Ultrastructural localization of gamma-chain and immunoglobulin G in human lymphocytes using enzyme-labeled Fab fragment.

By the use of rabbit antibodies against the heavy chain of human immunoglobulin G (IgG), the gamma-chain and IgG molecules were successfully localized at the ultrastructural level in human peripheral lymphocytes. The rabbit Fab fragment was coupled to horseradish peroxidase by means of glutaraldehyde and the resulting conjugate could penetrate the intact plasma membrane. Discernible reaction product was observed in cisternae of the nuclear envelope, rough endoplasmic reticulum and Golgi apparatus as well as on the surface of the lymphocytes. In normal human individuals under no specific antigenic stimulation, only a few peripheral lymphocytes showed a rare positive intractoplasmic reaction. Reaction product may represent either the whole IgG molecule, the half molecule consisting of one heavy and one light chain or nascent gamma-chain.