Histochemical localisation of acid phosphatase and non-specific esterase in the midguts of two species of tick, Boophilus microplus and Rhipicephalus appendiculatus, as determined by light microscopy.

Serial sections of glycol methacrylate-embedded and frozen midguts of Boophilus microplus and Rhipicephalus appendiculatus were studied histochemically by light microscopy. The use of the naphthol AS-TR phosphate technique combined with glycol methacrylate embedding enabled the precise localisation of lysosomal enzyme activity, despite the ubiquity of haematin granules in tick midgut epithelia. The presence of acid phosphatase and non-specific esterase activity in the same cells was observed in all of the various developmental stages and feeding phases of the ticks. The pattern of appearance of these cells paralleled the reported level of protease activity in the midgut lumen. The cells were found to be solitary, particularly during the slow digestive phases, and appeared to move into the lumen, where they eventually disintegrated. The cells therefore appear to function as holocrine secretory cells. This is the first report indicating the presence of such secretory cells in the midgut of unfed ticks. The disintegration of these cells in the lumen suggests that lumenal digestion may be more important than hitherto realised.