A reappraisal on the modes of cell death in pilomatricoma

The modes of cell death in pilomatricoma were analysed using 27 nodules. The shadow cells with lost nuclei and preserved cytoplasms were morphologically considered to be derived from basaloid cells via transitional cells, which showed gradual loss of nucleic acid by Feulgen reaction and methylgreen‐pyronin stain and no nuclear fragmentation. This process was regarded as cell death associated with terminal differentiation into hair. Amorphous debris among the shadow cells contained many fragmented nuclei (apoptotic bodies), which were directly derived from basaloid cell layer focally undergoing apoptosis and did not have any transition to transitional cells. Although in situ 3′‐tailing reaction for a detection of dying cells labelled both transitional cells and apoptotic bodies in the amorphous debris, these two components were considered to be on different histogenetic pathways. Immunostainings for the Bcl‐2 family revealed no expression of Bax, Bad or Bak protein in any components, whereas Bcl‐2 protein was detected in the periphery of basaloid cell layer, but not in the transitional or shadow cells. These results indicate that there are two different modes of cell death in pilomatricoma: i) terminal differentiation into shadow cells; and ii) conventional apoptosis observed as amorphous debris.