A gene required for class II-restricted antigen presentation maps to the major histocompatibility complex.
We have previously described a set of mutants (16.23-selected mutants) of a B lymphoblastoid cell line that are defective in the presentation of intact proteins to class II-restricted T cells, but effectively present immunogenic peptides. The mutations in these mutants are recessive in somatic cell hybrids and are not in Class II structural genes. Here, we report on a unique mutant, 5.2.4, in which a similar defect in class II-restricted antigen presentation has occurred in association with a one-megabase homozygous deletion in the class II region of the major histocompatibility complex (MHC). The defects in class II presentation among three of the 16.23-selected mutants, and between these mutants and 5.2.4, are noncomplementary in somatic cell hybrids. This suggests that the class II presentation-defective phenotype in all four mutants results from lesions in a single MHC-linked gene, a conclusion strengthened by the finding that in a hybrid made with a second, unrelated MHC deletion mutant, T2, the class II presentation defect in a 16.23-selected mutant is also not complemented. Mutant 5.2.4, in addition to its class II presentation defect, is also defective in surface expression of MHC class I molecules, most likely because its deletion encompasses the peptide supply factor 1 gene, whose function is known to be required for normal abundance of cell surface class I molecules. However, the surface abundance of class I molecules is normal in the 16.23-selected mutants, suggesting that the lesions affecting class I surface abundance and class II presentation result from mutations in different genes.
Mellins
E
E
Department of Pediatrics, University of Washington 98105.
Kempin
S
S
Smith
L
L
Monji
T
T
Pious
D
D
D000938:Antigen-Presenting Cells / Q000502:physiology*; D000954:Antigens, Surface / Q000032:analysis; D002872:Chromosome Deletion; D002874:Chromosome Mapping; D005802:Genes, MHC Class II; D015395:Histocompatibility Antigens Class I / Q000032:analysis; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D006720:Homozygote; D009154:Mutation; D010641:Phenotype
D000954:Antigens, Surface; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II