[Role of neutrophil and T cell functions in host defense mechanisms of the elderly]

We studied neutrophil functions (phagocytosis, intracellular killing and chemotaxis with or without recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) and T cell functions (lymphocyte proliferation and production of GM-CSF in response to phytohemagglutin (PHA)) to clarify host defense mechanisms in the elderly. There was no significant difference in phagocytic activity of neutrophils between the elderly and control young adults. rhGM-CSF enhanced phagocytosis by neutrophils, and a similar degree of enhancement was obtained in both groups. Killing activity of neutrophils evaluated by the new Nitroblue tetrazolium reduction test in the elderly was significantly lower than that in young adults (p < 0.001), however, pretreatment of neutrophils with rhGM-CSF resulted in an increase of killing activity in the elderly, raising their response to a level comparable to that of young adults pretreated with rhGM-CSF. There was no significant difference between the elderly and young adults in chemotaxis of neutrophils. rhGM-CSF alone did not prime chemotaxis, but primed chemotaxis in response to chemoattractant (N-formyl-methionyl-leucyl-phenylalanin) in both individuals. Lymphocyte proliferation and production of GM-CSF in response to PHA in the elderly were significantly lower than those in the young adults (p < 0.001, p < 0.05, respectively). These results indicated that impaired T cell functions may contribute, at least in part, to susceptibility to bacterial infection in the elderly.