S. Ceman et al., GENE REQUIRED FOR NORMAL MHC CLASS-II EXPRESSION AND FUNCTION IS LOCALIZED TO APPROXIMATELY 45 KB OF DNA IN THE CLASS-II REGION OF THE MHC, The Journal of immunology, 152(6), 1994, pp. 2865-2873
In certain mutant human B cell lines, MHC-encoded class II molecules d
isplayed at the cell surface have an abnormal conformation and are uns
table in the presence of SDS. The mutants cannot present exogenous pro
tein Ags to T cells but elicit responses with exogenous antigenic pept
ides; thus, formation of intracellular complexes between antigenic pep
tides and class II molecules is impaired. Previous analysis of LCL del
etion mutants, .82, .174, and 5.2.4, showed that genes needed for this
function must be present in approximate to 230 kb of DNA in the class
II region of the MHC. We now describe a new deletion mutant, .61, whi
ch has normal class II-mediated Ag processing/presentation. The TAP1,
TAP2, LMP2, and LMP7 genes are deleted from .61, demonstrating that th
ose genes are not needed for normal formation of intracellular class I
I/peptide complexes. The genes in question must be located in DNA that
is present in .61 and .82 (both normal) and absent from .174 and 5.2.
4. (both defective). Mapping of the deletion breakpoints indicates tha
t genes needed for normal class II-associated Ag processing/presentati
on are either: 1) in an approximate to 40 kb L DNA segment located bet
ween the DMB and LMP2 loci or 2) in an R region between the DQA2 and D
QB1 loci and are completely included on a 5.1-kb fragment formed by jo
ining of DNA that flanks the deletion in .61. The evidence favors loca
tion of the genes in the L DNA segment.