Human mast cells synthesize new granules during recovery from degranulation. In vitro studies with mast cells purified from human lungs

Secretory cells undergoing release and recovery events related to constitutive and/or stimulus-initiated secretion might be expected to undergo distinctive changes in morphology as well. We studied the release and recovery events of human mast cell secretion stimulated by antibody to immunoglobulin E. We used enzymatically digested mast cells from human lung specimens further purified by countercurrent centrifugation elutriation. Release kinetics were like those reported for isolated human lung mast cells. In two complete kinetic experiments we restudied these early release patterns (0 to 30 minutes). Mast cells, either stimulated or controls, were then cultured and sampled for electronmicroscopic studies at periodic intervals (3 to 48 hours). We describe events of the late recovery period here, although some overlap with processes seen in early recovery samples occurred. Mast cells that released nearly all their cytoplasmic granules and exteriorized the containers, eg, granule-channel membranes, underwent progressive enlargement of Golgi structures and development of numerous small cytoplasmic vesicles and small, membrane-bound granules filled with particulate and dense content. Ultimately, new mature cytoplasmic granules of all substructural patterns occurred. Nuclear blast changes and expansion of cytoplasmic mass accompanied this period of new granule synthesis. Mixed recovery patterns were present in individual cells. These represented the morphological expression of a variety of recovery events. Thus, some cells showed a combination of channel recovery and remodeling to form new granule containers within which condensation of content produced crystalline patterns, as well as synthesis of new granules, as described here. This morphological versatility resulted in multiple mast cell morphological phenotypes during these release and recovery processes.