This document discusses immunofluorescence, a technique used to detect antibodies in serum or body fluids. It involves using a primary antibody that binds to the target antigen, then a fluorescent secondary antibody that binds to the primary. This allows visualization under a microscope. Two types are described: direct uses a fluorescent primary antibody, indirect uses a non-fluorescent primary and fluorescent secondary for signal amplification. Applications include detecting autoantibodies associated with various diseases by looking for fluorescence patterns on tissue sections like Hep-2 cells or mouse organs. Indirect immunofluorescence is considered the standard technique as it has high sensitivity and specificity.