A gene required for class II-restricted antigen presentation maps to the major histocompatibility complex

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• B lymphoblastoid cell lines can be engineered to study antigen presentation.
• Defects in antigen presentation impact T cell responses.
• Major histocompatibility complex (MHC) genes are crucial for antigen presentation.

Purpose of the Study:

• To investigate the genetic basis of defects in antigen presentation.
• To characterize a unique mutant (5.2.4) with a deletion in the MHC class II region.
• To determine if defects in antigen presentation in different mutants map to the same gene.

Main Methods:

• Somatic cell hybridization to assess complementation of antigen presentation defects.
• Analysis of B lymphoblastoid cell line mutants (16.23-selected and 5.2.4).
• Characterization of major histocompatibility complex (MHC) class I and class II presentation.

Main Results:

• Three 16.23-selected mutants and the 5.2.4 mutant exhibit non-complementing defects in MHC class II antigen presentation.
• The unique mutant 5.2.4 has a homozygous deletion in the MHC class II region and is also defective in MHC class I surface expression.
• 16.23-selected mutants show normal MHC class I surface expression, indicating separate genetic lesions for class I and class II defects.

Conclusions:

• The antigen presentation defect in the studied mutants likely results from lesions in a single MHC-linked gene.
• Mutant 5.2.4's deletion likely encompasses the peptide supply factor 1 gene, affecting MHC class I expression.
• Distinct genes control MHC class I surface abundance and MHC class II antigen presentation.