 2; mean ± SEM, n = 20, p < .03); however, no differences were found in basal and stimulated complement receptor 3 (CR3) expression. We conclude that the state of actin and its function are altered in granulocytes and lymphocytes obtained from healthy elderly, and in view of the ubiquitous presence of actin and its role in a variety of biological processes, changes in actin physiology may be an important aspect of aging

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