Characterization of innate responses induced by in ovo administration of encapsulated and free forms of ligands of Toll-like receptor 4 and 21 in chicken embryos.

Toll-like receptors (TLRs) are a family of innate receptors that recognize pathogen-associated molecular patterns, including double-stranded RNA, CpG DNA and lipopolysaccharide (LPS). After interaction with their ligands, TLRs initiate innate responses that are manifested by activating cells and inducing expression of cytokines that help mediate adaptive immune responses. TLR ligands (TLR-Ls) have the potential to be used prophylactically (alone) or as vaccine adjuvants to promote host immunity. Encapsulating TLR-Ls in nanoparticles, such as Poly (d,l-lactic-co-glycolic acid), may prolong responses through sustained release of the ligands. PLGA nanoparticles protect encapsulated TLR-Ls from degradation and extend the half-life of these ligands by reducing their rapid removal from the body. In this study, encapsulated and free forms of LPS and CpG ODN were administered to embryonation day 18 (ED18) chicken embryos. Spleen, lungs and bursa of Fabricius were collected at 6, 18 and 48hour post-stimulation (hps) and cytokine gene expressions were evaluated using quantitative real-time PCR. Results indicate that both the free and encapsulated forms of LPS and CpG ODN induced innate immune responses in ED18 chicken embryos. Innate responses induced in embryos seem similar to those reported in mature chickens. Significant upregulation of cytokine genes generally occurred by 48hps. Further studies are needed to evaluate long term immunomodulatory effects of encapsulated TLR-Ls and their ability to mediate protection against pathogens of young chicks.