HISTAMINE IMMUNOHISTOCHEMISTRY IS SUPERIOR TO THE CONVENTIONAL HEPARIN-BASED ROUTINE STAINING METHODOLOGY FOR INVESTIGATIONS OF HUMAN SKIN MAST-CELLS

Conventional studies of mast cells are limited by methodological restr ictions such as a selective fixative-dependent routine staining blocka ge. This is thought to depend on the biochemical differences of the ma st cell granule contents suggesting a cellular heterogeneity. Investig ations of human mast cells, using routine methods, also suffer from th e problem of a low signal-to-noise ratio. In the present study, normal human skin was used to compare an immunohistochemical method for hist amine with two recommended mast-cell fixatives and a new commercial fi xative in combination with three routine stains. Mast cells were found throughout the dermis with all the routine stains used. However, immu nohistochemistry gave profoundly better results. Small structures, suc h as thin cytoplasmatic extensions and single granules, were readily d etectable. Double-staining (immunohistochemistry followed by routine s taining) revealed differences in staining capacity. All immunoreactive cells were not stained by routine stains and sometimes the opposite w as also seen. This supports earlier reported evidence of heterogeneity , not only between skin and intestinal mast cells but also among skin mast cells themselves. Furthermore, by focusing on histamine, instead of heparin, we probably overcame the problems of the selective fixativ e-dependent routine staining blockage. Finally, the immunofluorescence technique provides a high signal-to-noise ratio and is an excellent m ethod for making high-quality microphotographs of human mast cells. In conclusion, we have found histamine immunohistochemistry (a) to be ea sy to perform, (b) to show cytoplasmic details better of the, sometime s, dendritic-type mast cells, (c) to result in a higher signal-to-nois e ratio, i.e. a better detectability, resulting in a higher number of cells being evident, and (d) to reveal the presence of histamine, inst ead of heparin, thus being more relevant to all kinds of histamine-rel ated scientific endeavours. However, routine methods occasionally reve aled single cells not visualized by the histamine immunohistochemistry .