Graft Rejection: The Uninvited Guest Protocol

The ultimate biological "who are you and why are you in my house?" moment! Your immune system is basically that overprotective bouncer who doesn't care how many times you show your ID - if you're not on the list, you're not getting in. When a transplanted organ shows up, your immune cells give it that suspicious side-eye like "I don't remember inviting you to this body party." Without immunosuppressants playing referee, it's a cellular turf war where your white blood cells are ready to throw hands with any tissue that can't provide the proper biological password. It's like your body has trust issues with perfectly good organs!