Immunogenic and protective efficacy of recombinant protein GtxA-N against Gallibacterium anatis challenge in chickens

Gallibacterium anatis is a major cause of reproductive tract infections in chickens. Here, we aimed to evaluate the efficacy of the recombinant protein GtxA-N at protecting hens, by addressing three objectives; (i) evaluating the antibody response following immunization (ii) scoring and comparing lesions, following challenge with G. anatis, in immunized and non-immunized hens and (iii) investigating if the anti-GtxA-N antibody titre in individual hens correlated with the observed lesions. Two consecutive experiments were performed in hens. In the first experiment hens were immunized with GtxA-N on day 0 and day 14, infected with G. anatis on day 28 and euthanized on day 56. The GtxA-N antibody response was assessed in pooled serum samples throughout the experiment, using an indirect enzyme-linked immunosorbent assay (ELISA). In the second experiment the GtxA-N antibody titres were assessed in individual hens before and after immunization. Subsequently, the hens were inoculated with G. anatis and finally all hens where euthanized and submitted for post mortem examination 48 h after inoculation. Immunization elicited strong antibody responses that lasted at least 8 weeks (P < .0001). The individual antibody titres observed in response to immunization varied considerably among hens (range: 174,100-281,500). Lesion scores following G. anatis infection were significantly lower in immunized hens compared to non-immunized hens (P = .004). Within the immunized group, no correlation was found between the individual antibody titres and the lesion scores. This study clearly demonstrated GtxA-N as a vaccine antigen able of inducing protective immunity against G. anatis.