Trichinella spiralis: induction of the basophilic transformation of muscle cells by synchronous newborn larvae.

Newborn larvae (NBL) possess the "transformation potential" (TP) to induce the basophilic transformation of the muscle cell into the nurse cell and to create the nurse cell-muscle larva complex. For investigation as to whether TP is age-dependent, three groups of synchronous NBL (sNBL) were obtained at 1 h, 9 h, and 6 days of age, respectively, and were injected intramuscularly into mice. The TP was demonstrated to be high for both 1- and 9-h-old sNBL, but for 6-day-old sNBL, none was found. The earliest transformation of muscle cells was observed at 48 h postinfection (p.i.) in the first two groups of sNBL. Moreover, for 1-h-old sNBL the numbers of basophilically transformed muscle cells without larvae were 3-fold those of sNBL observed in histology sections. The results indicate that (1) due to the high TP observed in the 1-h-old sNBL group, NBL are born with TP; (2) the TP is lost by aging; and (3) the induction of the basophilic transformation of muscle cells is possible without direct contact between the muscle cell and NBL being required, as contact with released factor(s) alone may be enough.