Differential staining of mast cells with toluidine blue.

Mast cells play a significant role in inflammatory diseases such as asthma, inflammatory bowel disease, and autoimmune diseases. Inhibition of c-kit receptor tyrosine kinase, a growth factor receptor, significantly reduces mast cell numbers. The purpose of this study was to determine the effect of Compound X (a c-kit inhibitor) on mast cell numbers in rats. Connective tissue mast cells (CTMCs) and mucosal mast cells (MMCs) have differing histochemical characteristics which presents a challenge when staining for quantification by semi-automated image analysis. CTMCs are present in tissues such as tongue and skin and will stain readily in tissues fixed routinely. In contrast, MMCs, such as those present in the intestinal mucosa, are sensitive to fixation. Brief fixation in Carnoy's solution, although seldom used due to its composition (a mixture of ethanol, chloroform, and acetic acid), was employed to fix tissues for MMC staining, while tissues for CTMC demonstration were fixed in 10% neutral buffered formalin. An enzyme histochemistry method, napthol AS-D choloroacetate (specific esterase), was briefly considered for staining; however, granulocytes stained along with mast cells, requiring manual identification and exclusion, thereby rendering the method incompatible with automated means of quantification. Instead, staining was performed using two different toluidine blue methods which have proven conducive to semi-automated image analysis techniques. CTMCs were stained using Luna's toluidine blue, while MMCs were stained with Matsson's toluidine blue modification. In summary, the selected methods, based upon a conventional stain, were easy to do and successfully identified both populations of mast cells for quantification by image analysis. [ABSTRACT FROM AUTHOR]