Functional assessment of cellular non-specific and specific immunity in selected healthy elderly

The immune system in the elderly: III. Innate immunity

The capability to cope with infectious agents and cancer cells resides not only in adaptive immune responses against specific antigens, mediated by T and B lymphocytes clonally distributed, but also in natural immune reactions. These innate defence mechanisms include chemotaxis, phagocytosis, natural cytotoxicity, cell interactions, and soluble mediators or cytokines. However, specific and natural immune mechanisms are always closely linked and interconnected, providing the primary defense against pathogens. The Authors discuss the main changes observed with advancing age in granulocytes and natural killer (NK) cell activity, in the expression and function of adhesion molecules, and in the pattern of cytokine production. Since phagocytic function is the primary mechanism through which the immune system eliminates most extracellular pathogenic microorganisms, analysis of this function is of clinical importance. Neutrophils from aged subjects often exhibit a diminished phagocytic capacity, as well as a depressed respiratory burst, notwithstanding an activated state. The activity of NK cells during aging has been studied extensively and different results have been reported. The most consistent data indicate an increase in cells with high NK activity with advancing age. Cells from healthy centenarians can efficiently kill target cells. This finding seems to suggest that innate immunity and in particular NK cell activity, is not heavily deteriorated with age. Conversely, a low NK activity is a predictor of impending morbidity. Immunosenescence is associated with increased expression of several cell adhesion molecules (CAM) resulting in an augmented capacity to adhere. Finally, also the cytokine network, responsible for differentiation, proliferation, and survival of lymphoid cells, undergoes complex changes with age. The main findings are a Th1 to Th2 cytokine production shift and an increased production of proinflammatory cytokines, which could explain many aspects of age-associated pathological events, such as atherosclerosis and osteoporosis.

Age-associated differences in neutrophil oxidative burst (chemiluminescence)

Phagocytic defensive functions consist of a sequence of events, including migration, phagocytosis, secretion, and the release of reactive oxygen species (ROS). The last of these (also called "oxidative burst") has not received due attention in the elderly, even though it can be considered the most important event in the process of killing an invading microorganism. The aim of the present study was to investigate the oxidative burst activity of polymorphonuclear neutrophil leukocytes (PMNs) in relation to age, using a technique that specifically identifies ROS production: luminol-amplified chemiluminescence (LACL). Besides the use of LACL, a particular feature of the study was the use of five rather than just one or two different stimulants: two particulate (Candida albicans and zymosan) and three soluble ones [N-formyl-methionyl-leucyl-phenylalanine (fMLP), phorbol 12 myristate 13 acetate (PMA), and polyanetholesulfonate (liquoid)]. This approach allowed us to observe a dichotomy between the effects of Candida and zymosan (particulates), which were not significantly different in the elderly subjects compared to the young controls, and those of fMLP, PMA, and liquoid (solubles), which showed a significant reduction in LACL in the elderly group. Considering the different results obtained with the various stimulants adopted that are all believed to have NADPH oxidase as a common final target of oxidative burst, it may be postulated that aging can influence the different transductional pathways in different ways.

Effects of different levels of dietary zinc on the gilthead, Sparus aurata during the growing season

Gilthead were fed three diets. Diet A was the control diet, whereas diets B and C were supplemented with 300 and 900 mg Zn/kg, respectively. Fish fed with diet C, at the end of the experiment, showed the lowest weight. Zinc concentrations presented the higher values in gills, liver, and kidney. Muscle and brain had the lower mean values and showed a tight control of zinc levels. These results reinforce the hypothesis that zinc in the CNS should be strictly controlled in order to maintain the functional role of the metal. Significant differences in tissue zinc concentrations were obtained between fish fed different amounts of zinc, the metal concentrations being higher in tissues of fish fed diet C. The tissue decrease of zinc, found at the end of the experiment, may depend on a lower feed consumption or on different zinc requirements during the cold season. These changes, even if not univocal among the three diets, may be associated with the life cycle of fish. Furthermore, copper concentrations were little affected by the different concentrations of zinc in the three diets; liver and kidney presented the highest concentrations; liver showed a significant decrease in copper content at the end of the experiment. We conclude that: zinc concentrations of the diet may affect the gilthead weights and the tissual metal content; and zinc concentrations in the diets, depending on the growth rate, may be varied depending on the season.

Increased chemiluminescence response of neutrophils from the peripheral blood of patients with senile dementia of the Alzheimer's type

The metabolic activity of circulating neutrophils from patients with senile dementia of the Alzheimer's type (SDAT) was investigated by a chemiluminescence assay and compared with that of old and young healthy controls. Neutrophils from demented patients showed a higher and faster chemiluminescence emission than those of controls when activated in vitro by autologous or heterologous sera. Granulocytes from patients with Parkinson's disease did not show an increased chemiluminescence activity. Moreover, serum from patients with SDAT depressed the chemiluminescence emission of granulocytes from young donors. Serum levels of alpha 1-antichymotrypsin (alpha 1-ACT) were also determined and were found to be higher in demented subjects than in old and young controls. These data suggest that peripheral and systemic indexes of inflammation are present in the disease and might be associated with mental deterioration.