Inhibition of immunoglobulin E response to Japanese cedar pollen allergen (Cry j 1) in mice by DNA immunization: different outcomes dependent on the plasmid DNA inoculation method

Summary To develop a new immunotherapy for Japanese cedar (Cryptomeria japonica; CJ) pollinosis, we evaluated the use of DNA immunization by inoculating mice with plasmid DNA encoding Cry j 1 as a CJ pollen major allergen (pCACJ1). Repeated intramuscular (i.m.) inoculation of BALB/c mice with pCACJ1 produced anti‐Cry j 1 antibody responses, which were predominately of the immunoglobulin G2a (IgG2a) type. Furthermore, this inoculation suppressed immunoglobulin E (IgE) and IgG1 antibody responses to subsequent alum‐precipitated Cry j 1 injections. Splenic T cells isolated from mice inoculated with pCACJ1 i.m. secreted interferon‐γ (IFN‐γ), but not interleukin (IL)‐4, in vitro upon stimulation with Cry j 1 as well as with p277–288, a peptide corresponding to the T‐cell epitope of Cry j 1. In contrast, inoculation of BALB/c mice with pCACJ1 by gene gun injection caused response predominantly of the IgG1 type, and enhanced production of anti‐Cry j 1 IgE antibodies to subsequent alum‐precipitated Cry j 1 injections. Splenic T cells isolated from pCACJ1‐innoculated mice by gene gun injection secreted both IFN‐γ and IL‐4 in vitro, upon stimulation with Cry j 1 as well as with p277–288. These findings suggest that i.m. inoculation with pCACJ1 effectively elicits Cry j 1‐specific T helper 1 (Th1)‐type immune responses, resulting in inhibition of the IgE response to Cry j 1.