Structural diversity of mast cell granules in black and white skin

There are conflicting reports of structural differences between black and white skin, other than pigmentary differences.

To evaluate differences in mast cells between black and white skin.

Biopsies of normal buttock skin were obtained from four African-American males (29.2 +/- 3.0 years old) and four Caucasian males (29.4 +/- 1.2 years old) and processed routinely for electron microscopy. For the quantitative assessment of mast cell granules, five electron micrographs at a final magnification of x 53,700 were analysed for each individual, using a computer-assisted image analyser. More than 10 granules per cell, and a total of 1210 granules, were evaluated for their internal structures.

Mast cells in black skin contained larger granules than those in white skin (P < 0.0001). In black skin, fusion of granules seemed to account for the larger sizes. The percentage of granule matrix occupied by curved lamellae was higher in white skin, whereas parallel-linear striations were more frequent in black skin (P < 0.05). The subgranular distribution of the mast cell proteases, tryptase and cathepsin G, were evaluated by immunoelectron microscopy. Tryptase reactivity was localized preferentially over the parallel-linear striations and partially over the dark amorphous subregions within granules of black skin, whereas it was confined to the peripheral area of granules, including curved lamellae, in white skin. Cathepsin G reactivity was more intense over the electron-dense amorphous areas in both groups, while parallel-linear striations in black skin and curved lamellae in white skin were negative.

This study has confirmed ultrastructural differences in mast cell granules between black and white skin, which may be of functional importance.