The soluble pool of beta 2-microglobulin free HLA class I alpha-chains. Qualitative and quantitative characterization.
Previous studies have demonstrated that HLA class I heterodimers are present in plasma and cell culture supernatants. They can be precipitated by mAb the binding of which is dependent on the proper association of the polymorphic alpha-chain with beta 2-microglobulin (beta 2-m). The molecular mass of the alpha-chain ranges from 45 to 35 kDa with a number of intermediate products. We report on the identification of 35-kDa soluble beta 2-m free HLA class I H chains immunoprecipitated by mAb LA45 from cell culture media of activated B and T cells. Furthermore, a peptide-based competitive immunosorbent assay was established to determine the amounts of soluble HLA class I alpha-chains. By means of this assay, we formally proved the specificity of mAb LA45 for a linear epitope on HLA class I H chains centered on residues arginine-asparagine at positions 62 and 63 of the alpha 1-domain. PHA or rIL-2 were identified as efficient stimuli for PBMC leading to the generation of soluble beta 2-m free HLA class I H chains. Testing of cell lines representing distinct stages of hematopoietic differentiation demonstrated a significant correlation between cell surface expression of beta 2-m free HLA class I H chains and amounts of soluble LA45 reactive molecules. However, three of six human T lymphotropic virus type I transfected cell lines, although expressing beta 2-m free H chains, do not generate soluble molecules. Finally, human sera were found to contain considerable amounts of beta 2-m free HLA class I H chains. The average amount of these molecules in sera of individuals with one positive LA45 allele was determined to be 46.9 +/- 38.6 nM/liter.
Pickl
W F
WF
Institute for Immunology, University of Vienna, Austria.
Majdic
O
O
Faé
I
I
Reuschel
R
R
Holter
W
W
Knapp
W
W
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D011817:Rabbits; D001613:beta 2-Microglobulin / Q000032:analysis*
D000911:Antibodies, Monoclonal; D015395:Histocompatibility Antigens Class I; D007376:Interleukin-2; D001613:beta 2-Microglobulin