Thymus Localization of Monoclonal Antibodies Circumventing the Blood‐Thymus Barrier

The binding in the rat thymus of mouse monoclonal antibodies which recognize determinants present on class II major histocompatibility complex antigens (HIS 19) and all T cells (HIS 17) was studied at several intervals after in vivo injection of a single dose (8 mg)of the monoclonal antibodies (MoAb). The MoAb, injected either intravenously or intraperitoneally. penetrated the thymus initially across the thymic capsule from the extravascular space. The extent to which the MoAb penetrated both cortex and medulla correlated with serum presence of the monoclonal antibody. These results suggest that the thymus cortex and medulla are permeable to MoAb present in the extravascular compartment. if this situation is a general phenomenon, which applies to circulating self non‐major histocompatibility complex antigens under physiological conditions, the current dogma relating to self‐tolerance needs to be reviewed.