If this protein is rendered ineffective (e.g., by immuno-neutralization) by treatment of the bird with a specific antibody, then embryonic development ceases and the embryo dies.
Since it is impractical to fuse a tag to every conceivable antigen-specific antibody, most immunolabeling processes use an indirect method of detection.
To observe the rotation of single bacterial cells, the researchers attached the bacteria to a glass coverslip using a flagellar protein-specific antibody.
Humanization can be necessary when the process of developing a specific antibody involves generation in a non-human immune system (such as that in mice).