Zemmour J, Little A M, Schendel D J, Parham P
Department of Cell Biology, Stanford University, CA 94305-5400.
J Immunol. 1992 Mar 15;148(6):1941-8.
The HLA-A,B negative mutant cell line C1R is widely used as a transfection recipient in functional studies of class I MHC genes. It was derived from a normal B cell line, Hmy2, by three rounds of mutagenesis and immunoselection with anti-HLA mAb. Serology characterizes C1R to be negative for the HLA-A2, A3, B35, Bw62, and Cw3 Ag of the parental cell line while retaining expression of HLA-Cw4. We find, however, that CTL specific for HLA-B35 lyse C1R cells, suggesting that expression of HLA-B35 is also retained. To resolve this paradox we examined the expression of HLA-A,B,C genes and proteins in C1R cells. The results are consistent with deletion of the HLA-A3, Bw62, Cw3 haplotype and retention of the HLA-A2, B35, Cw4 haplotype in C1R. Although present, the HLA-A2 gene appears not to be transcribed. As expected, the HLA-Cw4 gene is transcribed and the protein expressed at normal levels. Transcription of the HLA-B35 gene is also normal and comparable to that of HLA-Cw4. However, expression of the HLA-B35 protein is reduced to a few percent of the parental level. Comparison of the nucleotide sequence of B35 alleles from C1R and Hmy2 revealed that reduced translation in C1R is caused by a point mutation (ATG to TTG) in the translation initiation codon. The HLA-B35 allele from C1R and Hmy2 represents a novel subtype, B3503, differing from B3501 by replacement of serine by phenylalanine at the peptide binding position 116. This study shows cell surface levels of a class I molecule which are insensitive to lysis by antibody and complement can be readily recognized by alloreactive T cells, further illustrating the relative sensitivity of Ag recognition by T cells.
HLA - A、B阴性突变细胞系C1R在I类MHC基因的功能研究中被广泛用作转染受体。它是通过三轮诱变和用抗HLA单克隆抗体进行免疫选择，从正常B细胞系Hmy2衍生而来的。血清学鉴定C1R对亲代细胞系的HLA - A2、A3、B35、Bw62和Cw3抗原呈阴性，同时保留HLA - Cw4的表达。然而，我们发现，对HLA - B35特异的CTL可裂解C1R细胞，这表明HLA - B35的表达也被保留。为了解决这一矛盾，我们检测了C1R细胞中HLA - A、B、C基因和蛋白的表达。结果与C1R中HLA - A3、Bw62、Cw3单倍型的缺失以及HLA - A2、B35、Cw4单倍型的保留一致。虽然存在，但HLA - A2基因似乎不转录。正如预期的那样，HLA - Cw4基因转录且蛋白以正常水平表达。HLA - B35基因的转录也正常，与HLA - Cw4相当。然而，HLA - B35蛋白的表达降至亲代水平的百分之几。对C1R和Hmy2的B35等位基因核苷酸序列的比较显示，C1R中翻译减少是由翻译起始密码子中的一个点突变（ATG到TTG）引起的。C1R和Hmy2的HLA - B35等位基因代表一种新的亚型，B3503，在肽结合位置116处苯丙氨酸取代丝氨酸，与B3501不同。这项研究表明，抗体和补体对其裂解不敏感的I类分子的细胞表面水平可被同种异体反应性T细胞轻易识别，进一步说明了T细胞识别抗原的相对敏感性。
