Histamine-releasing activity (HRA). III. HRA induced human basophil histamine release by provoking noncytotoxic granule exocytosis

Histamine-releasing activity (HRA) is an similar to 10,000-15,000 dalton, protease-sensitive factor that induces the rapid liberation of histamine from human basophils. Production of HRA by human peripheral blood mononuclear cells in vitro is augmented by concanavalin A or antigen, suggesting a mechanism whereby lymphocytes may regulate basophil mediator release in vivo. In order to determine whether HRA provokes conventional exocytosis of basophil granules or, alternatively, results in mediator release by some other mechanism such as vesicular transport or cytotoxicity, the authors investigated the ultrastructural features of human blood basophils purified over Percoll and exposed to HRA in vitro. Those basophils exposed to HRA that did not exhibit evidence of degranulation displayed a single elongated cellular process. The development of this polarized cellular configuration, similar in some respects to that of uropod-bearing motile guinea pig basophils, may have reflected chemokinetic or chemotactic effects of preparations containing HRA activity.