PROS1 and Newcastle disease: In this study, Fecto and the IBV S1 protein were fused to the TM and CT domain of the IBV S protein (STMCT), forming the recombinant F (rF) and recombinant S (rS) protein, respectively, and chimeric infectious bronchitis-Newcastle disease (IB-ND) VLPs were constructed with these two recombinant proteins and IBV M proteins through the baculovirus system.