THRESHOLD DETECTION OF SELF-ANTIGEN MHC CLASS-II COMPLEXES FORMED IN-VIVO - CONSTITUTIVE PRESENTATION OF AN IMMUNODOMINANT EPITOPE OF HEN EGG LYSOZYME (HEL) IN HEL-TRANSGENIC MICE

Hen egg lysozyme (HEL)-specific T hybridomas were used to study the pr esentation of HEL as a self component in tolerant, HEL-transgenic mice expressing different serum levels of HEL (AL3, 3-7 nM: ML5, 1-3 nM). Constitutive presentation of the HEL46-61 determinant was detectable i n antigen presenting cell (APC)-enriched preparations of spleen, thymu s, and lymph node from AL3 transgenic mice. The most likely cell respo nsible for constitutive presentation of HEL antigen was a non-B cell. In addition, constitutive presentation of HEL46-61 Was clearly evident in thymic rosettes (complexes of macrophages or dendritic cells and l ymphoid cells) derived from AL3 HEL-transgenic mice, but not from ML5 HEL-transgenic mice. In contrast to the HEL46-61 determinant, constitu tive presentation of the HEL25-43 and HEL112-129 determinants was not detectable on APC-enriched preparations from either of the HEL-transge nic lines tested. Thus, although T cell tolerance was evident in trans genic mice expressing a range of serum HEL concentrations, constitutiv e presentation of processed HEL antigen was not detectable on APCs fro m mice expressing less than 3-7 nM. This threshold of detectable antig en presentation is consistent with the notion that the concentration o f nominal antigen needed for tolerizing T cells is less than that requ ired for activation of mature T cells.