γ-Aninobutyric acid (GABA) suppresses antigen-specific immune responses in ovalbumin γ(OVA)-immunized BALB/c mice

γ-Aminobutruic acid (GABA) is known to be a ubiquitous inhibitory neurotransmitter in the central nervous system. Furthermore, recent studies have shown that GABA modulates cardiovascular and respiratory functions. In this study, we examined the effect of GABA on antigen (Ag)-specific immune responses and elucidated the mechanisms underlying those effects in ovalbumin (OVA)-immunized BALB/c mice. OVA-specific proliferative responses were decreased in mice that had been administered 20 mg/kg GABA compared to those in control mice without reduction in responses to anti-CD3 monoclonal (m)Ab. The levels of OVA-specific IgG, IgG1 and IgG2a were also decreased in mice that had been administered GABA. However, GABA administration did not influence the TNP-specific IgM and IgG levels. Ag-presenting activity of CD11c⁺ dendritic cells from GABA-treated mice was less than that of cells from control mice. These results suggest that the suppressive effect of GABA on Ag-specific immune responses contributes to the reduction of antigen-presenting function on CD11c⁺ dendritic cells.