Genetic immunisation with bovine beta-lactoglobulin cDNA induces a preventive and persistent inhibition of specific anti-BLG IgE response in mice.

BACKGROUND Various studies have shown that DNA immunisation with gene allergen induces a non-allergic response. METHODS We applied this new type of vaccination to bovine beta-lactoglobulin (BLG), a major cow's milk allergen, using a plasmid that allows the production of a partially secreted protein. Specific antibodies and cytokines were quantified in different immunisation protocols. RESULTS The primary response in mice immunised with BLG-encoding plasmid (pBLG) is of the Th1 type. Restricted recognition of a native form of BLG in pBLG mice contrasted with a broader range of recognition in BLG-in-alum-immunised mice, notwithstanding the fact that alum favours the presentation of a native form of the antigen. We also demonstrated an inhibitory effect of pDNA immunisation on the Th2 response induced by a subsequent immunisation using BLG adsorbed on alum. However, this preventive effect is highly dependent on the time of pre-administration of the pBLG, with an optimal effect when pDNA immunisation occurred at least 21 days before protein administration. This preventive effect resulted concomitantly in the inhibition of BLG-specific IgE, in the induction of specific IgG2a, and in the decrease of the specific IgG1/IgG2 ratio. It is accompanied by an increase in IFNgamma and IL-10 secretion. Moreover, the preventive effect was shown to be persistent even after a booster immunisation with alum-adsorbed BLG. The Th1 orientation of the response is very likely due to the presentation of the protein in the Th1 environment due to plasmid immunostimulatory sequences, as intramuscular injection of BLG itself leads to a weak Th2 response and had no preventive effect on a subsequent sensitisation. CONCLUSION This study further demonstrates the potential use of DNA immunisation for prevention of IgE response, but the window of action seems to be very restricted if we are to inhibit an established Th2 response efficiently.