The protective effect of γ-aminobutyric acid on the development of immune function in chickens under heat stress

This study aimed to investigate the protective effect of γ-aminobutyric acid (GABA) on the development of immune function in chicks under heat stress (HS). One-day-old male Wenchang chicks were randomly divided into control (CK), HS and GABA+HS groups. The GABA+HS group was fed with 0.2 ml GABA solution (50 mg/kg) daily by oral gavage. The HS and GABA+HS groups were placed in 40 ± 0.5 °C environment for 2 h heat treatment from 13:00 each day. Blood samples were routinely taken at 14, 21, 28, 35 and 42 days respectively, and the contents of T and B lymphocyte subsets in the blood and tissue were analysed by flow cytometry after FITC/PE double staining; the plasma levels of interleukin (IL)-2, immunoglobulin (Ig)A, IgG and IgM were determined using ELISA. The thymus and the bursa of fabricius were also collected to analyse for organ index and observe for the changes in tissue microstructure. In addition, the chicks received primary and secondary immunizations with attenuated Newcastle disease (ND) vaccine (LaSota strain) at 7 and 28 days respectively; conventional hemagglutination inhibition (HI) assay was performed to monitor the titre changes in plasma antibody against ND virus in the birds. Our results indicated that the indices of both thymus and bursa of fabricius, the intactness of tissue structure and development, the plasma levels of IL-2, IgA, IgG and IgM, the titres of ND antibody, and the levels of B and T lymphocyte subsets in HS group were all significantly lower than those in CK group (p < 0.05). However, all above indices were significantly improved in GABA+HS group compared with those in HS group (p < 0.05). These results demonstrated that while HS seriously affected the development of immune function in Wenchang chicks, GABA effectively alleviated the damages of HS to the development of immune function in chicks.