Enhancement of cell-mediated immune response in chickens by combination of TIR-TLR7 with inactivated Newcastle disease vaccine

Introduction: Live and inactivated vaccines are wildly used against Newcastle disease (ND) which is a highly contagious and acute viral infection of domestic and wild birds. A higher and prolonged immune response is required to improve the control of the disease. The aim of this study was to evaluate the potential of the conserved TIR domain of an immune regulatory protein TLR7 (i.e. TIR-TLR7) as a biological adjuvant in enhancing cell-mediated immunity in vaccinated chickens against the inactivated ND virus (NDV) V4 strain antigen. Methods: NDV V4 strain was propagated in chicken embryonated SPF eggs, tittered and then inactivated by formalin. The amount of 10 μg of TIRTLR7 was mixed with the NDV antigen before intramuscular administration. Fifty SPF chickens were divided in A-E groups (n=10), consisted of negative control, TIR-TLR7, inactivated NDV antigen, TIR-TLR7/inactivated NDV antigen in prime, and the same regimen in boost platform. The blood samples were collected at week intervals up to 6 weeks post-vaccination. Humoral response was measured by detection of specific NDV antibody titer using the HI test. The cell-mediated immunity was evaluated by measuring lymphocyte proliferation in splenocytes cell culture using MTT. Results: All immunized chickens with TIR-TLR7/inactivated NDV antigen had significant (P < 0.05) cellmediated and HI responses to NDV compared to the control groups. No statistically-significant difference was observed between the prime and boost trials. Conclusion: The results indicated that the combination of TIR-TLR7 and inactivated NDV antigen gave a strong immune response at both the humoral and the cellular levels.