Human mast cells use conservation and condensation mechanisms during recovery from degranulation. In vitro studies with mast cells purified from human lungs.

Abstract Human lung mast cells were isolated from enzymatically digested lung fragments and partially purified by countercurrent centrifugation elutriation before stimulation with anti-immunoglobulin E (IgE). Stimulated cells and control preparations were fixed for electron microscopy, and replicate samples were obtained for histamine determinations at early times (0 to 20 minutes) after stimulation. Other samples of stimulated and control cells were placed in culture media and recovered for electron microscopic studies after variable times spanning 3 to 48 hours. Two complete kinetic studies of release and recovery were studied. The starting purity of mast cells was 59% and 66% and the maximal histamine release at 20 minutes poststimulus was 72% and 45%, respectively, for these two studies. Mast cells underwent granule swelling and fusion with elongation and enlargement of granule chains to form degranulation channels which permeated the cytoplasm. Granule patterns became swollen and altered within channels which ultimately opened to the exterior through multiple pores. Altered granule matrix disappeared from many open channels. Residual granules that did not participate in this process did not swell and fuse their membranes. Early recovery events included conservation of granule containers (membranes) and contents. Degranulation channels became centrally located and developed granule-shaped domains. Strings of vesicles, lipid bodies, filament-rich cytoplasmic invaginations, and membranes were found at constriction points in resolving channel-granules. As resolution of channel-granules occurred, condensation of channel-granule contents also took place. Progressively dense content developed in granule containers within which focal areas of crystallization and content organization were noted. Eventually, numerous granules with a crystal pattern were found in recovering mast cells. Other granule patterns (scrolls, particles, and mixed) were present but in smaller numbers. Human lung mast cells have the ability to repackage contents in the same container after stimulation with anti-IgE. Although this was a prominent recovery pattern in the earlier periods examined, this did not constitute the only recovery pattern. Overlap with different events at later times was noted. These are currently being further investigated. The biochemical composition and physiologic function(s) of human mast cell granule membranes are unknown. Our findings suggest that certain analogies to other secretory granule membranes may exist. Clearly, containers can be reused, nearly in toto.(ABSTRACT TRUNCATED AT 400 WORDS)