Isolation and characterization of a new murine MHC class II transcription mutant cell line

We have isolated and characterized a new MHC class II transcription mutant cell line, called UV. This cell line was derived from the mouse B lymphoma A20 by UV light-induced mutagenesis and immunoselection for the loss of surface MHC class II molecules. It expresses only 5% of the level of MHC class II molecules on A20 and this is associated with a similar reduction of class II specific mRNA. This defect cannot be restored by the MHC class II transcription inducers, IL-4 and IFN gamma, confirming that the mutation acts at the transcription level. The mutation also affects MHC class I expression, but the transcription of class I molecules is not affected. In contrast, the expression of other markers, such as the invariant chain and the surface immunoglobulins G and M, is not modified. Such a variant should prove useful for the study of the transcription factors involved in the regulation of MHC class II expression.