Infectious bronchitis (IB) is a notable disease of poultry flocks that results in economic loss. As a consequence of the presence of various IB virus (IBV) serotypes, control strategies, such as vaccination, should be replaced by provide broad protective immunity against the disease to date. Gram-positive enhancer matrix particles, or so-called bacterium like particles (BLPs), obtained from the bacterium Lactococcus lactis (L. lactis), have demonstrated an adjuvancy effect by providing demanding mucosal and humoral immune responses, as well as a protective cellular immunity whenever delivered admixed with a vaccine via intranasal or intraocular administration. In this study, for the first time, attempts were made to investigate the impact of an IBV vaccine supplemented by various doses of BLPs on induced levels of humoral immunity against IB. For this purpose, increasing doses of derived BLPs (0, 0.15, 0.3, and 0.6 mg dry weight per bird) were admixed with IBV live attenuated H120 serotype vaccine, and were delivered via ocular administration to 4 equal groups of 10 specific pathogen-free (SPF) chickens in 4 groups: control, BLP1, BLP2, and BLP3, respectively. In addition, 10 SPF chickens that were not immunized comprised the Unvaccinated group. Blood was collected from 5 members of each group weekly for 35 days. Levels of IgG antibodies in the sera were then assayed using ELISA. Weight gain and the feed conversion ratio of each group were also recorded weekly. Finally, 3 birds from each group were necropsied to evaluate probable lesions. The best results were obtained in the BLP1 group, with IBV vaccination at a low dose of admixed BLPs boosted immediate anti-IBV humoral responses; however, the results were not significantly different from those of the Control group, but were still feasible enough for application in the field. In conclusion, BLPs could be a desirable adjuvant for IBV vaccines to increase immunity in chickens.

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