Phenotypic change of blood‐type eosinophils to tissue‐type eosinophils is induced by various cytokines. We examined the effect of nerve growth factor (NGF) as a candidate for a constitutive cytokine which is able to induce the phenotypic change of eosinophils. The viability of human peripheral blood eosinophils cultured for 4 d was increased from a mean of 26 to a mean of 50 (P 0.001) by the addition of NGF (50 ng/ml). Cytotoxic activity of eosinophils determined by larvicidal activity was increased 2–3‐fold by the addition of NGF (50 ng/ml) (P 0.05). Furthermore, eosinophil chemotactic activity of NGF was demonstrated by the blind well chamber method. Since NGF is produced constitutively from various kinds of cells in local tissues, it is suggested that NGF might be a cytokine responsible for phenotypic change to tissue type eosinophils in conditions without
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