Different response of satellite cells in the kinetics of myogenic regulatory factors and ultrastructural pathology after Trichinella spiralis and T-pseudospiralis infection

Infection of an intracellular parasitic nematode, Trichinella spiralis, res ulted in severe damage in muscle cells which was followed by activation and proliferation of satellite cells. The repairing process, shortly after the damage, histopathologically resembled those seen after mechanical injury. Resemblance was also true for kinetics of expression of myogenic regulatory factors (MyoD, myogenin and MRF4). The difference resided in the next step where the muscle cell infected with T. spiralis transformed to a unique ce ll which is parasitologically known as the nurse cell, and the proliferated satellite cells did not differentiate to the muscle cell but to the nurse cell (misdifferentiation). Thus the nurse cell was a fusion of the transfor med infected muscle cell and misdifferentiated satellite cells. Infection w ith another species of Trichinella, T. pseudospiralis, also caused cell dam age, but more extensively involving the entire length of the infected muscl e cells because no septum was formed to minimize the affected area. Therefo re, a large number of satellite cells were activated and proliferated. The myogenic regulatory factors such as MyoD and myogenin were activated for a longer period than in the case with T. spiralis infection. The infected mus cle cell transformed to the nurse cell, whose cytoplasm was characterized b y extensive smooth endoplasmic reticulum. Satellite cells misdifferentiated to the nurse cell, whose cytoplasm was amorphous, void of distinct cell or ganelles. The two kinds of cytoplasm did not fuse as examined thus far. Thu s infection with T. spiralis and T. pseudospiralis caused misdifferentiatio n of satellite cells, but in a different way.