Induction of the Mx protein of rainbow trout Oncorhynchus mykiss in vitro and in vivo with poly I:C dsRNA and infectious hematopoietic necrosis virus

Abstract

Expression of the Mx protein of rainbow trout was analyzed after induction by poly I:C dsRNA and infectious hematopoietic necrosis virus (IHNV). Poly I:C dsRNA-treated rainbow trout gonad (RTG-2) cells expressed Mx protein that was detectable by immunoblot analysis at 24 h post induction. Increased expression was observed at 48 h and then declined by 72 h post induction. In contrast, IHNV was not an efficient inducer of Mx protein in cells in culture. An immunocytochemical assay was also established to detect Mx proteins after transient transfection of chinook salmon embryo (CHSE-214) cells with trout Mx cDNA expression clones. Using these same techniques, endogenous Mx protein was detected in RTG-2 cells induced with 5 and 50 μg ml-1 of poly I:C dsRNA at 48 h post induction. In vivo, the appearance of Mx protein in rainbow trout after infection with IHNV (isolated at Rangen Research, Hagerman, ID, USA) was demonstrated in the immunoblots of kidney extracts of 4 out of 4 fish at 2 d post infection. Immunohistochemical staining of the kidney tissue from 3 out of 3 rainbow trout fry infected with the RB-76 strain of IHNV (isolated at Rounded Butte Hatchery, OR, USA) confirmed the production of Mx protein in the kidney tubules at 2 d post infection. These results suggest that Mx is a useful marker for the induction of fish interferon.