In immunofluorescence microscopy, fluorophore labeled antibodies emit fluorescence upon binding a specific target or an antigen. Immunofluorescence microscopy uses light to excite electrons of the fluorophore to a higher energy state. As they return to the ground state, the electrons release a longer wavelength of light. This emission or fluorescence allows visualization of specific cells within tissues or particular proteins within cells. Immunofluorescence can be direct when the primary fluorophore-tagged antibody binds to the target protein. Or, it can be indirect, where secondary antibodies tagged with fluorophores bind a specific primary antibody attached to the protein of interest. The resulting fluorescence is stronger than that emitted by direct immunofluorescence. Direct immunofluorescence is used to detect abnormal protein aggregation in tissues, while indirect immunofluorescence can detect the circulating antibodies in the serum during autoimmune disease diagnosis.