Abstract Under the dual pressure of emerging zoonoses and the difficulty in eliminating conventional zoonoses, the strategic management of bird diseases through vaccination represents a highly efficacious approach to disrupting the transmission of zoonotic pathogens to humans. Immunization with a DNA vaccine yielded limited protection against avian pathogen infection. To improve its immunogenicity, the extracellular domain of duck-derived CD40L (designated as dusCD40L) was employed as a bio-adjuvant. Our findings unequivocally established the evolutionary conservation of dusCD40L across avian species. Notably, dusCD40L exhibited a compelling capacity to elicit robust immune responses from both B and T lymphocytes. Furthermore, when employed as an adjuvant, dusCD40L demonstrated a remarkable capacity to significantly augment the titers of neutralizing antibodies and the production of IFNγ elicited by a DNA vaccine encoding the prM-E region of an avian flavivirus, namely, the Tembusu virus (TMUV). Moreover, dusCD40L could strengthen virus clearance of the prM-E DNA vaccine in ducks post-TMUV challenge. This research study presents a highly effective adjuvant for advancing the development of DNA vaccines targeting TMUV in avian hosts. Additionally, it underscores the pivotal role of duCD40L as a potent adjuvant in the context of vaccines designed to combat zoonotic infections in avian species.
