B-lymphoblastoid cell line (LCL) 721.221 lacks HLA-A, -B, and -C class I antigens and transcripts as a result of γ-ray-induced mutations. LCL 721, from which mutant .221 was derived, produces membrane and secreted forms of IgG1(κ). In contrast, IgG expression in .221 had these characteristics: (i) γ1 heavy chains were diminished by 98% but were detectable with chain-specific antibodies in cell lysates; (ii) κ light chains were present at normal levels in cell lysates and free κ chains were secreted; (iii) cell-surface-associated IgG and secreted IgG were absent. Mutants that had partially reduced amounts of class I antigens continued to secrete IgG; however, both the absolute amount of IgG secreted and the relative amount of κ vs. intact IgG secreted were abnormal in such partially class I-deficient cells. The failure to export IgG and the deficiency of HLA-A, -B, and -C were not merely coincidental in mutant .221, since production of IgG was restored by transferring a functional HLA-A, -B or -C gene into .221. Cell surface antigen expression of cloned HLA-A, -B, and -C transgenes introduced into .221 was comparable to that of the same genes in their normal chromosomal locations. These observations reveal a relation between production of HLA class I gene products and production of IgG.
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