46 Journal of Leukocyte Biology Volume 51, January 1992 Inhibition of neutrophil chemotaxis and chemokinesis associated with a plasma protein in aging rats: selective depression of cell responses mediated by complement-derived chemoattractants S. B. V. Mello,1 S. H. P. Farsky,* P. Sannomiya,* and J. GarciaLeme* Department of Pharmacology, Institute of Biomedical Sciences, and Laboratory of Clinical Investigation, t School of Medicine, University of S#{227}oPaulo, S#{227}oPaulo, Brazil Abstract: The influence of aging on neutrophil chemo- taxis, chemokinesis, and superoxide production was in- vestigated in rats. Animals of two age groups, 3 to 4 months and 20 to 21 months, were used. Equivalent neu- trophil chemotactic responses to N-formyl-methionyl- leucyl-phenylalanine (fMLP), leukotriene B4 (LTB4), and bacterial lipopolysaccharide (LPS)-activated plasma were observed in both groups of animals, with cells suspended in Hanks’ balanced salt solution (HBSS). However, cross- incubation studies in which cells from young adult rats were exposed to plasma from aged donors, then resus- pended in HBSS for testing, showed marked changes in the ability of the cells to respond to the chemoattractants. The response to LPS-activated plasma was reduced, whereas responses to fMLP and LTB4 remained un- altered. Previous incubation of the cells with homologous plasma from young donors produced no effect. The in- hibitory activity developing with advancing age affected not only chemotaxis but also random movement stimu- lated by LPS-activated plasma. The inhibitory activity of chemotaxis and chemokinesis in plasma of aged animals was heat labile (56#{176}C), vanished in the presence of a pro- teolytic enzyme like trypsin, and was maintained after dialysis with 12,00OMr retention dialysis tubing. The material did not influence superoxide production by stimulated neutrophils. It is suggested that inhibition of neutrophil locomotion with advancing age is associated with a plasma protein capable of interacting with neutro- phil receptors for complement-derived chemoattractants. The inhibitory substance might influence neutrophil re- sponses to infection and inflammation in the elderly. J. Leukoc. Biol. 51: 46-52; 1992. Key Words: aging - chemotaxis chemokinesis . superoxide pro- duction INTRODUCTION Comparatively few studies have been carried out on host de- fenses in an aged population. However, the clinical evidence is persuasive that elderly individuals have great susceptibility to and morbidity and mortality from bacterial infectious agents [8, 9, 22]. In many instances, the heterogeneity of assay results renders it difficult to assign a cause for any in vivo impaired response to bacterial pathogens associated with aging [29]. Notwithstanding this, it is widely accepted that with advancing age there is a progressive decrement in cellular functions that are relevant for host defense against infection. Aging is accompanied by significant changes in the immune response [10, 18, 35, 36, 44, 48]. Human peripheral granulocytes from elderly subjects are reported to exhibit defects in chemotaxis [23, 30]. Peritoneal macrophages from aged rats produce or secrete less interleukin 1 and tumor necrosis factor [3]. In addition, defects in nonspecific responses, such as fever, are described in the elderly [4]. Despite the fact that polymorphonuclear leukocytes play a major role in primary host defense against infection, obser- vations currently available provide only a partial basis for the understanding of age-related changes in the function of these cells. The present work was, therefore, undertaken to inves- tigate the influence of aging on neutrophil function in the rat. The data to be presented suggest that inhibition of chemotaxis and chemokinesis occurs with advancing age, that the inhibition is restricted to cell responses mediated by complement-derived chemotactic agents, that it is associated with the presence of an inhibitory protein in plasma of these animals, and that superoxide generation is not affected. MATERIAL AND METHODS Animals Male Wistar rats aged 3 to 4 months and weighing 250 to 300 g, or aged 20 to 21 months and weighing 450 to 500 g, were used. The animals were allowed a standard diet and water ad libitum. Neutrophil Isolation With a single exception in which aged animals were used as cell donors, neutrophils were obtained from young adult rats 4 h after the intraperitoneal injection of 20 ml of 1% oyster glycogen (type II, Sigma) in phosphate-buffered saline (PBS). The animals were anesthetized with ether and the cells col- lected by rinsing the abdominal cavity with Hanks’ balanced salt solution (HBSS) containing 1 U/mi heparin. Cell viabil- ity was confirmed by the trypan blue exclusion method. Abbreviations: DMSO, dimethyl sulfoxide, fMLP, N-formyl-methionyl- leucyl-phenylalanine; HBSS, Hanks’ balanced salt solution; LPS, lipopoly- saccharide; LTB4, leukotriene B4; PBS, phosphate-buffered saline; PMA, phorbol myristate acetate; SOD, superoxide dismutase. Reprint requests: J. Garcia-Leme, Department of Pharmacology, Insti- tute of Biomedical Sciences, University of S#{227}o Paulo, 05508 S#{227}o Paulo, SP, Brazil. Received January 25, 1991; accepted April 18, 1991.