Biochemical Characterization of Plasma Class I Human Leukocyte Antigens (HLA).

摘要

Biochemical complexity of plasma HLA antigens was investigated to identify and characterize the different molecular weight (M.W.) forms of HLA in plasma and to derive possible mechanisms for generation of plasma HLA. Additionally, plasma HLA was studied in a representative HLA-phenotyped population (n=44, 51% female) to determine plasma HLA patterns and identify factors which influence the expression of different M.W. forms of plasma HLA. Gel filtration chromatography of plasma revealed two distinct pools containing HLA. Pool I had apparent molecular weight of 200,000 D and contained only intact 44 kD HLA that was extractable by Triton X-114 detergent. Pool II had M.W. equivalent to 50,000 D and contained 39 and 36 kD HLA which were not extracted by Triton X-114. NH2-terminal sequence analysis of purified 44 and 39 kD plasma HLA demonstrated identical sequences homologous to the NH2-terminal consensus sequence of cellular HLA. The NH2-terminal sequence for the 36 kD HLA was different from the 44 and 39 kD HLA and also unique, as a search against known protein sequences in the database of Genebank revealed no matches. These results suggest that 1) only the 44 kD plasma HLA possesses the transmembrane domain and 2) the molecular weight of the 39 kD plasma HLA, lacking the hydrophobic transmembrane domain, precludes that it is generated from cleavage of the cytoplasmic tail and transmembrane domain at the carboxyl terminal. (sdw)