Same scenario as previous question: A tumor biopsy is proces…

Same scenario as previous question: A tumor biopsy is processed for immunohistochemistry (IHC) to detect Ki-67, a nuclear marker of cell proliferation. The sample is incubated first with a rabbit anti–Ki-67 antibody, then with a goat anti-rabbit IgG antibody conjugated to alkaline phosphatase (AP). After adding the Fast Red substrate, red staining appears specifically in the nuclei of dividing cells. What are the roles of the primary and secondary antibodies?