Mast cell TNF mRNA expression in nasal mucosa demonstrated by in situ hybridization: A comparison of mast cell detection methods

We have used S-35-labelled RNA probes to detect TNF cytokine gene expression in nasal mucosa derived from patients with perennial rhinitis. As mast cells comprise a minor component of the total cell population in nasal mucosa, additional methods are needed to determine whether mast cells contribute to the cytokine mRNA detected by in situ hybridization. We have combined in situ hybridization with alternate methods to detect mast cells (tryptase immunostaining or toluidine blue staining) and determined that in situ hybridization coupled with tryptase immunostaining provides optimal methods to detect mast cell cytokine gene expression in tissue sections. Using in situ hybridization and tryptase immunostaining, we demonstrate that mast cells in nasal mucosa can express TNF mRNA. However, the number of tryptase(-), TNF+ cells (1.99 +/- 1.59 cells/mm(2)) exceeded the number of tryptase(+), TNF+ mast cells (0.09 +/- 0.21 cells/mm(2)). Mast cells thus comprised a subpopulation of the total number of TNF mRNA positive cells in nasal mucosa.