Complex regulation of class II gene expression: analysis with class II mutant cell lines
Glimcher, L.H.; McKean, D.J.; Choi, E.; Seidman, J.G.
Journal of Immunology 135(5): 3542-3550
1985
ISSN/ISBN: 0022-1767 PMID: 2995495 Document Number: 257266
Several Ia-negative variants of a homozygous Iad-expressing antigen-presenting B lymphoma cell line, M12, have been obtained by repeated cycles of negative immunoselection after mutagenesis with ethylmethane sulfonate or .gamma.-irradiation. Two such Iad-negative cell lines, selected with a mixture of .alpha.I-Ad and .alpha.I-Ed monoclonal antibodies, failed to present antigen to all cloned Iad-restricted T cells tested, whereas the third cell line, selected with .alpha.I-Ad reagents only, stimulated I-Ed but not I-Ad-restricted T cells. The mutations in all three cell lines resulted in the absence of RNA specific for the A.beta.d gene. In addition, two-dimensional gel electrophoresis of immunoprecipitates from one of the I-Ed-negative cell lines demonstrated the presence of intracytoplasmic Ed plypeptides that exhibited significantly decreased amounts of oligosaccharide-induced heterogeneity. The introduction of class II A.beta.b and A.alpha.b genes by DNA-mediated transfection resulted in the serologic and functional expression of a class II I-Ab molecule but not the reexpression of the endogenous class II molecules; thus a transacting regulatory element is unlikely to be the target of the mutagenic event. The analysis of these and other Ia variant cell lines may prove useful in understanding the molecular mechanisms that control the expression of class II molecules in B cells.