English: This figure demonstrates the basic mechanism of immunofluorescence. Primary immunofluorescence is depicted to the left, which shows an antibody with a fluorophore group bound to it directly binding to the epitope of the antigen it’s specific for. Once the antibody binds to the epitope, the sample can be viewed under fluorescent microscope to confirm the presence of the antigen in the sample. Conversely, secondary immunofluorescence is depicted to the right, which shows that first an untagged primary antibody binds to the epitope of the antigen in a mechanism similar to the one described above. However, after the primary antibodies have bound to their target, a secondary antibody (tagged with a fluorophore) comes along. This secondary antibody’s binding sites are specific for the primary antibody that’s already bound to the antigen, and therefore the secondary antibody binds to the primary antibody. This method allows for more fluorophore-tagged antibodies to attach to their target, thus increasing the fluorescent signal during microscopy.