The complexity of HLA-DS molecules. A homozygous cell line expresses multiple HLA-DS alpha chains.

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Abstract
Ia molecules expressed by an HLA-Drw6 homozygous cell line [ELD) were immunoprecipitated with anti-Ia allosera and monoclonal antibodies and analyzed by 2-dimensional gel electrophoresis. The DRw6 homozygous cell line was shown to express 2 DS .beta. chains; this observation extends previous finding that a DR5 homozygous cell line expresses 2 DS .beta. chains and suggests that the expression of at least 2 DS .beta. chain by DR homozygous cell lines is a generalized phenomenon. The data presented here document for the first time that a DR homozygous cell line expresses at least 2 DS .alpha. chains. This cell line expresses at least 2 DS molecules with the potential for the expression of 4 DS molecules. In agreement with previous reports, the cell line was shown to express 2 DR .beta. chains and one DR .alpha. chain that combined to form 2 DR molecules. The molecular specificities of 2 MB1 allosera and 2 MB1-like monoclonal antibodies were also compared in these studies. Both MB1 allosera isolated a single DS molecule, while the MB1-like monoclonal antibodies isolated at least 2 DS molecules. These studies document for the first time that anti-Ia reagents which are specific for the MB1 or MB1-like determinants in population studies do not recognize the same Ia molecules in immunochemical studies. The data presented here for the expression of at least 2 DS .alpha. chains and the location of the MB1 allodeterminant on only one of multiple DS molecules are in agreement with recent studies at the gene level.