Importance of correlations between phagocytic activity and superoxide production of neutrophils under conditions of voluntary exercise and stress

The importance of the neutrophil function to host defense and tissue damage has been widely recognized. However, the usefulness of the correlation analysis between phagocytic activity and superoxide production of neutrophils is unknown. We investigated the relationship by histochemical NBT assay using rats and mice exposed to voluntary exercises and stresses. The following conclusions were shown from the results in this report and from our previously published findings. The results of voluntary exercise showed significant positive correlations between phagocytic activity and superoxide production of neutrophils after the continuation of the exercise for 8 months, but no relationship after only 3 or 4 months. However, when Salmonella was injected into the same group after 4 months, significant positive correlations were observed immediately following and on the 6th and 14th days after injection. In contrast, negative correlations emerged after psychological stress and severe-crowding stress, suggesting that appropriate expression of neutrophil function was disturbed by the reverse effects, such as by suppression of oxygen-dependent killing capacity or overproduction of toxic free radicals subsequent to these stress. These results suggest that the correlations of phagocytic activity and superoxide production of neutrophils reflect whether a neutrophil functional state is appropriate or not.