CLONAL DELETION OF SPECIFIC THYMOCYTES BY AN IMMUNOGLOBULIN IDIOTYPE

We have investigated whether immunoglobulin can induce clonal deletion of thymocytes by employing two strains of transgenic mice. One strain is transgenic for an alpha/beta T cell receptor (TCR) which recognizes a processed idiotypic peptide of the lambda2(315) light chain variable region, bound to the I-E(d) class II major histocompatibility complex molecule. The other mouse strain is transgenic for the lambda2(315) gene. Double transgenic offspring from a TCR-transgenic female mated with a lambda2(315) transgenic male exhibit a pronounced clonal deletion of CD4+CD8+ thymocytes. Analysis of neonates from the reciprocal (lambda2(315)-transgenic female X TCR-transgenic male) cross suggests that the deletion in double transgenic offspring most likely is caused by lambda2(315) produced within the thymus rather than by maternally derived IgG, lambda2(315). Nevertheless, IgG, lambda2(315) can cause deletion of CD4+CD8+ thymocytes when injected in large amounts intraperitoneally into either adult or neonatal TCR-transgenic mice. Deletion is evident 48 and 72 h after injection, but by day 7 the thymus has already regained its normal appearance. A serum concentration of several hundred Ag/ml is required for deletion to be observed. Therefore, the heterogeneous idiotypes of serum Ig are probably each of too low concentration to cause thymocyte deletion in normal animals.