RESUMEN
The effect of tilmicosin, florfenicol, or enrofloxacin on humoral and cell-mediated immune response induced by Newcastle disease (ND) vaccination was evaluated in 20-wk-old specific-pathogen-free layer chickens. Humoral immunity was measured by detection of ND virus (NDV) antibody titer and anti-NDV IgG response using the hemagglutination inhibition (HI) test and ELISA, respectively, whereas cell-mediated immunity was evaluated by measurement of chicken interferon gamma (ChIFN-gamma) produced in splenocytes cell culture stimulated with concanavalin A, inactivated NDV antigen, or live attenuated La Sota strain using ELISA. Florfenicol hampered the ND antibody production measured by both HI and ELISA. Tilmicosin and enrofloxacin reduced the production of ND antibody in the first 3 wk after the last ND vaccination measured by HI test, which suggests that these antibiotics exert their effect mainly on the IgM isotype. The ND-vaccinated, but not treated group, showed an increase in ChIFN-gamma production after NDV antigen-specific stimulation above the nonstimulated cell culture, whereas this effect was masked in all the antibiotic-treated groups due to the stronger ChIFN-gamma production background value reported in the nonstimulated cell culture. In conclusion, our results showed, for the first time, that tilmicosin, florfenicol, or enrofloxacin reduced the humoral immune response and had beneficial effects on the cell-mediated immune response. In addition, we demonstrated that the combination of both inactivated and attenuated ND vaccine gave a strong immune response at both the humoral and cellular level.