[The role of G-CSF in host defense mechanisms of the elderly].

It has been generally agreed that the elderly had a greater susceptibility, morbidity, and mortality in regard to a variety of bacterial infections. To clarify the host defence mechanism in the elderly, we studied the effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on neutrophil functions, the production of G-CSF by peripheral blood monocytes in response to lipopolysaccharide (LPS) and the serum levels of G-CSF in patients with bacterial pneumonia. There was no significant difference in the phagocytic activity of neutrophils between the elderly and control young adults. rhG-CSF enhanced phagocytosis by neutrophils, and a similar degree of enhancement was obtained in both group. Killing activity of neutrophils assessed by the new nitroblue tetrazolium reduction test in the elderly was significantly lower than that in young adults (p < 0.001), however, pretreatment with rhG-CSF resulted in an increase of killing activity in the elderly, raising their response to a level compatible to that of young adults pretreated with rhG-CSF. The amount of G-CSF in the culture supernatants from LPS-stimulated peripheral blood monocytes of the elderly was significantly lower than that of young adults (p < 0.05). The serum levels of G-CSF in the acute phase of bacterial pneumonia in the elderly were significantly lower than those of young adults (p < 0.01). These results indicated that impaired monocyte function may contribute, at least in part, to susceptibility to bacterial infection in the elderly.