Immunostaining is a lab technique used to detect specific proteins or antigens in cells or tissues, commonly through immunohistochemistry (ihc) or immunofluorescence (if). A primary antibody binds to the target protein, and a secondary antibody with a visible marker, such as a fluorescent dye (for if) or enzyme (for ihc), attaches to the primary antibody, highlighting the protein's location. This technique is essential for research in pathology, cancer diagnostics, and cell biology.