You can transfer the immunity of someone who already has a immune defense against your illness to you. That is what a transfer factor does. Cows are exposed to various disease causing organisms and they mount a defense against them. The agent that is responsible for the defense can be extracted from the bursa of the chicken and given to a person. It is like a nation without an army hiring one when it needs it or if it is dealing with an invader, having another already trained army helping out.
Transfer factors have three functions.
First, it educates the immune system. It is like a vaccination. Secondly, it is effective at suppressing an overstimulated immune system responsible for autoimmune diseases. The immune system is modulated to work properly. Lastly, it provides memory of the disease or invader so that the person will not get it again.