Viruses of all subtypes may be introduced into domestic poultry, but only H5 and H7 low pathogenicity avian influenza viruses can mutate during circulation in poultry and emerge as high pathogenicity avian influenza variants. It is therefore essential to monitor the field situation continuously to detect low pathogenicity notifiable avian influenza (LPNAI) as soon as possible. With the emergence of the highly pathogenic H5N1, markers of infection of avian influenza are becoming more and more significant. They are important as early warning systems, and they can also be valuable tools as companion tests of vaccines (differentiating infected from vaccinated animals), but they might also be informative about the evaluation of the degree of adaptation and the timing of infection. Therefore, several experimental infections of specific-pathogen-free chickens were conducted to follow the kinetics of antibody responses against the hemagglutinin, the neuraminidase, the nucleoprotein, and the M2e after infections with LPNAI viruses isolated from waterfowl or already adapted to chicken. Overall, the immune responses against the different antigens showed similar kinetics in the different infected animals, but they were lower when the animals were infected with AI viruses originating from waterfowl, and the kinetics of the M2e antibodies was quite different. Indeed, it was rather shorter and disappeared more rapidly (approximately 35 days postinfection) compared to the kinetics of the other antibodies. Therefore, the detection of the antibodies against M2e peptide could be an interesting tool to detect recent infection, and these preliminary results indicated that the production of M2e antibodies might be correlated with the degree of adaptation of LPNAIs.
