F-Met peptide-induced degranulation of human basophils

We examined the kinetics of morphologic change induced by stimulation of human basophils with f-Met peptide using partially purified cells from normal donors. Supernatants were collected at 30 and 60 minutes and assayed for histamine with an automated fluorometric technique. Samples of basophils were prepared for electron microscopy at 0, 10, 20, 30 seconds and 1, 2, 5 and 10 minutes poststimulation with f-Met peptide. We found that f-Met peptide, a bacterial peptide, induced a unique sequence of morphologic events that included morphologies we have previously identified and termed piecemeal degranulation in human basophils in situ as well as those induced by IgE mechanisms ex vivo and termed anaphylactic degranulation, thus supporting a general degranulation model for basophils and mast cells (Dvorak HF, Dvorak AM: In Clinics of Haematology, Granulocyte and Monocyte Abnormalities, Vol 4, edited by Lichtman MA, p 651. London, WB Saunders Co, Ltd, 1975). In addition to this degranulation continuum, we found that chambers of releasing granules underwent extraordinary increases in size as they emptied their contents and before their resolution by extrusion. The enlarging granule chambers accumulated numerous concentric dense membranes, vesicles, and Charcot-Leyden crystals. These early changes generally preceded 1/2 -maximum histamine release, whereas the latter extrusion of full granules, emptied granules and their membranous contents coincided with 1/2 -maximum histamine release (Warner JA, Peters SP, Lichtenstein LM, Hubbard W, Yancey KB, Stevenson HC, Miller PJ, MacGlashan DW Jr. J Leukocyte Biol 45:558, 1989). Shedding of membranes from several sources accompanied extrusion of granules and intragranular Charcot-Leyden crystals. These sources included the expanded granule membranes from empty granules, granule membranes from full granules, collections of intragranular concentric dense membranes and vesicles, and surface membranes and processes. These extraordinary membrane shifts were generated and persisted over the 10-minute period examined and coincided with the later time frame within which leukotriene C₄ was generated and released from human basophils stimulated by f-Met peptide (Warner JA, Peters SP, Lichtenstein LM, Hubbard W, Yancey KB, Stevenson HC, Miller PJ, MacGlashan DW Jr: J Leukocyte Biol 45:558, 1989). Viable basophils, completely free of both full and empty granules, showed some morphologic evidence of recovery of granule products by 10 minutes after stimulation with f-Met peptide. The unique morphology of f-Met peptide-induced degranulation of human basophils is supported by the uniqueness of the biochemical events associated with this trigger. The early phase of this anatomic continuum may reflect relevant in situ activity of basophils, since we regularly find piecemeal degranulation in tissue basophils in human disease. Although precise triggers for piecemeal degranulation are not yet known, this bacterial product may be one of many bacterial, viral, or cellular products with the capability for the induction of piecemeal degranulation.