Macrophages , heterophils and thrombocytes are the main cells associated with the nonspecific immune system. Once the antigen is presented and in turn processed by the B and T cells, the antibody is produced that will mark it and bind it to be culled from the body by the spleen and liver. This encounter is also filed away in memory cells so response will be faster should this same antigen be confronted again. Birds differ from mammals in the way their immune system develops and becomes diverse enough to meet lifelong challenges, with a unique organ called the bursa and a process called gene conversion. Baby birds are born with an incomplete immune system.
Maternal immunity is passed on in the amniotic fluid and yolk of the egg.
The bird's immune system begins developing before hatch and is complete by sexual maturity. One of the most important stages of this development happens in the first six weeks of the chick's life, when gene conversion is taking place in the bursa. If left this way, the B lymphocytes will not be able to produce the different antibodies needed to resist specific diseases. So for the first six weeks of the bird's life, these B cells go to school in the bursa, where they are rearranged in order to provide the diversity needed to protect against the great variety of potential pathogens. The bursa continues to produce B cells until it involutes at sexual maturity and then the blood marrow takes over the task of producing the B cells.