Mutant human cells defective in induction of major histocompatibility complex class II genes by interferon gamma.

Using immunoselection, we have isolated 11 independent mutant HT1080 fibrosarcoma cell lines defective in the induction by interferon gamma (IFN-gamma) of the expression of the human leukocyte antigen HLA-DRA. The mutations are recessive and fall into five complementation groups. All the mutants are affected mainly in the expression of major histocompatibility complex class II and invariant-chain genes. Type I mutants (three complementation groups) are completely defective in induction of the invariant-chain and class II HLA-DP, -DQ, -DR, and -DM genes, whereas type II mutants (two complementation groups) induce these genes weakly in response to IFN-gamma, in the order DPB > DRA > invariant chain. The induction by IFN-gamma of the mRNAs for class I, TAP1, LMP7, and 9-27 is partially defective and the induction of the proteins IRF-1 and ICAM-1 is normal in both types of mutants. All the mutants respond normally to IFN-alpha. The mutants are stable and thus can be used to clone the affected genes by reversion.