During ultrastructural studies of the early kinetics of anaphylactic degranulation and early and late recovery intervals from these release reactions induced in isolated, partially purified, cultured human lung mast cells stimulated to release histamine and granules by exposure to anti-IgE, we noted the ability of mast cells to undergo morphologic cycles. Following release of most cytoplasmic granules and shedding of large amounts of membranes and cellular processes, small, immature mast cells, nearly devoid of granules, were seen. These lymphocyte-like cells had condensed nuclear chromatin and large nucleoli. Blast transformation of these small cells and expansion of synthetic machinery-laden cytoplasm resulted in large, immature mast cells with small numbers of small, immature progranules and large numbers of lipid bodies in their cytoplasm. This cycle of mast cell morphologic change has considerable similarities to, as well as some differences from, lymphocyte morphologic cycles.
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