Tibensky D, DeMars R, Holowachuk E W, Delovitch T L
Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada.
J Immunol. 1989 Jul 1;143(1):348-55.
Our previous studies suggested that a serologically undetectable HLA-C blank allele (HLA-CwBL18) is either a variant Cw5 allele or a novel HLA-C Ag. To examine these possibilities, the CwBL18 and Cw5 genes from the TCC (HLA-A1, -A2, -B52, -B18, -Cw-, -Cw-) and QBL (HLA-A26, -B18, -Cw5) EBV-transformed B lymphoblastoid cell lines (LCL) were cloned, sequenced, and transferred into HLA-A, -B, -C null LCL mutant .221 cells. The CwBL18 Ag was detected on the cell surface of CwBL18 transferents by flow cytometry with the anti-class I mAb W6/32 but not by complement-mediated cytotoxicity with currently available HLA-C specific antisera. Sequence analysis of the Cw-BL18 gene indicated that the CwBL18 Ag is "C"-like because it contains all C-locus-specific residues and amino acid replacements commonly found in HLA-C alleles. However, the amino acid sequence of the CwBL18 Ag is unusual; CwBL18 lacks unique allele-specific residues when compared with the sequences of other HLA-C alleles. Moreover, apart from the C-locus-specific differences, the sequence of CwBL18 is identical to the HLA class I consensus sequence. This striking homology of CwBL18 to other HLA class I alleles suggests that CwBL18 may be a weak Ag. Taken together, these data demonstrate that CwBL18 is not a variant Cw5 Ag but is a newly described HLA-C Ag. In contrast to CwBL18, the Cw5 Ag is serologically detectable on the cell surface of Cw5 transferents with HLA-specific allo-antisera. Rather unexpectedly, Cw5 was usually expressed at a lower level than CwBL18 on the surface of .221 transferents as evaluated by W6/32 mAb binding analyses. The sequence of Cw5 revealed several unique amino acid replacements. Two of these substitutions, at residue 35 of the alpha 1 domain and residue 275 of the transmembrane domain, may be responsible for the reduced cell surface expression of Cw5. Additional unique replacements at residues 138 and 177 of the alpha 2 domain suggest that these amino acids may be important in the formation of an epitope recognized by a Cw5-specific antibody.
我们之前的研究表明，血清学检测不到的HLA - C空白等位基因（HLA - CwBL18）要么是Cw5等位基因的变体，要么是一种新型的HLA - C抗原。为了探究这些可能性，从TCC（HLA - A1、- A2、- B52、- B18、- Cw -、- Cw -）和QBL（HLA - A26、- B18、- Cw5）EB病毒转化的B淋巴母细胞系（LCL）中克隆、测序了CwBL18和Cw5基因，并将其转入HLA - A、- B、- C缺失的LCL突变体.221细胞中。通过流式细胞术使用抗I类单克隆抗体W6/32在CwBL18转染细胞的细胞表面检测到了CwBL18抗原，但使用目前可用的HLA - C特异性抗血清通过补体介导的细胞毒性检测未检测到。对Cw - BL18基因的序列分析表明，CwBL18抗原具有“C”样特征，因为它包含所有C位点特异性残基以及HLA - C等位基因中常见的氨基酸替换。然而，CwBL18抗原的氨基酸序列并不寻常；与其他HLA - C等位基因的序列相比，CwBL18缺乏独特的等位基因特异性残基。此外，除了C位点特异性差异外，CwBL18的序列与HLA I类共有序列相同。CwBL18与其他HLA I类等位基因的这种显著同源性表明CwBL18可能是一种弱抗原。综上所述，这些数据表明CwBL18不是Cw5抗原的变体，而是一种新描述的HLA - C抗原。与CwBL18不同，使用HLA特异性同种异体抗血清在Cw5转染细胞的细胞表面可血清学检测到Cw5抗原。相当出乎意料的是，通过W6/32单克隆抗体结合分析评估，在.221转染细胞表面，CwBL18的表达水平通常低于Cw5。Cw5的序列揭示了几个独特的氨基酸替换。其中两个替换，一个在α1结构域的第35位残基，另一个在跨膜结构域的第275位残基，可能是导致Cw5细胞表面表达降低的原因。α2结构域第138位和第177位残基的其他独特替换表明，这些氨基酸可能在由Cw5特异性抗体识别的表位形成中起重要作用。
