Rheumatology Advance Access originally published online on November 23, 2006
Rheumatology 2007 46(3):555-556; doi:10.1093/rheumatology/kel390
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On the reactivity of monoclonal antibodies specific for different forms of HLA class I molecules
Institut für Immungenetik, Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Humboldt-Universität zu Berlin, Spandauer Damm 130, 14050 Berlin, Germany.
Correspondence to: B. Uchanska-Ziegler E-mail: barbara.uchanska-ziegler{at}charite.de
SIR, Raine and colleagues [1] seek to assess the relative levels of fully assembled MHC class I molecules and free HLA class I heavy chains (FHC) by employing two well-studied monoclonal antibodies (mAb), W6/32 [2] and HC10 [3, 4]. With regard to W6/32, this reagent recognizes not only ‘HLA-A, -B, -C and -G alleles’ [1] but in addition also detects HLA-E [5] and HLA-F [6] antigens. Raine and co-workers claim also that HC10 recognizes ‘unfolded’ HLA class I heavy chains of ‘HLA-B, -C and -G alleles’ and cite two articles [4, 7] as support. However, neither of these articles shows unambiguously that HC10 recognizes HLA-G. If anything, they demonstrate that HC10 detects only HLA-B and -C molecules reliably, and other authors have come to the same conclusion [8]. Consequently, the statement by Raine and co-workers [1] that HC10 reactivity with cells of the extravillous cytotrophoblast likely reflects ‘the presence of FHC HLA-G structures’ is untenable. HC10 reactivity with these placental cells indicates the expression of HLA-C molecules, because the presence of HLA-B antigens could be excluded with additional mAb directed against these molecules [8]. On the other hand, HCA2 [4], another mAb raised against HLA heavy chains, shows a reactivity spectrum that clearly includes also HLA-G molecules [3, 4, 7–9]. Both mAb detect FHC also by western blotting, indicating that certain HLA class I molecules lacking ß2-microglobulin can be recognized either by HC10 or by HCA2 [3, 4, 7–9]. However, to the best of our knowledge, there is no evidence that these reagents react exclusively with FHC. Since peptide-devoid HLA class I antigens can persist for prolonged periods of time, possibly in a locus- or even an allele-dependent manner, on the cell surface [10], it may well be that a fraction of these molecules reacts with HC10 or HCA2, without being peptide- and ß2-microglobulin-devoid FHC.
Apart from the work by Raine and colleagues [1], there are other publications [11, 12] in which the reactivities of W6/32 and HC10 are compared with each other. While the latter two studies employed cell lines with certain defects affecting the expression of HLA class I antigens, thus permitting an evaluation of the reactivity of these mAb predominantly with transfected HLA-B27 subtypes [11, 12], Raine and co-workers [1] used blood and tissue from healthy and diseased individuals. As these cells invariably express a variety of HLA class I molecules, it is considerably more difficult to relate the reactivities of two mAb with very different, partially overlapping specificity to each other and, in particular, to derive inferences regarding one of these HLA class I alleles, e.g. HLA-B27 [1].
Therefore, when cells from human donors are to be analysed, reliable results can only be obtained when a carefully chosen panel of mAb [8, 13] is employed to assess the extent to which a subpopulation of HLA class I molecules has lost their peptides and might exist as structurally distinct form on the cell surface. Studies such as that by Raine and colleagues [1] that do not meet these minimal requirements, are likely to arrive at premature, possibly even misleading, conclusions.
The authors have declared no conflicts of interest.
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