Trained immunity against diseases in domestic animals

Trained immunity is a biological concept that has been demonstrated in different animal species, including human beings. Evidences indicate that innate immune cells can be trained and have a "memory". Under this concept, studies have shown that a first stimulus can potentiate immune responses upon a second one or protect upon homologous or heterologous pathogenic challenges. Research progress on trained innate immunity in mouse models and human beings has provided key information of this phenomenon. In domestic animals, this concept offers a heterologous protection against diseases. Recent studies in domestic animals have demonstrated that trained immunity is induced even by mucosal routes rather than only parenteral routes, as previously evidenced in mice and humans. This situation has led to a major breakthrough in the biotechnology field. Remarkably, the recent first proof-of-concept in calves and goats provides a reality beyond trained immunity as an affordable immunobiotechnological approach to control diseases. Currently, several responses to questions that have been deciphered in mouse and humans seem different in domestic animals; even these differences have been observed among animal species and breeds, which open new questions and challenges. The information of mechanistic studies in domestic animals based on the trained immunity paradigm has not been integrated before; therefore, it needs to be discussed and accurately presented. Moreover, prospects should be defined and biotechnological perspectives provided to promote research and development (R&D) to become a near reality in domestic animal, so this is the main objective of the review.