Evaluation of Immunomodulatory Role of Bacterial LPS During Embryonic Development in Chicken

Toll like receptor (TLR) agonists are largely viewed as potential vaccine adjuvants to modulate both innate as well as adaptive immune response. The present study was undertaken to explore at what extent the chicken immune system at embryonic stages can respond towards the antigen in association with Lipopolysaccharide (LPS) and its outcome on humoral and cellular immune response. LPS was extracted from Salmonella Gallinarum, purified, characterized and confirmed by standard procedures. The LPS was used for in vitro and in vivo studies. It was found that LPS was lethal to mice and 10 days old embryonated chicken eggs but not for chicken at post-hatch period. In vivo effect of LPS was studied as an adjuvant with a model antigen Bovine serum albumin (BSA). The groups received LPS prior to BSA elicited higher immune response directed against BSA as compared to groups received BSA alone. Antibody directed against BSA was detectable in those chicks which were exposed only once during embryonic life (18th day) and LPS in association with BSA (although not chemically conjugated) was superior to BSA alone which signifies the modulatory role played by LPS. In vitro nitric oxide production varied and it was found to be increased in a time dependent manner. The LPS pre-sensitization enhanced immune response to New castle disease vaccine and protected birds against challenge. Taken together these results showed that LPS can be used as an adjuvant in chicken without any modification to modulate the immune system.