Evaluation of antisense inhibition in a B cell model

An in vitro model has been developed in an attempt to optimise antisense inhibition in B cells as a prelude to transgenic studies. The hypotheses tested were that i) the 3'-untranslated region would be an appropriate target for antisense inhibition; 2) the immunoglobulin heavy chain intronic enhancer could be used to enhance antisense inhibition via increased production of antisense transcripts; and 3) the mouse metallothionein-1 promoter would allow induction of antisense inhibition in B cells. Secreted IgM protein and mRNA were monitored following the stable transfection of a B cell line, HO-2.2, with a series of plasmid constructs containing antisense or sense target sequence DNA under the control of either the mouse metallothionein-1 promoter or homologous (ie same promoter as target sequence) immunoglobulin heavy chain promoter. The 3'-untranslated region proved to be an appropriate target resulting in 70% inhibition of IgM secretion. Compared with untransfected and sense controls, significant decreases in IgM secretion (and RNA levels) were detected in clones transfected with antisense constructs utilising the mouse metallothionein-1 promoter and the immunoglobulin heavy chain intronic enhancer elements. These clones exhibited a further significant reduction in secreted IgM production upon zinc induction. Hybridisation studies demonstrated that decreased protein production was most likely attributable to reduction in RNA levels. In contrast, transfection with antisense constructs had no effect on membrane IgM protein levels which not only confirmed the specificity of antisense action but meant that the B cell remained sensitive to receptor ligation. We conclude that reasonable antisense inhibition of gene product expression can be achieved in B cells by targeting the 3'-untranslated region and using both an inducible promoter (mouse metallothionein-1) and the IgH enhancer to aid antisense RNA production.