A human lymphoblastoid B line with an abnormally large MHC class II beta chain

We have examined the MHC class II beta chains in lymphoblastoid cell lines from over 200 individuals and describe one line which possesses, in addition to normal beta chains, a species of beta chain of unusually high Mr and abnormal pI which appears to be a product of the DR locus. This abnormality in Mr, detected by SDS-gel electrophoresis, was apparent only in the presence of mercaptoethanol and was shown to be due to difference in polypeptide chain length rather than to extra glycosylation.