Myositis Induced by Naked DNA Immunization with the Gene for Histidyl-tRNA Synthetase

Abstract

Polymyositis is regarded as an autoimmune inflammatory muscle disease. A major subgroup of patients have autoantibodies to cellular histidyl-transfer RNA synthetase (HRS). We have analyzed the role of the autoantigen HRS in the induction of murine myositis in a comparative study of inoculation of BALB/c mice with recombinant HRS protein versus naked DNA coding for HRS. Adult BALB/c mice produced antibodies to human HRS following inoculation with HRS protein and adjuvant, but myositis was not observed. Alternatively, expression plasmid DNA constructs encoding full-length and truncated human HRS were inoculated intramuscularly in gene transfer studies. DNA-inoculated mice produced relatively low anti-HRS antibody titers. However, in contrast to recombinant HRS protein-inoculated mice, HRS gene transfer induced pathology with evidence of cellular infiltration of perivascular and endomysial regions of the inoculated muscle. Multiple inoculations of a plasmid construct encoding a hybrid molecule consisting of HRS and the transferrin receptor cytoplasmic tail induced the highest levels of antibodies and persisting cellular infiltration. Unlike HRS, expression of influenza virus hemagglutinin (HA) following inoculation of an HA plasmid did not induce myositis. Transfer of naked DNA constructs expressing HRS is likely to provide valuable information on the autoimmune response to this protein and its role in the development of myositis. Delivery of naked DNA encoding the gene for the candidate autoantigen histidyl-transfer RNA synthetase (HRS) in polymyositis into skeletal muscle of mice induced a marked inflammatory response that was long-lasting. In contrast, immunization of mice with recombinant HRS protein did not result in myositis. Anti-HRS antibodies were found in mice using both immunization protocols but were of higher titer in mice inoculated with recombinant HRS protein. These differences probably reflect the differences in antigen processing and presentation pathways between endogenous and exogenous delivery of antigens. The expression of autoantigens by naked DNA transfer is a new approach for the development of animal models for autoimmune diseases.