SOLUBLE HLA CLASS-I IN THE SERUM OF TRANSPLANT RECIPIENTS

Background Soluble HLA, Class I (S-HLA-I) has been found in serum, pla sma, body fluids, peritoneal dialysates, and urine. S-HLA-I may be a p roduct of membrane shedding, proteolysis, and/or alternate gene splici ng. Previous assays to quantitate S-HLA-I were cumbersome, required ra dioisotope labeling procedures, or the purification of Class I antigen preceding antigen quantitation. The authors developed a solid-phase, enzyme-linked immunoassay that can be used to quantitate S-HLA-I and t o study its relevance in transplantation. Methods A solid-phase enzyme -linked immunoassay employing monoclonal anti-Class I to catch S-HLA-I present in plasma and peroxidase-labeled monoclonal anti-beta2-microg lobulin (B2M) to quantitate bound S-HLA-I was employed. Values were co rrelated with rejection and infection episodes. Pre- and postoperative determinations were made from the sera of liver,9 heart,12 and kidney 20 recipients. Size chromatography was used to compare the molecular w eight of S-HLA-I from baseline and peak serum concentrations obtained during rejection episodes (2 liver, 1 heart, 1 kidney), and from 1 kid ney recipient with a wound infection. Results All 9 liver recipients a nd 12 heart recipients demonstrated a fall in S-HLA-I, or very low ini tial values, for the first 10 days and then a progressive increase in values substantially above preoperative concentrations. Values from re nal recipients were more variable. There were temporary increases in S -HLA-I preceding or during 16 of 20 (80%) biopsy-proven rejections (al l reversible), and in 9 of 11 (83%) episodes of infection (bacterial, viral, and fungal). In heart and liver rejection, as well as the wound infection, the sera contained increased S-HLA-I, which was almost all of the same molecular weight (approximately 52,000 daltons). In serum from the one patient with renal rejection, two additional S-HLA-I pea ks occurred, one with a molecular weight near 1,000,000 daltons and th e second at a molecular weight approximately 11,000 daltons suggesting cellular breakdown of the donor organ. Conclusion In summary, differe nt patterns of S-HLA-I concentrations occur after kidney transplantati on. Most liver and heart recipients reached a steady state higher than preoperative levels. Transient increases in S-HLA-I occurred with rej ection and infection. In one severe rejection episode, larger and smal ler fractions of S-HLA-I were detected and may represent cell membrane breakdown.