Final answer:
The correct term for the technique where antibodies are tagged with a fluorophore to locate a protein within a cell is immunofluorescence, which can be applied directly to target pathogens or indirectly to detect specific antibodies.
Step-by-step explanation:
The technique where antibodies are conjugated to a fluorophore to detect the location of a specific protein within a cell is known as immunofluorescence. This method utilizes fluorochrome-labeled antibodies, which, when bound to their specific antigen, can be visualized under a fluorescence microscope due to their ability to emit light upon excitation. Direct immunofluorescence involves labeling the antibodies that directly target the antigen of interest, while indirect immunofluorescence uses a secondary antibody that recognizes the primary antibody bound to the antigen.
In the context of clinical samples, such as searching for bacteria in sputum, direct immunofluorescence can rapidly detect the presence of the pathogen. Similarly, in the context of an immune response, indirect immunofluorescence can identify antigen-specific antibodies in patient sera. Various types of cells can be quantified using these methods, for example, measuring the level of CD4 T cells in HIV patients using flow cytometry with fluorescently labeled antibodies.