isotypespecific

Isotype-specific (also written isotypespecific) describes reagents, assays, or observations that discriminate among immunoglobulin isotypes or subclasses (for example IgG, IgA, IgM, IgD, IgE, and IgG subclasses IgG1–IgG4). An isotype-specific antibody binds to the constant region of a particular heavy chain, allowing selective detection, purification, or modulation of antibodies of that isotype.

In laboratory practice, isotype-specific reagents are used in ELISA and Western blot to detect antibodies of a given isotype, in flow cytometry to phenotype B cells or plasma cells, and in immunohistochemistry to localize isotype-expressing cells in tissues. They are also used in subclass profiling to characterize immune responses, for example measuring IgG subclass distribution in infections or immunodeficiencies.

Isotype controls are related but distinct: they are antibodies of the same isotype as the primary antibody but lacking specificity for the target antigen, used to assess non-specific binding.

Important limitations include potential cross-reactivity between similar constant regions, species reactivity, and batch-to-batch variation; proper validation and controls are essential.

See also immunoglobulin isotypes; heavy chain constant region; monoclonal antibody; isotype control.