Recovery of human basophils after FMLP-stimulated secretion

Background - Basophils are circulating, secretory granulocytes that are generally considered to be end-stage cells. In one species of guinea-pigs, basophilic leucocytes have been shown to recover from stimulated secretion in short-term cultures. Similar studies have not been done using human basophils. Objective - The purpose of this study was to examine human basophils in short-term recovery intervals following stimulation of secretion to determine whether visual evidence of recovery occurred. Methods - We examined the ultrastructural morphology of early recovery (10 min-6 h) of human basophils following secretion stimulated by formyl-methionyl-leucyl-phenylalanine (FMLP). A combined technique for electron microscopy consisted of post-fixation exposure to cationized ferritin and reduced osmium, providing maximum quality images and allowing identification of intracellular spaces/organelles that opened to the cell surface, often out of the plane of section. Results - The ultrastructural evaluation revealed that control basophils (0 time-6 h) did not undergo regulated secretion or develop the morphologies associated with recovery following secretion. FMLP-stimulated basophils underwent an overlapping continuum of piecemeal degranulation → anaphylactic degranulation (0 time-1 min), producing vesicle- and granule-free, completely degranulated, viable, mature basophils with polylobed nuclei. The early recovery period (10 min-6 h) following FMLP stimulation was characterized by reconstitution of granules. Morphological mechanisms for granule reconstitution included a mixture of conservation, condensation, and synthetic events. Conclusion - Human basophils, like guinea pig basophils, have the potential to recover from regulated secretion.