Indole reactions of mast cells and enterochromaffin cells related to fixations with and without aldehydes

Summary Survey of a considerable number of rat, mouse and hog tissues which presented large numbers of mast cells in preparations stained with toluidine blue and other metachromatic or basic dyes at low pH levels, revealed numbers of oval bodies of about the same size as mast cells which reacted weakly or even moderately to the postcoupled benzylidene indole reaction. The numbers of these were always less than that of mast cells in toluidine blue sections of the same blocks. They never occurred in clusters of perhaps 15–20 in a single high power field, as mast cells often do. Smooth and especially striated muscle which often formed the background tissue where most mast cells are found with metachromatic stains, regularly present indole reactions due to protein tryptophan. This is usually equal to or stronger than that in the supposed mast cells.Indole reactive bodies whose morphology suggests mast cells are also present in similar numbers in formaldehyde and glutaraldehyde fixed tissue as well as with aldehyde free fixations. Glutaraldehyde and formaldehyde are known to inhibit the benzylidene reaction of 5-HT in vitro (30 min for glutaraldehyde, 3 h for formaldehyde) (Lillie, 1977). This action was avoided in mercury and lead heavy metal fixations and in acetone, Carnoy, chloroform methanol and similar fixations.The mast cell-like bodies are best explained as tangential or oblique sections of individual muscle fibers. We have described the same phenomenon with the ferric ferricyanide (Golodetz-Unna, 1909) reaction (Lillie et al., 1978a), and the PCB reaction is that of tryptophan in these muscle cell sections.In contrast to the DMAB type reaction failure acid diazosafranin successfully demonstrated mast cells with both aldehyde and aldehyde free fixations. This reaction has been shown to occur with 5-HT and 5-HTP (Lillie et al., 1973).