Trichinella spiralis: inhibition of muscle larva growth and development is associated with a delay in expression of infected skeletal muscle characteristics.

Infection of skeletal muscle cells by Trichinella spiralis induces host cells to reenter the cell cycle and these cells subsequently become persistently suspended in apparent G2/M. To investigate the role of the parasite in this process, parasite growth and development within the infected cell was inhibited by irradiation of newborn larvae (48 and 80 krad) prior to infection of host muscle cells. Although larvae entered skeletal muscle cells, irradiation inhibited their subsequent growth and stichosome development, including development of alpha and beta stichocytes. A distinct delay in cell cycle reentry was demonstrated for irradiated larva-infected muscle cells, indicating an interaction between parasite and host factors affecting this host process. Despite effects on stichosome development and this delay, infected muscle cells reentered the cell cycle, expressed increased levels of acid phosphatase, were inhibited in myosin heavy-chain expression, and developed collagen capsules. The results indicate that normal alpha and beta stichocyte development is not required for inducing the infected cell characteristics studied. The model system may be useful in analysis of parasite products that are candidates for regulating various aspects of the infected cell phenotype.