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Published on: February 28, 2019
Biosynthesis and glycosylation of the invariant chain associated with HLA-DR antigens
The biosynthesis and glycosylation of the invariant (I) chain associated with HLA-DR alpha-beta chain complexes has been examined in human B lymphoblastoid cell lines. Two-dimensional polyacrylamide gel electrophoresis of HLA-DR immune precipitates from extracts of metabolically labeled cells demonstrated a processes form of the I chain, called Ip, which consists of a series of spots beginning near the basic I chain spot and ending near the acidic alpha spots. Pulse/chase labeling yielded information on the kinetics of processing of the invariant chain, as well as the finding that the association of Ip with alpha-beta chain complexes appears to be transient. Neuraminidase treatment of immune precipitates confirmed that Ip was a form of the I chain containing up to eight sialic acid residues. Labeling in the presence of tunicamycin suggested the presence of both N-linked and O-linked oligosaccharide units on the invariant chain. This processing pattern does not appear to be an artifact of B cell lines; it was seen in peripheral blood lymphocytes, freshly purified monocytes, and in an interleukin 2-dependent continuous T cell line that expressed HLA-DR. In addition, there appears to be a free pool of the invariant chain and its processed form that is not found associated with DR alpha and beta chains.
The biosynthesis and glycosylation of the invariant (I) chain associated with HLA-DR alpha-beta chain complexes has been examined in human B lymphoblastoid cell lines. Two-dimensional polyacrylamide gel electrophoresis of HLA-DR immune precipitates from extracts of metabolically labeled cells demonstrated a processes form of the I chain, called Ip, which consists of a series of spots beginning near the basic I chain spot and ending near the acidic alpha spots. Pulse/chase labeling yielded information on the kinetics of processing of the invariant chain, as well as the finding that the association of Ip with alpha-beta chain complexes appears to be transient. Neuraminidase treatment of immune precipitates confirmed that Ip was a form of the I chain containing up to eight sialic acid residues. Labeling in the presence of tunicamycin suggested the presence of both N-linked and O-linked oligosaccharide units on the invariant chain. This processing pattern does not appear to be an artifact of B cell lines; it was seen in peripheral blood lymphocytes, freshly purified monocytes, and in an interleukin 2-dependent continuous T cell line that expressed HLA-DR. In addition, there appears to be a free pool of the invariant chain and its processed form that is not found associated with DR alpha and beta chains.
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