Presentation of endogenous immunoglobulin determinant to immunoglobulin‐recognizing T cell clones by the thymic cells

Using immunoglobulin (Ig)‐recognizing T helper clones the expression of Ig peptide/major histocompatibility complex class II complexes derived by the processing of endogeneous Ig molecules in the thymus was demonstrated. It was found that thymic B cells but not “classic” thymic antigen‐presenting cells and macrophages represent the major antigen‐presenting cell type of determinants of endogenously synthesized surface Ig (Igx‐1b) and anti‐surface Ig antibodies (IdC3B9). The Igx‐1b‐presenting activity in the thymus appears relatively late, only after 3 weeks of postnatal life, while in the spleen an efficient presentation of endogenous Igx‐1b epitope is observed very early after birth. This difference between thymic and peripheral presentation of endogeneous Ig determinant could be important for understanding the mechanisms of T cell tolerance to self Ig and the role of self Ig in negative and positive selection of T cell repertoire.