Neutrophil granulocyte functions in the elderly

Abstract

The immune response weakens during aging. Especially, the altered functions of the lymphocytes of the adaptive immune system have been extensively studied. Aged persons > 65 years display a predisposition to inflammation and infection combined with an increase in morbidity and mortality than younger individuals. In the past few years it has been discovered that certain functions of the innate immune system, which build the first line of defense against pathogenic microorganisms, are altered with aging. Among the cells of the innate immune system, neutrophilic granulocytes (polymorphonuclear leukocytes, PMN, neutrophils) eliminate invaded bacteria and fungi and play an accepted important role in regulation of the immune response. In vitro studies demonstrate that neutrophilic functions such as phagocytosis, generation of reactive oxygen species (ROS), intracellular killing, degranulation, and possibly chemotaxis are changed in elderly persons whereas the number of circulating neutrophils are unaltered compared to young persons. However, the reported data of different investigators regarding the above-mentioned functions are sometimes controversial. This may result from the use of different isolation methods of neutrophils, the degree of contaminating cells and preactivation of neutrophils during isolation. It could be shown that most of the adhesion surface molecules and receptors of neutrophils are not impaired in function and expression with age. But there is increasing evidence that age-related changes affect receptor-dependent signal transduction and membrane content and fluidity, which in turn lead to a decline in function and in inhibition of apoptosis. Further research has to be done to identify the molecular mechanisms that are responsible for the age-related modulations in human neutrophils.