Mice lacking the transcription factor CIITA - a second look

We have generated a second line of mice lacking a transcription factor thou ght to be a critical regulator of MHC class II gene expression, CIITA (for class II transactivator), Our and the previously published lines differ in the deletion that was engineered and by the fact that we removed the neomyc in-resistance promoter and structural gene via the cre-IoxP recombination s ystem. Characterization of our line led to two new findings. First, a subst antial number of cells can express class II molecules in the absence of CII TA, albeit at 5-fold reduced levels, most notably dendritic cells in s.c. l ymph nodes; therefore, the CIITA gene cannot be an absolute 'master gene' c ontrolling the expression of class II molecules, as had been thought. Secon d, in contrast to recent results on human cell lines, CIITA is not critical ly involved in the IFN-gamma-induced up-regulation of MHC class I genes.