Ultrastructural analysis of mast cell recovery after secretion by piecemeal degranulation in B-cell non-Hodgkin's lymphoma.

Mast cells (MC) are critical for a number of pathological conditions, including acute and chronic inflammation and tumor angiogenesis. We have previously demonstrated in B-cell non-Hodgkin's lymphoma (B-NHL) the presence of an heterogeneous population of MC characterized by granules with a morphological semilunar appearance, or piecemeal partial degranulation (PMD), and containing scrolls. With the aim to further elucidate the morphological features of MC in B-NHL, in the present study an ultrastructural analysis of MC recovery after secretion by PMD in B-NHL samples has been carried out. Results indicate that PMD is identified by the presence of partially or completely empty granule containers in the cytoplasm, considered as the morphological endpoint of secretion by PMD. Granule refilling after PMD implies condensation of dense granule matrix material leading to the highly characteristics morphological patterns described in this paper. After the recovery from secretion by PMD in B-NHL, mature MC with full complement of granules displaying crystal, particle, scroll, and mixed patterns are recognizable. We believe that the images presented here, in the absence of MC mitosis, support the possibility that in B-NHL, MC after PMD, refill empty granule containers in situ, as seen in MC during the angiogenic phase of wound-healing, and that both events, PMD and recovery of MC after their degranulation, occur during biological processes in which MC and angiogenesis are strictly interconnected.