In the indirect immunofluorescence method, what is the labeled antibody used to detect antibodies in a patient's serum?

In the indirect immunofluorescence method, the labeled antibody used to detect antibodies in a patient's serum is typically a goat anti-human immunoglobulin. This method relies on the use of a secondary antibody that is specific to the human immunoglobulin, thus allowing for the visualization of the binding between the patient’s serum antibodies and the antigen on the slide.

Goat anti-human immunoglobulin is particularly favored for several reasons. Goats can produce a high yield of antibodies, and the antibodies generated against human immunoglobulin have a broad reactivity to different classes and subclasses of human antibodies. The use of goat as a source also minimizes cross-reactivity with other species' antibodies, making it a reliable choice for detecting human antibodies in various clinical specimens.

The labeling of the goat antibody with a fluorescent dye allows for easy visualization under a fluorescence microscope, where the specific binding can be detected, highlighting the presence of antibodies in the patient's serum. This technique is widely used in clinical immunology for diagnosing autoimmune diseases and state of immune responses.