Quantitation of soluble HLA antigens in human serum.

Abstract

For many years we have been interested in soluble HLA antigens and their quantification. Therefore, we follow the literature and are continuously looking for publications concerning this topic. In this context, we have read some papers from the scientific group of Dr. J.C. McDonald which, quite frankly, surprised us. In one of the first papers of Dr. McDonald et al. dealing with soluble HLA antigens (1), the authors stated that “methods to quantitate total sHLA have not appeared.” By studying the articles already published, Dr. McDonald and colleagues should have noted many reports from laboratories measuring soluble HLA class I antigens in human serum or plasma, which appeared several years earlier (2, 3). Even the statement “such studies [they mean quantitation by ELISA] are not yet possible for sHLA-II since there are no secondary antibodies for recognition” is somewhat far from reality, because already in 1991 our group had developed an ELISA system for detection and quantification of soluble HLA class II antigens (4). Moreover, the statement does not even relate to the authors' own reference(5) describing the identification, characterization, and quantitation of soluble HLA antigens in the circulation and peritoneal dialysate of renal patients “... using an enzyme-linked immunoassay...” As a consequence, we informed Dr. McDonald in 1992 that The First International Workshop on Soluble HLA Antigens was to be held in Paris that year, with participation of about 30 laboratories world-wide quantifying soluble HLA molecules, mostly using the ELISA technic(6). The authors completely ignored this summary report, which represented data that already had been published years earlier, because the next paper from this group (7) contained the surprising explanation: “previous assays to quantitate sHLA-I were cumbersome, required radioisotope labeling procedures, or the purification of class I preceding antigen quantitation.” In the most recent paper (8), Dr. McDonald and colleagues make the rather questionable statement in their introduction that:“class I and II HLA antigens are located predominantly on the surface of nucleated cells” and “all individuals... probably have soluble class II HLA antigens in their serum.” The main theme of the paper was the description of different HLA concentrations, depending on the HLA allotype(e.g., HLA-A24,-A29-positive individuals have higher levels compared with others), in serum of healthy individuals and patients after liver transplantation, respectively. Again all of these results have been published some years ago (3, 9-11). By comparing the cited references the reader may form his own opinion. Ulrike Westhoff1 Friedrich Otto Fachklinik Hornheide; Tumor Research; D-48157 Münster, Germany