Soluble HLA class I in the serum of transplant recipients

Soluble HLA, Class I (S-HLA-I) has been found in serum, plasma, body fluids, peritoneal dialysates, and urine. S-HLA-I may be a product of membrane shedding, proteolysis, and/or alternate gene splicing. Previous assays to quantitate S-HLA-I were cumbersome, required radioisotope 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 to study its relevance in transplantation.

A solid-phase enzyme-linked immunoassay employing monoclonal anti-Class I to catch S-HLA-I present in plasma and peroxidase-labeled monoclonal anti-beta 2-microglobulin (B2M) to quantitate bound S-HLA-I was employed. Values were correlated with rejection and infection episodes. Pre and postoperative determinations were made from the sera of liver, heart, and kidney recipients. Size chromatography was used to compare the molecular weight of S-HLA-I from baseline and peak serum concentrations obtained during rejection episodes (2 liver, 1 heart, 1 kidney), and from 1 kidney recipient with a wound infection.

All 9 liver recipients and 12 heart recipients demonstrated a fall in S-HLA-I, or very low initial values, for the first 10 days and then a progressive increase in values substantially above preoperative concentrations. Values from renal recipients were more variable. There were temporary increases in S-HLA-I preceding or during 16 of 20 (80%) biopsy-proven rejections (all 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 peaks occurred, one with a molecular weight near 1,000,000 daltons and the second at a molecular weight approximately 11,000 daltons suggesting cellular breakdown of the donor organ.

In summary, different patterns of S-HLA-I concentrations occur after kidney transplantation. Most liver and heart recipients reached a steady state higher than preoperative levels. Transient increases in S-HLA-I occurred with rejection and infection. In one severe rejection episode, larger and smaller fractions of S-HLA-I were detected and may represent cell membrane breakdown.