Purified human neutrophils from 48 individuals were tested for their capacity to kill antibody-coated target cells in vitro in the absence or presence of stimulating agents. The agents used to stimulate cytotoxic capacity were the monoclonal antibody (MAb) WEM-G1, colony- stimulating factor (CSF-alpha), or mononuclear cell supernatant (MNC- SN). There existed an heterogeneity among the neutrophils of different individuals in the capacity to kill target cells both in the unstimulated (“resting”) or the stimulated state. A positive correlation was found between the ability of neutrophils to kill in the “resting” state and their capacity to be stimulated by MAb WEM-G1, CSF- alpha, or MNC-SN. Furthermore, a strong positive correlation in the ability of neutrophils to be stimulated by the MAb WEM-G1 and either CSF-alpha (r = .76) or MNC-SN (r = .68), as well as between CSF-alpha and MNC-SN (r = .79) was demonstrated. No correlation was seen, however, between stimulation of neutrophil function in vitro and total blood leukocyte counts, neutrophil counts, monocyte counts, or intensity of binding of MAb WEM-G1. The observation that neutrophils respond to a similar extent to different types of stimulators, -such as cytokines (CSF-alpha and MNC-SN) and MAb, suggests that these two factors may be operating through a common mechanism and the degree of stimulation may reflect an intrinsic responsiveness of neutrophils that differs among individuals. Our results also suggest a potential clinical use of WEM-G1 in measuring neutrophil functional capacity in vitro and predicting the capacity to respond to CSF-like cytokines.

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