The influence of lipofectin on the in vitro stimulation of murine spleen cells by bacterial DNA and plasmid DNA vectors.

Lipofectin is a mixture of two cationic lipids, N-[1-(2,3-dioleyloxy)propyl]-n,n,n-trimethylammonium chloride (DOTMA) and dioleoyl phosphotidylethanolamine (DOPE), and has been commonly used to promote transfection of plasmid vectors in vitro and in vivo. In these experiments, the effect of lipofectin on in vitro immunostimulation by bacterial and plasmid DNA was tested to determine if these lipids can also influence immune properties of DNA. As a model, spleen cells from BALB/c and C3H/HeJ mice were cultured with DNA from either Escherichia coli DNA or the pEGFP-N1 plasmid at various ratios with lipofectin. As an index of immune stimulation, in vitro proliferation as well as production of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) were assessed. For both bacterial DNA and plasmid DNA, the presence of lipofectin led to a marked increase in the production of IFN-gamma under conditions in which increases in IL-12 production were limited. The IFN-gamma production was nevertheless dependent on IL-12, as shown by the effects of anti-IL-12 antibodies. Under these culture conditions, lipofectin did not significantly augment proliferation induced by DNA. These findings indicate that lipofectin can increase the in vitro immunostimulatory effects of bacterial and plasmid DNA, although the magnitude of the increase may vary among responses.