Variation in HLA-DM expression influences conversion of MHC class II alpha beta:class II-associated invariant chain peptide complexes to mature peptide-bound class II alpha beta dimers in a normal B cell line.
The maturation of invariant chain (Ii):MHC class II complexes into peptide-loaded alpha beta dimers occurs by proteolytic removal of Ii chain and binding of antigenic peptides derived from exogenous and endogenous Ags. A fragment of the Ii chain (class II-associated invariant chain peptide (CLIP) remains associated with class II alpha beta and is an intermediate in this process. Conversion of alpha beta:CLIP complexes into alpha beta:peptide complexes is facilitated by HLA-DM. Two unique mAbs, specific for I-Ab bound to human CLIP and I-Ab bound to DR alpha peptide, were used to assess the formation of these peptide:class II complexes in a human B lymphoblastoid cell line (B-LCL) (Swei) transfected with I-A(b). In multiple independent Swei:I-Ab transfectants, the amount of human CLIP (hCLIP):I-Ab expressed was inversely proportional to the amount of DR alpha 52-68:I-Ab; quantitative differences in HLA-DM expression accounted for this phenotype. In the low DM transfectant, a substantial proportion of I-Ab, but not DR molecules, was altered structurally and unable to present native protein Ags. Addition of DM transgenes to the DM-low cells resulted in an increase in DR alpha 52-68:I-Ab coupled with a decrease in hCLIP:I-Ab complexes and restoration of exogenous protein Ag presentation. The DR5 molecules in Swei cells, which have a lower affinity for hCLIP than I-Ab, were not affected by low DM expression, suggesting that the amount of DM required for conversion of CLIP:class II to peptide:class II may depend on the affinity of the class II molecules for CLIP or DM.
Ramachandra
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L
Department of Immunology, University of Washington School of Medicine, Seattle 98195, USA.
Kovats
S
S
Eastman
S
S
Rudensky
A Y
AY
D000595:Amino Acid Sequence; D017951:Antigen Presentation; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D002460:Cell Line; D006681:HLA-D Antigens / Q000096:biosynthesis* / Q000502:physiology; D015805:HLA-DR5 Antigen / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000276:immunology; D011487:Protein Conformation; D014162:Transfection
D000944:Antigens, Differentiation, B-Lymphocyte; C416189:H2-M antigens; D006681:HLA-D Antigens; C084245:HLA-DM antigens; D015805:HLA-DR5 Antigen; D000949:Histocompatibility Antigens Class II; C045084:invariant chain