beta(2)-mu-free HLA class I heavy chain levels in sera of healthy individuals. Lack of association with beta(2)-mu-associated HLA class I heavy chainlevels and HLA phenotype

We have applied a double-determinant immune assay (DDIA) to measure soluble beta(2)-microglobulin (beta(2)-mu)-free HLA class I heavy chains in serum. The mean concentration of beta(2)-mu-free HLA class I heavy chains in seru m from 120 healthy subjects was 0.21+/-0.24 mu g/ml. The individual serum l evels of beta(2)-mu-free HLA class I heavy chains had a wide distribution, did not seem ia be related with HLA phenotype, were stable over time and di d not change with age. The serum levels of soluble beta(2)-mu-free HLA clas s I heavy chains did not correlate with those of soluble beta(2)-mu-associa ted HLA class I heavy chains, suggesting that their release is independentl y regulated. Three forms of soluble beta(2)-mu-free HLA class I heavy chain s, with apparent molecular masses of 44, 39 and 37-35 kD, respectively, cir culate in human serum, These results provide a useful background to assess the serum level of soluble beta(2)-mu-free HLA class I heavy chains in path ological conditions and to evaluate their putative immunoregulatory functio n.