Differences and similarities of nurse cells in cysts of Trichinella spiralis and T. pseudospiralis.

The nurse cell in the cyst of Trichinella spiralis comprises at least two kinds of cytoplasm, derived from muscle or satellite cells, as indicated by the pattern of staining using regular dye (haematoxylin and eosin, or toluidine blue), alkaline phosphatase (ALP) expression, acid phosphatase (ACP) expression and immunostaining with an anti-intermediate filament protein (desmin or keratin). Muscle cells undergo basophilic changes following a T. spiralis infection and transform to the nurse cells, accompanied by an increase in ACP activity and the disappearance of desmin. Satellite cells are activated, transformed and joined to the nurse cells but remain eosinophilic. The eosinophilic cytoplasm is accompanied by an increase in desmin and ALP expression but not an increase in ACP activity. Differences in the staining results for ALP or ACP suggest that the two kinds of cytoplasm have different functions. Trichinella pseudospiralis infection results in an increase of ACP activity at a later stage than T. spiralis. There is also a difference in the location pattern of ACP in the cyst of T. spiralis compared with T. pseudospiralis. In T. spiralis, ACP is diffused within the cell, but in T. pseudospiralis, ACP distribution is spotty corresponding to the location of the nucleus. Trichinella pseudospiralis infection is accompanied by a slight increase in ALP activity. Activated satellite cells following a T. pseudospiralis infection exhibit an increase in desmin expression. The present study therefore reveals that nurse cell cytoplasm differs between the two Trichinella species and between the two origins of cytoplasm in the cyst of T. spiralis.