Mycobacterial infection is a major problem in both human and animal health. Mycobacterium avium is of considerable importance to the poultry industry in many countries. This study was designed to compare the immunological interactions of different strains of M. avium subspecies avium from human and animal sources with avian in vitro and in vivo infection models.

Avian macrophage-like HD11 cells were infected with eight clinical isolates of M. avium and forty eight chickens were infected with three of these isolates. Invasiveness was measured by bacterial recovery from HD11 cells and from blood, liver and spleen of the chickens. The levels of cytokine and chemokine production were quantified using RT-qPCR at different time point post-infection both in vitro and in vivo. Histopathological examinations have performed on livers and spleens of the infected chickens.

In HD11 cells, up-regulation of iNOS, IL-1β, IL-6, CXCLi1 and CXCLi2 for all eight isolates were observed, although there were some differences between the isolates. The number of M. avium colonies in spleen and liver of all infected chickens declined during the course of the experiment suggesting that the birds were resistant to infection. Up-regulation of iNOS, IL-1β, IL-6, CXCLi2 and IFN-γ in infected chickens occurred at 21 days post-infection. No significant differences were observed between the groups infected with the different M. avium isolates. Histopathological examination revealed formation of granulomata in M. avium infected chickens livers at 21 days post-infection.

In chickens, the up-regulation of cytokines and chemokines and histopathological changes observed at 21 days post-infection confirm the chronic nature of the infection. Our data support the concept of a general similarity between the immune response to mycobacterial infection in avian species, humans and mice.