Histamine-releasing factor (HRF) is a cytokine produced by mononuclear leukocytes when stimulated with antigens or mitogens. HRF is capable of inducing degranulation of basophils and release of histamine. To determine if respiratory viruses can induce HRF production, mononuclear leukocytes from healthy adult donors were exposed to influenza or respiratory syncytial virus in vitro. HRF activity was tested by culturing the supernatants with fresh peripheral blood leukocytes and measuring the percentage of histamine released. Significant enhancement in histamine release was found in both virus groups compared with that of media controls. Thus, mononuclear leukocytes from normal individuals produce HRF in response to exposure to respiratory viruses, suggesting that this cytokine, which causes basophil degranulation, may play a role in the mechanism of virus-induced bronchospasm.
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