Changes in host muscles induced by excretory/secretory products of larval Trichinella spiralis and Trichinella pseudospiralis.

Excretory/secretory (ES) products obtained by in vitro culture of infective-stage larvae of Trichinella spiralis and T. pseudospiralis were injected intramuscularly at various intervals into mice. Mini-osmotic pumps containing T. spiralis ES products were also implanted subcutaneously and intraperitoneally into rats. The introduction of ES materials into muscles elicited extensive lesions which included dissolution of myofibres, mobilization of mononuclear and polymorphonuclear leucocytes, angiogenesis, hypertrophy of myonuclei, myotube formation, mitosis, muscle bundles becoming rounded and separated from each other, disappearance of Z, I and A bands of sarcomeres, increase in endoplasmic reticulum and Golgi complexes, decrease in glycogen and relocation of mitochondria. These are considered as degenerative/regenerative changes of muscles to injury. Immunodominant epitopes of specific 45-53 kDa glycoproteins in ES antigens of T. spiralis could not be detected in hypertrophic nuclei of injected muscles by using polyclonal and monoclonal antibodies and immunocytochemical methods. ES products of T. spiralis failed to stimulate unsensitized lymphocytes in the lymphocyte transformation test. Infective-stage larvae of T. spiralis released from muscles were found capable of forming nurse cells after injection subcutaneously into rats. It is postulated that the invasion of muscles by trichinellids elicits two independent events, i.e. a general degenerative/regenerative response of muscles and a specific change in genomic expression of myonuclei. The two events are probably mediated by different effector molecules.