Serum IgG response in calves to the putative pneumonic virulence factor Gs60 of Mannheimia haemolytica A1

Bovine pneumonic pasteurellosis vaccines incorporate various antigens of Mannheimia haemolytica, including the acknowledged virulence factor leukotoxin (Lkt), and Gs60, a surface lipoprotein. To examine the role of antibodies to Gs60 in protection, an enzyme-linked immunosorbent assay (ELISA) was developed for retrospective analysis of serum samples from previous trials in which vaccines containing native or recombinant Gs60 were administered parenterally. The analysis revealed a positive correlation between the titer of antibodies to Gs60 and protection against experimental challenge in both vaccinates and naturally exposed controls. There was a strong correlation between production of IgG antibodies to Gs60 and Lkt neutralizing antibodies. Analysis of the relationship between the serum antibody titers and resistance to experimental challenge using linear statistical models revealed a significant association between prechallenge titers of serum antibodies to Lkt and protection. Further analysis suggested that antibodies against Gs60 were beneficial when Lkt neutralizing antibody titers were low.

A toll-like receptor 3 ligand enhances protective effects of vaccination against Marek's disease virus and hinders tumor development in chickens

Marek's disease (MD) is caused by Marek's disease virus (MDV). Various vaccines including herpesvirus of turkeys (HVT) have been used to control this disease. However, HVT is not able to completely protect against very virulent strains of MDV. The objective of this study was to determine whether a vaccination protocol consisting of HVT and a Toll-like receptor (TLR) ligand could enhance protective efficacy of vaccination against MD. Hence, chickens were immunized with HVT and subsequently treated with synthetic double-stranded RNA polyriboinosinic polyribocytidylic [poly(I:C)], a TLR3 ligand, before or after being infected with a very virulent strain of MDV. Among the groups that were HVT-vaccinated and challenged with MDV, the lowest incidence of tumors was observed in the group that received poly(I:C) before and after MDV infection. Moreover, the groups that received a single poly(I:C) treatment either before or after MDV infection were better protected against MD tumors compared to the group that only received HVT. No association was observed between viral load, as determined by MDV genome copy number, and the reduction in tumor formation. Overall, the results presented here indicate that poly(I:C) treatment, especially when it is administered prior to and after HVT vaccination, enhances the efficacy of HVT vaccine and improves protection against MDV.

In vivo administration of ligands for chicken toll-like receptors 4 and 21 induces the expression of immune system genes in the spleen

Toll-like receptors (TLRs) are a group of conserved proteins that play an important role in pathogen recognition in addition to the initiation and regulation of innate and adaptive immune responses. To date, several TLRs have been identified in chickens, each recognizing different ligands. TLR stimulation in chickens has been shown to play a role in host-responses to pathogens. However, the mechanisms through which TLRs modulate the chicken immune system have not been well examined. The present study was conducted to characterize the kinetics of responses to TLR4 and TLR21 stimulation in chickens following intramuscular injections of their corresponding ligands, lipopolysaccharide (LPS) and CpG oligodeoxynucleotides (ODNs), respectively. To this end, relative expression of cytokine genes in the spleen was determined at 2, 6, 12 and 24 h after injection of TLR ligands. The results indicated that LPS strongly induced the up-regulation of some immune system genes early on in the response to treatment, including interferon (IFN)-γ, interleukin (IL)-10, and IL-1β. Furthermore, treatment with CpG ODN promoted the up-regulation of major histocompatibility complex (MHC)-II, IFN-γ and IL-10. The response to CpG ODN appeared to be somewhat delayed compared to the response to LPS. Moreover, we found a significant increase in IFN-α gene expression in response to LPS but not CpG ODNs. Future studies may be aimed to further characterize the molecular mechanisms of TLR activation in chickens or to exploit TLR agonists as vaccine adjuvants.